Portable generator ratings are the numbers on the box: watts, decibels, run time, harmonic distortion and safety certifications. They look like plain facts. In practice, each one is measured in a way that the maker chooses, and two generators with the same headline number can perform very differently.
A “4,500-watt” generator from one brand can make the same real power as a “3,500-watt” generator from another. A run time of “14 hours” may be measured at a quarter of full load. A noise figure of “53 dB” may apply only when the engine is idling.
None of this is dishonest. It is simply how the industry works. Once you know the rules, you can compare any two generators fairly in about a minute. This guide explains every rating you will meet, shows how real models use them, and ends with a simple method for reading a spec sheet. We have not tested these generators. Every figure comes from the makers’ own published specifications.
Portable generator ratings at a glance
Compare like with like, and read the small print beside each number
Example figures come from makers’ product pages and listings, checked October 2026.
Quick answer
Size a generator on its running watts, also called rated watts. Starting or peak watts last only a moment. Check what load a run time is quoted at: open-frame generators usually use 50% load and inverters often use 25%. Noise is given in dBA, usually measured 23 feet away, and often at a light load. THD under 3% means clean power for electronics. For safety, look for a carbon monoxide shutoff that meets ANSI/PGMA G300 or UL 2201. Treat customer star ratings as a clue, not a measurement.
How we put this guide together
We have not tested these generators, and we do not publish star ratings or scores of our own. Example specifications come from the product pages, manuals and listings of Honda, Champion, Generac, Westinghouse, WEN and DuroMax, checked in October 2026. Carbon monoxide standards are described from the published standards and from US Consumer Product Safety Commission documents. The national park noise limit is from 36 CFR 2.12. Where a maker does not publish a rating, we say so.
In this guide
- Rating 1: Watts
- Rating 2: Run Time
- Rating 3: Noise
- Rating 4: THD, or How Clean the Power Is
- Rating 5: Carbon Monoxide Safety
- Rating 6: Emissions Labels
- Rating 7: Engine, Weight and Warranty
- What About Star Ratings and Reviews?
- How to Read a Spec Sheet in One Minute
- Tools and Examples
- Common Mistakes When Reading Generator Ratings (and the Fix)
- Pro Tips for Comparing Generators
- Real-Life Scenarios: Reading the Ratings
- Portable Generator Ratings: FAQ
- Your Generator Ratings Checklist
Rating 1: Watts
Watts measure power. A generator has two wattage ratings, and mixing them up is the most common mistake buyers make.
Running watts
Running watts is the power a generator can supply continuously. Makers also call it rated watts or continuous watts. This is the number to compare, and the number to size on.
Starting watts
Starting watts is a short burst, lasting a few seconds, for starting electric motors. Makers also call it peak, surge or maximum watts. It is always the larger of the two numbers, which is why it so often ends up in the product name.
How brands put watts in the name
Here is where it gets confusing. Brands do not agree on which number goes in the name.
| Generator | Number in the name | Running watts | Starting watts |
|---|---|---|---|
| Honda EU2200i | 2,200, the maximum | 1,800 | 2,200 |
| Champion 3500W open-frame generator | 3,500, the running figure | 3,500 | 4,375 |
| Champion 4500-Watt inverter | 4,500, the starting figure | 3,500 | 4,500 |
| Generac “10,000 Starting Watt” GP8000E | 10,000 starting, 8,000 in the model code | 8,000 | 10,000 |
| Westinghouse “12500 Peak Watt” WGen9500DFc | 12,500 peak, 9,500 in the model code | 9,500 | 12,500 |
| DuroMax XP13000HX | 13,000, the starting figure | 10,500 | 13,000 |
Look at the two Champion rows. A “3500W” generator and a “4500-Watt” generator from the same company make exactly the same running power. Champion names open-frame models by running watts and inverter models by starting watts.
Key insight: ignore the number in the name. Find the line in the specifications that says running or rated watts, and compare that.
Watts change with fuel
Dual fuel and tri fuel generators have a separate rating for each fuel. Gasoline always gives the most.
| Generator | On gasoline | On propane | On natural gas |
|---|---|---|---|
| Champion 11,000-Watt tri fuel inverter | 9,000 | 8,100 | 7,290 |
| Generac GP9500E Tri Fuel | 9,500 | 8,550 | 7,000 |
| Westinghouse 12500 Peak Watt tri fuel | 9,500 | 8,500 | 7,500 |
The pattern is consistent: about 10% less on propane, and 20% or more less on natural gas. If you plan to run on propane, size against the propane figure.
