How long does a 100 lb propane tank last?
A full 100 lb tank holds about 23.64 gal — 2,161,986 Btu. At 30,000 Btu per hour that is about 72.1 hours (3 days) of continuous use.
How to work it out
- 100 lb ÷ 4.23 lb per gallon = 23.64 gal × 91,452 Btu = 2,161,986 Btu
- 2,161,986 Btu ÷ (30,000 Btu/h) = 72.1 hours
The 100 lb cylinder is the tall tank you see beside cabins, food trucks and standby heaters. It holds five times a grill cylinder, and is usually swapped or refilled by a propane dealer.
Adjust for your project
More options: Full · Duty
- In hours and minutes
- 3 days (72 h)
- In days (round the clock)
- 3 days
- Propane in gallons
- 23.64 gal
- Energy in the tank
- 2,161,986 Btu
- Propane used per hour
- 1.39 lb
The same appliance on other tank sizes
| Tank | Runtime | Propane in gallons | Energy in the tank |
|---|---|---|---|
| 1 lb | 0.7 hours | 0.24 gal | 21,620 Btu |
| 20 lb | 14.4 hours | 4.73 gal | 432,397 Btu |
| 30 lb | 21.6 hours | 7.09 gal | 648,596 Btu |
| 40 lb | 28.8 hours | 9.46 gal | 864,794 Btu |
| 100 lb | 72.1 hours | 23.64 gal | 2,161,986 Btu |
What to know about 100 lb tanks
- Heating. A 30,000 Btu/h heater running half the time on its thermostat would stretch the same tank to about six days.
- Generators. At Champion’s 3500 W dual-fuel generator’s rate of about 1.9 lb an hour at half load, a 100 lb tank is about 52 hours — see how long a generator runs on a 20 lb propane tank.
- Several appliances. Add the Btu ratings of everything that runs at once — heater, water heater, stove — for the combined burn.
- Vapor in the cold. A bigger tank keeps up with larger loads in cold weather far better than a 20 lb cylinder.
A 20 lb cylinder on a heater is on how long a 20 lb propane tank lasts for heating; on a grill, how long a 20 lb propane tank lasts on a grill. All the sizes are in the propane tank size chart.
Different size? Use the full Propane Tank Runtime Calculator.
What you’ll need
- 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 100 lb propane tank last at 50,000 Btu?
About 43.2 hours (43 h 14 min).
How long will a 100 lb propane tank last at 20,000 Btu?
About 108.1 hours (4.5 days).
How long will a 100 lb propane tank last for heating on a thermostat?
About 6 days for a 30,000 Btu/h heater running half the time.
Other common sizes
- How long a 20 lb propane tank lasts for heating — 24 hours at 18,000 Btu/h
- How long a 20 lb propane tank lasts on a grill — 14.4 hours at 30,000 Btu/h
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).
- 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.