Every portable generator gets a score from 0 to 100% built from seven factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Generators are ranked within their size, by rated running watts on gasoline: small (under 5,000 W), mid-size (5,000 to 8,999 W) and large (9,000 W and up).
This list covers open-frame (conventional) generators. Inverter generators are quieter and make cleaner power, cost more per watt, and are ranked on their own scale.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per running watt | 30% |
| Run time | hours on a tank at 50% load | 15% |
| Fuel options | gasoline, propane and natural gas | 15% |
| Home hookup | 240 V outlet for a transfer switch | 15% |
| CO safety | carbon monoxide shutoff | 10% |
| Warranty | warranty length | 10% |
| Starting | electric or remote start | 5% |
Where the numbers come from
Running and starting watts, run time, fuel options, outlets, safety features and warranty come from the maker’s spec page, manual or warranty terms, linked on every product page. Independent measurements, where a reviewer has published them, are shown in their own table.
Reference points by size
| Size | Price per running watt, scoring 0 → 100 | Run time at 50% load, 0 → 100 |
|---|---|---|
| Small (under 5,000 W) | $0.35 → $0.10 | 4 → 14 hours |
| Mid-size (5,000 to 8,999 W) | $0.30 → $0.09 | 4 → 14 hours |
| Large (9,000 W and up) | $0.25 → $0.08 | 4 → 14 hours |
The factors
Value is the lowest checked price divided by the rated running watts on gasoline. Prices are checked and dated on every page. Small generators always cost more per watt, so each size has its own scale. A generator with no current price gets the neutral middle score.
Run time is the maker’s rated hours on a full tank of gasoline at 50% load, the load most makers of open-frame generators quote. Where the maker rates run time at another load, it’s scaled to 50% assuming fuel use rises in step with load above idle, and the product page says so.
Fuel options scores gasoline only as zero, gasoline or propane (dual fuel) as 70%, and gasoline, propane or natural gas (tri-fuel) as full marks. Propane keeps for years without going stale and is easier to find after a storm; natural gas can run from a house’s gas line for as long as the outage lasts.
Home hookup is full marks for a 240 V outlet (L14-30, L14-50 or 14-50R) that feeds both legs of a house’s panel through a transfer switch or inlet box, so 240 V loads like a well pump work. An L5-30 alone, which reaches only one leg at 120 V, scores 40%; household outlets only, zero.
CO safety is full marks for a carbon monoxide sensor that shuts the engine off (sold as CO-Sense, COsense, CO Shield, CO Mind or similar), and zero without one. It doesn’t make indoor use safe, but it’s the best protection against a generator running too close to a house.
Warranty is the length of the maker’s residential warranty, from 1 year (zero) to 4 years (full marks), with the common 3 years at two-thirds.
Starting scores a pull cord as zero, push-button or key electric start as 80% and a remote fob or app start as full marks.
What isn’t scored
Noise, weight, propane output, a 120 V full-power switch and CARB compliance are shown and can be sorted or filtered, but aren’t scored. Few makers publish a noise figure for open-frame generators, and those that do measure at different loads, so the figures can’t be compared fairly. The dual fuel list shows generators that run on propane, the tri fuel list those that also run on natural gas, and the transfer switch ready list those with a 240 V outlet.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each size. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.