Propane Tank Size Chart: Gallons, BTU, Weight & Runtime 2026

How long does a 20-lb propane tank last?

On the defaults — a 20-lb tank on a 30,000 BTU-per-hour grill — the answer is 14.03 hours, or 0.58 days. One gallon of propane holds 91,502 BTU of energy and weighs 4.24 pounds; propane tanks are filled to only 80% of their water capacity, which is why a “20-pound” tank holds 4.6 gallons instead of 4.7; the pound sizes are the weight of the propane inside — a 20-lb tank weighs about 37 pounds full, because the steel tank itself weighs about 17 pounds; the gallon sizes are the tank’s capacity in gallons — a 500-gallon home tank holds about 400 gallons when filled to 80%; a standard gas grill burner runs about 25,000–30,000 BTU an hour, a patio heater about 40,000–50,000, and a home furnace 60,000–100,000 or more; never store a propane tank indoors or in a closed garage, and never fill one past 80% — liquid propane expands as it warms.

Five things about the model are worth stating plainly. First, the total BTU is the gallons times 91,502 BTU per gallon — 4.6 × 91,502 = 420,909. Second, the runtime in hours is the total BTU divided by the appliance’s BTU per hour — 420,909 ÷ 30,000 = 14.03. Third, the runtime in days is the hours divided by 24 — 0.58. Fourth, the BTU is printed as a whole number, nearest BTU. And fifth, an appliance rate of zero or below is an input error, not a result — the calculator shows an error; all listed in Accuracy & limitations.

The full tank chart

Total BTU = gallons × 91,502 BTU per gallon. Runtime = total BTU ÷ appliance BTU per hour. A 20-lb tank holds 4.6 gallons and 420,909 BTU; a 100-lb tank holds 23.6 gallons and 2,159,447 BTU; a 500-gallon home tank holds 45,751,000 BTU.

The worked example, line by line

Setup: 20-lb tank, 30,000 BTU per hour.

Line 1 — the gallons. A 20-lb tank holds 4.6 gallons at an 80% fill.

Line 2 — the total BTU. 4.6 × 91,502 = 420,909 BTU.

Line 3 — the runtime in hours. 420,909 ÷ 30,000 = 14.03 hours.

Line 4 — the runtime in days. 14.03 ÷ 24 = 0.58 days.

Line 5 — the check. A 100-lb tank holds 23.6 gallons and 2,159,447 BTU, so the same grill runs 71.98 hours.

Line 6 — the big tank. A 500-gallon home tank holds 45,751,000 BTU, so on a 30,000 BTU appliance it runs 1,525.03 hours.

Line 7 — the furnace. A 120-gallon tank on a 100,000 BTU furnace runs 109.80 hours.

Every branch, checked

30 lb at 30,000 BTU/h: Tank 30 lb — 7.0 gallons, 640,514 BTU, runs 21.35 hours (0.89 days) — A 30-lb tank runs 21.35 hours on the same grill — seven more hours than the 20-lb tank, and still short of a full day.

100 lb at 30,000 BTU/h: Tank 100 lb — 23.6 gallons, 2,159,447 BTU, runs 71.98 hours (3.00 days) — The 100-lb tank is the first one that clears three days on a grill: 71.98 hours, or 3.00 days.

20 lb at 50,000 BTU/h: Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 8.42 hours (0.35 days) — A patio heater at 50,000 BTU an hour drains the 20-lb tank in 8.42 hours — less than one evening of steady heat.

500 gal at 30,000 BTU/h: Tank 500 gal — 500 gallons, 45,751,000 BTU, runs 1,525.03 hours (63.54 days) — The 500-gallon home tank is 1,525.03 hours on a 30,000 BTU appliance — 63.54 days, or about two months of steady use.

120 gal at 100,000 BTU/h: Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 109.80 hours (4.58 days) — A 120-gallon tank on a 100,000 BTU furnace runs 109.80 hours — 4.58 days of heat from one fill.

40 lb at 15,000 BTU/h: Tank 40 lb — 9.4 gallons, 860,119 BTU, runs 57.34 hours (2.39 days) — A small 15,000 BTU heater stretches the 40-lb tank to 57.34 hours — 2.39 days.

1000 gal at 200,000 BTU/h: Tank 1000 gal — 1000 gallons, 91,502,000 BTU, runs 457.51 hours (19.06 days) — The biggest tank on the biggest appliance: a 1000-gallon tank at 200,000 BTU an hour runs 457.51 hours, or 19.06 days.

The reverses, worked backwards

Smallest tank for at least 24 hours at 30,000 BTU/h: At the displayed 40 lb the figures are Tank 40 lb — 9.4 gallons, 860,119 BTU, runs 28.67 hours (1.19 days) at 30,000 BTU/h. The 30-lb tank gives only 21.35 hours — below 24 — so the 40-lb tank at 28.67 hours is the smallest that clears a full day.

Largest whole BTU/h for a 20-lb tank to run at least 20 hours: At the displayed 21,045 BTU/h the figures are Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 20.0004 hours (unrounded) at 21,045 BTU/h. Both 21,045 and 21,046 BTU/h display as 20.00 hours, so the unrounded runtimes decide it: 20.0004 hours against 19.9995 hours.

Smallest tank for at least 100 hours at 50,000 BTU/h: At the displayed 120 gal the figures are Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 219.60 hours (9.15 days) at 50,000 BTU/h. The 100-lb tank gives only 43.19 hours at 50,000 BTU/h — below 100 — so the 120-gallon tank at 219.60 hours is the smallest that clears it.

