How long will a generator run on a 20 lb propane tank?
Champion’s 3500 W dual-fuel generator (3,150 running watts on propane) is rated 10.5 hours at half load on a 20 lb tank — about 1.9 lb of propane an hour, or 0.45 gallons.
How to work it out
- Spec: 3,150 W × 50% × 10.5 h = 16.54 kWh from 4.73 gal × 91,452 Btu/gal → 13% efficient
- Your load: 1,575 W × 3,412 Btu/kWh ÷ 13% = 41,181 Btu an hour = 0.45 gal of propane an hour
- 4.73 gal ÷ 0.45 gal/h = 10.5 hours
The 20 lb cylinder — the barbecue grill size — is what dual-fuel generator spec sheets quote. It holds 20 lb of propane, about 4.7 gallons at NIST’s 4.23 lb per gallon, which is noticeably less energy than 5 gallons of gasoline.
Adjust for your project
More options: Spec load · Spec hours 2
- In hours and minutes
- 10 h 30 min
- Propane per hour
- 1.9 lb
- Propane per 24 hours
- 45.7 lb
- Generator efficiency (fuel to electricity)
- 13%
- Fuel energy burned per hour
- 41,181 Btu
Runtime at other loads
| Your load | Runtime at your load | Propane per hour |
|---|---|---|
| 500 | 33.1 hours | 0.6 lb |
| 1000 | 16.5 hours | 1.21 lb |
| 1750 | 9.5 hours | 2.12 lb |
| 2500 | 6.6 hours | 3.02 lb |
| 3500 | 4.7 hours | 4.23 lb |
What to know about running a generator on propane
- Bigger tanks scale it up. A 30 lb cylinder gives about 15.75 hours at the same load; a 100 lb cylinder about 52.5 hours. The arithmetic is the same — pounds ÷ pounds per hour.
- Bigger generators drink faster. Champion’s 6500 W dual-fuel model is rated 6.5 hours at half load on a 20 lb tank, about 3.1 lb an hour.
- Cold weather can starve it. Propane leaves the tank as vapor, and a small cylinder in freezing weather may not vaporize fast enough for a big load. Larger tanks help.
- Fewer watts on propane. Dual-fuel generators are rated lower on propane — 3,150 vs 3,500 running watts for this model — largely because a cylinder-full of propane–air mixture carries less energy into the engine than the same volume of gasoline–air mixture.
How long the same tank lasts on a heater or grill is on how long a 20 lb propane tank lasts for heating, and a 100 lb tank on how long a 100 lb propane tank lasts. The gasoline version is how long a generator runs on 5 gallons of gas.
Different size? Use the full Generator Fuel & Runtime Calculator.
What you’ll need
- Dual-fuel portable generatorPremium price
Runs on gasoline or propane. Propane stores for years without going stale; expect somewhat fewer watts on propane.
See options on Amazon (opens in a new tab) - Propane tank gaugeBudget price
Shows roughly how much is left so you are not guessing halfway through a cold night or a long outage.
See options on Amazon (opens in a new tab) - Battery-operated carbon monoxide alarmBudget price
CPSC advises battery or battery-backup CO alarms whenever a generator is in use. Look for UL 2034 certification and test monthly.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How long will a 30 lb propane tank run a generator at half load?
About 15.8 hours for the same 3500 W dual-fuel generator.
How long will a 100 lb propane tank run a generator?
About 52.5 hours (52 h 30 min) at half load.
How much propane does a generator use in 24 hours?
About 45.7 lb at half load — more than two 20 lb tanks.
Other common sizes
- How long a generator runs on 5 gallons of gas — About 14.9 hours (3500 W generator at half load)
Sources
- U.S. Energy Information Administration — British thermal units (Btu) (opens in a new tab) — Heat content: gasoline 120,214 Btu/gal, diesel 137,381 Btu/gal, propane 91,452 Btu/gal; 1 kWh = 3,412 Btu.
- NIST Chemistry WebBook — Thermophysical properties of propane (saturated liquid) (opens in a new tab) — Liquid propane is about 31.6 lb/ft³ at 60 °F, which is 4.23 lb per US gallon (4.09 at 80 °F).
- Champion Power Equipment — 3500-Watt Dual Fuel Generator (model 201213) specifications (opens in a new tab) — 3,500 running / 4,000 starting watts on gasoline; 14 h at 50% load on 4.7 gal; 10.5 h at 50% load on a 20 lb propane tank; 120 V 30 A TT-30R RV outlet.
- Champion Power Equipment — 6500-Watt Dual Fuel Generator (model 201077) specifications (opens in a new tab) — 6,500 running / 8,125 starting watts on gasoline (5,850 / 7,325 on propane); 11 h at 50% load on 7.7 gal; 6.5 h at 50% load on a 20 lb propane tank.
- Champion Power Equipment — 2000-Watt Dual Fuel Inverter (model 201230) specifications (opens in a new tab) — 1,700 running / 2,000 starting watts on gasoline (1,530 / 2,000 on propane); 11.5 h at 25% load on 1.05 gal; 34 h at 25% load on a 20 lb propane tank.
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.