Propane tank size chart: gallons, Btu and hours
Portable propane cylinders are sold by the pounds of propane they hold. This chart turns each common size into gallons, Btu and hours of burning at typical appliance ratings, using the EIA’s heat content for propane and NIST’s density for the liquid.
Propane tank sizes in gallons and Btu
| Tank | Gallons | Btu | kWh of heat |
|---|---|---|---|
| 1 lb | 0.24 | 21,620 | 6.3 |
| 5 lb | 1.18 | 108,099 | 31.7 |
| 11 lb | 2.6 | 237,818 | 69.7 |
| 20 lb | 4.73 | 432,397 | 126.7 |
| 30 lb | 7.09 | 648,596 | 190.1 |
| 40 lb | 9.46 | 864,794 | 253.5 |
| 100 lb | 23.64 | 2,161,986 | 633.6 |
So the familiar barbecue cylinder — a “20 lb tank” — holds about 4.7 gallons of propane, about 432,000 Btu of heat. A 100 lb cylinder holds five times that, about 23.6 gallons.
How many hours each tank lasts
| Tank | 5,000 Btu/h | 10,000 Btu/h | 20,000 Btu/h | 30,000 Btu/h | 50,000 Btu/h |
|---|---|---|---|---|---|
| 1 lb | 4.3 | 2.2 | 1.1 | 0.7 | 0.4 |
| 5 lb | 21.6 | 10.8 | 5.4 | 3.6 | 2.2 |
| 11 lb | 47.6 | 23.8 | 11.9 | 7.9 | 4.8 |
| 20 lb | 86.5 | 43.2 | 21.6 | 14.4 | 8.6 |
| 30 lb | 129.7 | 64.9 | 32.4 | 21.6 | 13 |
| 40 lb | 173 | 86.5 | 43.2 | 28.8 | 17.3 |
| 100 lb | 432.4 | 216.2 | 108.1 | 72.1 | 43.2 |
Common questions, worked through: how long a 20 lb propane tank lasts for heating, how long a 20 lb propane tank lasts on a grill and how long a 100 lb propane tank lasts. For a dual-fuel generator, see how long a generator runs on a 20 lb propane tank.
Where the numbers come from
- Energy per gallon: the EIA lists propane at 91,452 Btu per gallon. Dividing the Btu in a tank by an appliance’s Btu-per-hour rating gives hours at full rating.
- Weight per gallon: NIST’s data for saturated liquid propane gives about 31.6 lb per cubic foot at 60 °F — 4.23 lb per US gallon. Warm propane is less dense (about 4.09 lb per gallon at 80 °F), which is one reason tanks are filled and sold by weight.
- Pounds on the label: a “20 lb” cylinder holds 20 lb of propane when full. The cylinder’s own empty weight — the tare weight, stamped “TW” on the collar — is extra.
Checking how much is left
- Find the tare weight (TW) stamped on the cylinder’s collar.
- Weigh the cylinder on a bathroom or luggage scale.
- Subtract the tare weight: what is left is pounds of propane. Divide by 4.23 for gallons, or use it directly in the propane tank runtime calculator.
A gauge is quicker, but weighing is the honest check — especially before a cold night or a long outage.
Propane vs gasoline and electricity
| Energy store | Heat content |
|---|---|
| 1 gallon of propane | 91,452 Btu (≈ 26.8 kWh) |
| 1 gallon of gasoline | 120,214 Btu (≈ 35.2 kWh) |
| 1 gallon of diesel | 137,381 Btu (≈ 40.3 kWh) |
| A 1,000 Wh power station | 3,412 Btu (1 kWh) |
That comparison is why off-grid homes heat with propane, wood or diesel rather than batteries: a single 20 lb cylinder holds the heat of over a hundred kilowatt-hours, against one or two kilowatt-hours in a portable power station.
Frequently asked questions
How many gallons are in a 30 lb propane tank?
About 7.1 gallons when full (30 ÷ 4.23), roughly 649,000 Btu.
How many gallons in a 100 lb propane tank?
About 23.6 gallons, roughly 2.16 million Btu, when full.
How long does a 1 lb propane cylinder last?
About 21,600 Btu, so roughly 2.2 hours at 10,000 Btu/h, or about 4.3 hours at 5,000 Btu/h.
How much does a gallon of propane weigh?
About 4.23 lb at 60 °F, from NIST’s data for liquid propane; slightly less when warm.
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).