Watts change with altitude
Engines make less power in thin air. Champion’s manual for one of its portables gives a figure of about 3.5% less output for every 1,000 feet above sea level. At 5,000 feet, a 3,500-watt generator delivers roughly 2,900 watts. Ratings on the box are for sea level.
Watts are limited by the outlet
A generator can only deliver what its outlets can pass. Multiply amps by volts to find the limit.
| Outlet | Rating | Maximum power | Typical use |
|---|---|---|---|
| 5-20R duplex | 20 amps at 120 volts | 2,400 watts | Household plugs |
| TT-30R | 30 amps at 120 volts | 3,600 watts | 30-amp RVs |
| L5-30R | 30 amps at 120 volts, locking | 3,600 watts | Generator cords |
| L14-30R | 30 amps at 120/240 volts, locking | 7,200 watts | 30-amp transfer switches |
| 14-50R | 50 amps at 120/240 volts | 12,000 watts | 50-amp transfer switches and RVs |
This matters on mid-size generators. An 8,000-watt generator whose largest outlet is an L14-30R can only send 7,200 watts through that outlet to your transfer switch.
Our Generator Size Calculator helps you find the running and starting watts you need.
Rating 2: Run Time
Run time tells you how long a tank of fuel lasts. It is the rating most affected by small print.
Always ask: at what load?
A generator burns fuel in proportion to the work it does. Run time is therefore quoted at a stated load, and makers choose different ones.
Champion’s product pages show the pattern clearly. Its open-frame generators quote run time at 50% load. Its enclosed inverters quote run time at 25% load. An inverter slows its engine at light load, so the 25% figure looks very good.
| Generator | Tank | Run time claim | Load behind the claim |
|---|---|---|---|
| Champion 3500W open frame | 4.7 gallons | 12 hours | 50% load |
| Champion 2500-Watt Ultralight inverter | 1.1 gallons | 11.5 hours | 25% load |
| Generac GP2500i inverter | About 1 gallon | 8 hours, or 5.5 hours | 25% load, or 50% load |
| Generac iQ3800 Dual Fuel inverter | 3.28 gallons | Up to 20 hours | 25% load |
The Generac GP2500i row shows what a difference the load makes. The same generator runs for 8 hours at a quarter load and 5.5 hours at half load, according to its listing.
Turn run time into fuel use
A more honest way to compare is gallons per hour. Divide the tank size by the run time.
The Champion 3500W open-frame generator uses 4.7 gallons in 12 hours at half load. That is about 0.39 gallons an hour while delivering 1,750 watts. Over a three-day outage, running around the clock at that load, it would use about 28 gallons. That number matters more than “12 hours” when you are planning fuel storage.
Our guide to how much gas a generator uses has more worked examples.
Rating 3: Noise
Noise is rated in decibels, written dB or dBA. The A means the measurement is weighted to match human hearing.
Three things to check on any noise rating
Distance. Sound fades with distance. Most makers measure at 23 feet, which is 7 meters. Champion’s pages state this. A figure taken at a different distance cannot be compared directly.
Load. An inverter is much quieter at light load, because the engine slows down. Honda rates the EU2200i at 48 to 57 dB(A), a range from light load to rated load. Generac’s listing for the GP2500i gives 53 dB(A) at 25% load. A single low number, with no load stated, is usually the light-load figure.
The scale. Decibels are not like inches. Every increase of 10 dB sounds roughly twice as loud. So a 68 dBA generator does not sound 30% louder than a 52 dBA one. It sounds about three times as loud.
| Generator | Type | Published noise rating | Condition stated |
|---|---|---|---|
| Honda EU2200i | Inverter | 48 to 57 dB(A) | Light load to rated load |
| Westinghouse iGen2550c | Inverter | As quiet as 52 dBA | Not stated in the listing |
| Champion 2500-Watt Ultralight | Inverter | 53 dBA | At 23 feet |
| Generac GP2500i | Inverter | 53 dB(A) | At 25% load |
| Champion 4500-Watt dual fuel inverter | Inverter | 61 dBA | At 23 feet |
| Champion 3500W | Open frame | 68 dBA | At 23 feet |
| Champion 9,200-watt class | Open frame | 74 dBA | At 23 feet |
Champion describes 68 dBA as about as loud as a vacuum cleaner. Normal conversation is around 60 dBA.
A legal noise limit worth knowing
In US national parks, federal regulation 36 CFR 2.12 prohibits running a generator in a way that exceeds 60 decibels on the A-weighted scale at 50 feet. Most small inverters meet that. Most open-frame generators do not. Many campgrounds also set quiet hours.
Rating 4: THD, or How Clean the Power Is
THD stands for total harmonic distortion. It measures how far the generator’s electricity strays from the smooth wave that utility power has. Lower is better.