Smallest tank for at least 1,000,000 BTU: At the displayed 100 lb the figures are Tank 100 lb — 23.6 gallons, 2,159,447 BTU. The 40-lb tank holds only 860,119 BTU — below 1,000,000 — so the 100-lb tank at 2,159,447 BTU is the smallest that clears a million.

Appliance BTU/h for a 500-gallon tank to last exactly 720 hours (30 days): At the displayed 63,543.06 BTU/h the figures are Tank 500 gal — 500 gallons, 45,751,000 BTU, runs 720.00 hours (719.9999… hours unrounded) at 63,543.06 BTU/h. The exact rate is 63,543.0556 BTU/h, displayed 63,543.06 BTU/h; the forward at the displayed rate is 720.00 hours (719.9999… hours unrounded); at 63,544 BTU/h the runtime is 719.99 hours.

Smallest tank for a 100,000 BTU/h furnace to run 100 hours: At the displayed 120 gal the figures are Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 109.80 hours (4.58 days) at 100,000 BTU/h. The 100-lb tank gives only 21.59 hours on a 100,000 BTU/h furnace — below 100 — so the 120-gallon tank at 109.80 hours is the smallest that clears it.

What the defaults assume

The defaults are the 20-lb tank on a 30,000 BTU-per-hour appliance — Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 14.03 hours (0.58 days) at 30,000 BTU/h. With 30 lb at 30,000 BTU/h, Tank 30 lb — 7.0 gallons, 640,514 BTU, runs 21.35 hours (0.89 days). With 100 lb at 30,000 BTU/h, Tank 100 lb — 23.6 gallons, 2,159,447 BTU, runs 71.98 hours (3.00 days). With 20 lb at 50,000 BTU/h, Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 8.42 hours (0.35 days). With 500 gal at 30,000 BTU/h, Tank 500 gal — 500 gallons, 45,751,000 BTU, runs 1,525.03 hours (63.54 days). With 120 gal at 100,000 BTU/h, Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 109.80 hours (4.58 days). With 40 lb at 15,000 BTU/h, Tank 40 lb — 9.4 gallons, 860,119 BTU, runs 57.34 hours (2.39 days). With 1000 gal at 200,000 BTU/h, Tank 1000 gal — 1000 gallons, 91,502,000 BTU, runs 457.51 hours (19.06 days). With Appliance 0 BTU/h, Input error — the rate must be above 0 (the calculator shows an error, not a result). With 1000 gal at 30,000 BTU/h, Tank 1000 gal — 1000 gallons, 91,502,000 BTU, runs 3,050.07 hours (127.09 days). With 20 lb at 10,000 BTU/h, Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 42.09 hours (1.75 days). With 250 gal at 400,000 BTU/h, Tank 250 gal — 250 gallons, 22,875,500 BTU, runs 57.19 hours (2.38 days). With 120 gal at 30,000 BTU/h, Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 366.01 hours (15.25 days). With 20 lb at 100,000 BTU/h, Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 4.21 hours (0.18 days). With 100 lb at 91,502 BTU/h (exactly one gallon an hour), Tank 100 lb — 23.6 gallons, 2,159,447 BTU, runs 23.60 hours (0.98 days).

Appliance 0 BTU/h: Input error — the rate must be above 0 (the calculator shows an error, not a result).

1000 gal at 30,000 BTU/h: Tank 1000 gal — 1000 gallons, 91,502,000 BTU, runs 3,050.07 hours (127.09 days).

20 lb at 10,000 BTU/h: Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 42.09 hours (1.75 days).

250 gal at 400,000 BTU/h: Tank 250 gal — 250 gallons, 22,875,500 BTU, runs 57.19 hours (2.38 days).

120 gal at 30,000 BTU/h: Tank 120 gal — 120 gallons, 10,980,240 BTU, runs 366.01 hours (15.25 days).

20 lb at 100,000 BTU/h: Tank 20 lb — 4.6 gallons, 420,909 BTU, runs 4.21 hours (0.18 days).

100 lb at 91,502 BTU/h (exactly one gallon an hour): Tank 100 lb — 23.6 gallons, 2,159,447 BTU, runs 23.60 hours (0.98 days).

Output · formula · meaning

Who uses this

• The griller planning a cookout: they learn a 20-lb tank runs 14.03 hours on a 30,000 BTU grill — and they check the 30-lb row to see 21.35 hours for a longer day.
• The RVer sizing a heater: they learn a 40-lb tank runs 57.34 hours on a 15,000 BTU heater — and they check the 100-lb row to see 71.98 hours on the grill.
• The homeowner sizing a furnace tank: they learn a 120-gallon tank runs 109.80 hours on a 100,000 BTU furnace — and they check the 500-gallon row to see 1,525.03 hours on a 30,000 BTU appliance.
• The buyer comparing pound and gallon tanks: they learn the pound sizes are the weight of the propane inside and the gallon sizes are the tank capacity — and they check the 21,045 BTU/h reverse to see where a 20-lb tank stops lasting 20 hours.

Accuracy & limitations

The math is first-principles: total BTU is gallons times 91,502 BTU per gallon, printed as a whole number (nearest BTU); runtime hours are total BTU divided by appliance BTU per hour, rounded to two decimals; runtime days are hours divided by 24, rounded to two decimals. What the model cannot do is run your appliance at its nameplate rate all the time: a grill burner cycles, a furnace cycles harder on cold nights, and a tank in cold weather delivers less usable gas; the gallons are the 80% fill figures, not the water capacity; and the chart counts no regulator loss, no hose loss, and no pilot light. Use it to size the tank and the refill — then check the gauge before the cookout.

Frequently asked questions