- Inverter generators build their output electronically. Generac, Westinghouse and others list their inverters at under 3% THD. That is clean enough for computers, televisions and modern appliance control boards.
- Conventional generators make power directly from the alternator. Their distortion is higher and varies with load. Some makers publish it. Generac lists its XD5000E diesel at 6% THD. Many open-frame generators have no published figure at all.
If a maker does not publish THD for an open-frame generator, assume it is not as clean as an inverter. Motors, heaters and lights do not mind. For sensitive electronics, use an inverter generator, or put a quality surge protector or a battery backup unit between the generator and the device.
Our guide to inverter vs conventional generators explains the two designs.
Rating 5: Carbon Monoxide Safety
This is the rating that can save a life. Portable generators produce carbon monoxide, a gas you cannot see or smell. The US Consumer Product Safety Commission has reported that, on average, about 100 people a year die in the United States from carbon monoxide from portable generators.
Modern generators carry a sensor that shuts the engine off when carbon monoxide builds up. Every brand has its own name for it: CO Shield at Champion, COsense at Generac, CO-MINDER at Honda, CO Alert at DuroMax.
Behind the brand names are two voluntary safety standards.
| Standard | What it requires | What it does not require |
|---|---|---|
| ANSI/PGMA G300-2018 | A sensor that shuts the engine off before carbon monoxide near the generator exceeds set levels, and a warning light that stays on for at least five minutes after a shutoff | It sets no limit on how much carbon monoxide the engine produces |
| UL 2201 | A shutoff system, plus a reduced carbon monoxide emission rate from the engine | It does not require the warning light |
A CPSC staff report in 2022 compared the two using computer simulations of real fatal incidents. It found that generators meeting UL 2201 would prevent nearly all of the simulated deaths, and those meeting G300 about 87%. In April 2023 the commission voted to propose a mandatory federal rule. As far as we could confirm, that rule had not been made final.
How to use this rating
- Buy a generator with a CO shutoff. Check the listing or the manual for the standard it meets. Champion, for example, states that one of its current models meets ANSI/PGMA G300-2018.
- Do not treat it as permission. A shutoff is a backup. It does not make it safe to run a generator in a garage, a porch or a carport.
The rule no rating changes
Run a portable generator outdoors only, at least 20 feet from the house, with the exhaust pointing away from doors, windows and vents. Never run one in a garage, basement, shed, porch or carport, even with the door open. Fit battery-powered carbon monoxide alarms on every level of your home. If an alarm sounds or anyone feels dizzy or sick, get everyone into fresh air and call for help.
Rating 6: Emissions Labels
Two labels describe exhaust emissions. They are separate from carbon monoxide safety.
- EPA certified means the engine meets US federal emissions rules. Every new generator sold in the United States should be.
- CARB compliant means it also meets California’s stricter rules. Makers often call this a 50-state model. A 49-state model cannot be sold in California.
Generac’s site lists several models in both versions. If you live in California, check the listing before you order.
Rating 7: Engine, Weight and Warranty
These supporting numbers help you judge the headline ones.
- Engine displacement, in cc. A bigger engine for the same wattage usually means less strain. Compare models of similar output.
- Weight. A 100-pound generator has wheels for a reason. Check whether the weight is listed dry or with fluids.
- Oil capacity. Small engines hold very little oil. Champion’s 3500-watt model holds 0.6 quart. That is why daily oil checks matter.
- Warranty. Look for two periods. Champion lists 3 years for home use and 270 days for commercial use. Generac’s listings state 3 years residential and 2 years commercial.
- Outlets. GFCI protection matters on job sites. A 30-amp or 50-amp 240-volt outlet matters for a transfer switch.
What About Star Ratings and Reviews?
When people search for generator ratings, they often mean customer star ratings. Those are worth reading, with care.
We do not publish star ratings on this site. They change daily, and a score without context can mislead. Here is how to read them yourself.
- Look at the number of reviews, not just the average. A 4.8 from twelve buyers tells you less than a 4.4 from three thousand.
- Check that the reviews are for your version. Many listings combine several models. A review may describe a different size or fuel type.
- Read the one-star and two-star reviews first. Look for the same fault appearing again and again.
- Separate shipping problems from product problems. A dented frame on arrival is not an engine fault.
- Look at the dates. Recent reviews reflect the current version.
- Notice what reviewers were doing. A generator that failed after sitting for a year with fuel in it failed for a known reason.
- Weigh professional testing where it exists. Independent labs measure noise and power under the same conditions for every model.
Tip: star ratings measure the first month
Most reviews are written in the first weeks of ownership. They tell you about packaging, assembly and first start. They tell you little about year five. For long-term judgment, look at the warranty terms, the parts supply and how the maker’s support line is described.
How to Read a Spec Sheet in One Minute
Here is the method, in order.
- Find the running watts. Ignore the product name.
- Find the starting watts, and check them against your largest motor.
- Check the fuel. If it is dual fuel, read the rating for the fuel you will use.
- Find the run time and the load it was measured at. Convert to gallons per hour if you are comparing models.
- Find the noise figure, the distance and the load.
- Look for THD. Under 3% for electronics.
- Look for the CO shutoff and the standard it meets.
- Check the outlets against how you plan to connect it.
- Check weight, warranty and whether it is a 49-state or 50-state model.
A worked comparison
Here are five small inverter generators, set side by side using each maker’s own published figures.
| Generator | Running watts | Starting watts | Weight | Noise rating |
|---|---|---|---|---|
| Honda EU2200i | 1,800 | 2,200 | 47.4 lb dry | 48 to 57 dB(A) |
| Champion 2500-Watt Ultralight | 1,850 | 2,500 | 39.7 lb | 53 dBA |
| Generac GP2500i | 2,200 | 2,500 | 46.6 lb | 53 dB(A) at 25% load |
| Westinghouse iGen2550c | 1,900 | 2,550 | 40 lb | As quiet as 52 dBA |
| WEN 56235i | 1,900 | 2,350 | 39 lb | Described as conversation level |
Three lessons come out of this table. The names suggest sizes from 2,200 to 2,550, but running watts only range from 1,800 to 2,200. The noise figures are stated in three different ways, so they cannot be ranked precisely. And the lightest models are 8 pounds lighter than the heaviest. That is the kind of difference you feel every time you lift one.
Tools and Examples
We have not tested these products. Details come from the makers’ pages and Amazon listings.
Measure your own loads
P3 P4400 Kill A Watt Electricity Usage Monitor
A plug-in meter that shows the real watts a 120-volt appliance draws. It turns a generator’s ratings into something you can check against your own home.
- DisplaysVolts, amps, watts, kilowatt-hours
- Accuracy on listingWithin 0.2 to 2.0%
- For115-volt AC appliances
- Capacity15 amps
- DisplayLCD
- Warranty1 year limited
- Why it works: a generator’s ratings only matter in relation to your loads. This measures them.
- Who it is best for: anyone choosing a generator size.
- What it solves: guessing from wattage charts that may not match your appliances.
- Keep in mind: it reads steady running watts well. It is not designed to capture the split-second starting surge of a motor. It works on 120-volt plug-in devices only.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
The benchmark inverter
Honda EU2200i 2,200-Watt Portable Inverter Generator
The small inverter that others are measured against. Honda states its noise as a range, from light load to rated load, which is the honest way to give the figure.
- Maximum output2,200 W
- Running output1,800 W
- Sound level48 to 57 dB(A)
- Run time3.2 to 8.1 hours
- Dry weight47.4 lb
- Warranty on listing3-year residential
- Why it works: Honda publishes a range for noise and for run time, so you know the best and the worst case.
- Who it is best for: campers, tailgaters and homes that need a refrigerator, lights and electronics.
- What it solves: noise. Honda says it is quieter than normal conversation.
- Keep in mind: its running output is 1,800 watts, not the 2,200 in its name. The listing says this version is not available in California. Stock was limited when we checked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Honda’s product page and the Amazon listing, checked October 2026.
Light and RV ready
Westinghouse iGen2550c Portable Inverter Generator (2,550 Peak Watts)
A 40-pound inverter with a 30-amp RV outlet. The listing gives 1,900 running watts, THD of 3% or less and a carbon monoxide sensor.
- Running / peak watts1,900 / 2,550
- Weight40 lb
- NoiseAs quiet as 52 dBA
- Run timeUp to 11 hours at 25% load
- Power qualityTHD 3% or less
- OutletsTT-30R, 5-20R duplex, two USB
- Why it works: it states the load behind its run time claim, and it lists THD, which many small generators do not.
- Who it is best for: RV owners and campers who want a 30-amp plug without an adapter.
- What it solves: clean, quiet power in a package one person can carry.
- Keep in mind: the noise figure has no stated load or distance. Expect it to be louder when working hard.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Home backup example
Westinghouse WGen9500DFc Dual Fuel Portable Generator with CO Sensor (12,500 Peak Watts)
A large dual fuel generator that shows several ratings at once: peak watts in the name, running watts in the model code, and a separate rating for each fuel.
- Running watts9,500 gasoline, 8,500 propane
- Peak watts12,500 gasoline, 11,200 propane
- Engine457 cc OHV
- Fuel tank6.6 gallons
- Run timeUp to 12 hours
- Warranty on listing3-year limited
- Why it works: it has remote start, a carbon monoxide shutdown and both 30-amp and 50-amp outlets.
- Who it is best for: homeowners powering essentials through a transfer switch.
- What it solves: long outages, with propane as a second fuel.
- Keep in mind: the “12500” in the name is peak watts. Size on 9,500, or 8,500 if you will use propane. It weighs about 212 pounds and is not quiet.
As an Amazon Associate we earn from qualifying purchases. Specs come from the Amazon listing, checked October 2026.
For model-by-model comparisons, see our portable generator reviews and our guide to the best portable generators.
Common Mistakes When Reading Generator Ratings (and the Fix)
Pro Tips for Comparing Generators
- Make your own table. Write running watts, run time with load, noise with conditions, weight and warranty side by side.
- Download the manual before you buy. It has the real specifications, the oil capacity and the maintenance schedule.
- Prefer ranges to single figures. A maker that publishes a noise range is telling you more.
- Check the model number, not the name, when you compare prices between stores.
- Allow a margin. Plan to use about 80% of the running watts at most.
- Remember altitude. Take off about 3.5% for each 1,000 feet.
- Ask what is missing. No THD figure, no noise conditions or no CO standard is a sign to look further.
Real-Life Scenarios: Reading the Ratings
These are typical situations. They are examples, not reports from real customers.
🏕️ The campground rule
The park says generators must not exceed 60 dBA at 50 feet.
A small inverter rated in the low 50s at 23 feet meets it comfortably. A 74 dBA open-frame generator does not.
Rating that decides: noise
🧊 The refrigerator and the freezer
You want to keep both running through a two-day outage.
Running watts are modest. Starting watts and gallons per hour matter more, because the compressors cycle for days.
Rating that decides: starting watts and fuel use
💻 The home office
You need to power a computer, a monitor and a router.
Any small generator has the watts. Clean power is the issue, so choose an inverter with THD under 3%.
Rating that decides: THD
Portable Generator Ratings: FAQ
What do the watt ratings on a generator mean?
A generator has two. Running watts, also called rated watts, is the power it can supply continuously. Starting watts, also called peak or surge watts, is a brief burst for starting motors. Size your generator on running watts.
What is a good decibel rating for a portable generator?
Small inverter generators are typically rated in the low to mid 50s in dBA at 23 feet under light load, which is quieter than conversation. Open-frame generators are commonly rated at 68 to 76 dBA. Every 10 dB sounds about twice as loud.
What does THD mean on a generator?
THD is total harmonic distortion. It measures how clean the electricity is. Inverter generators are usually rated under 3%, which suits electronics. Conventional open-frame generators have higher distortion, and many makers do not publish a figure.
Why do generator run times differ so much?
Because they are measured at different loads. Open-frame generators usually quote run time at 50% load, and inverters often quote it at 25% load. Always check the load, and compare gallons per hour if you can.
What is ANSI/PGMA G300?
It is a voluntary US safety standard for portable generators. It requires a sensor that shuts the engine off when carbon monoxide builds up around the generator. UL 2201 is a second standard that also requires lower carbon monoxide emissions from the engine.
Are customer star ratings reliable for generators?
They are a useful clue, with limits. Most are written in the first weeks of ownership, and listings often mix several models. Read the low-star reviews, check they match your exact model, and look for repeated faults.
Your Generator Ratings Checklist
- Running watts found and compared.
- Starting watts checked against your largest motor.
- Rating read for the fuel you will use.
- Run time checked for the load it was measured at.
- Noise checked for distance and load.
- THD under 3% if you will power electronics.
- CO shutoff present, and the standard noted.
- Outlets match how you will connect it.
- 49-state or 50-state version confirmed.
- Weight and warranty compared.
- Low-star reviews read for your exact model.
The bottom line
Every generator rating is true under the conditions the maker chose. Your job is to find those conditions. Compare running watts, check the load behind the run time and the noise, and insist on a carbon monoxide shutoff.
As an Amazon Associate we earn from qualifying purchases.
Sources: Product pages, manuals and listings from Honda, Champion, Generac, Westinghouse, WEN and DuroMax for the example specifications; ANSI/PGMA G300-2018 and UL 2201 as published; US Consumer Product Safety Commission staff report (2022), proposed rule (2023) and carbon monoxide information; 36 CFR 2.12 for the National Park Service noise limit; Amazon listings for the products named in this guide. All checked October 2026.
