Propane Tank Calculator
Find how much propane is in a tank — from a 1 lb canister to a 1,000-gallon tank — and how long it will last: gallons, pounds and BTU left, burn rate, run time at full or partial burner setting, days at your daily use, and a size-by-size comparison.
How it works
Usable gallons = rated pounds ÷ 4.24 lb/gal for cylinders, or 80% of the nominal size for stationary tanks · Gallons remaining = usable gallons × fill % (a gauge reading ÷ 80% first) · Energy = gallons × 91,500 BTU/gal · Burn time (hours) = energy ÷ appliance BTU/hr ÷ average setting · Days = burn time ÷ hours used per day
Propane holds about 91,500 BTU of energy per gallon, so a tank’s run time is the energy left in it divided by how fast the appliance burns it. Portable cylinders are named for the pounds of propane they hold: at 4.24 lb per gallon a 20 lb grill tank holds about 4.7 gallons, a 100 lb tank about 23.6. Stationary tanks are named for their total volume but are only filled to about 80% to leave room for the liquid to expand, so a 500-gallon tank holds about 400 gallons and its gauge reads 80% when full — choose “Gauge reading” to enter the number on the dial as it is. The headline figure assumes the appliance runs continuously at its full rated BTU. Set an average burner setting to reflect a grill on medium or a heater that cycles on a thermostat, and enter hours per day to see how many days the tank lasts and a day-by-day chart of what is left. The size table compares every common tank at your appliance’s rating, so you can see what a bigger tank would buy you. For the cost of a refill use the propane refill cost calculator; for an appliance’s running cost per day or month use the propane usage cost calculator.
Worked example
A full 20 lb grill tank holds 20 ÷ 4.24 = 4.72 gallons × 91,500 = 431,604 BTU. A 30,000 BTU/hr grill running wide open uses it up in 431,604 ÷ 30,000 ≈ 14.4 hours (14 h 23 m). Grilling 4 hours a day at full fire, that is about 3.6 days. A 500-gallon tank whose gauge reads 60% holds 400 × 75% = 300 gallons — about 27.5 million BTU, or 38 days of an 80,000 BTU/hr furnace running 9 hours a day.
Sources: U.S. EIA — Energy units and calculators (heat content of propane) · NFPA 58 — Liquefied Petroleum Gas Code (overview)
Frequently asked questions
How many BTU does a gallon of propane hold?
About 91,500 BTU per gallon, or roughly 21,600 BTU per pound (24,200 BTU per liter). A full 20 lb grill cylinder holds about 4.7 gallons — some 430,000 BTU — which is the figure this calculator converts into run time.
How long does a 20 lb propane tank last?
About 14 hours on a 30,000 BTU/hr burner running flat out, 18 hours at 24,000 BTU/hr and about 10.8 hours on a 40,000 BTU/hr patio heater. Grilling on medium roughly doubles those times, so a tank typically lasts many weekends of cooking.
Why does my tank last longer than the estimate?
The estimate assumes the appliance runs continuously at its maximum rated BTU. Most burners cycle: a patio heater or furnace on a thermostat, or a grill on medium, draws full gas only part of the time. Enter an average burner setting below 100% to model that.
Why is a 500-gallon tank only 400 usable gallons?
Large propane tanks are filled to about 80% of capacity to leave room for the liquid to expand as temperature rises — a safety requirement. So a 500-gallon tank holds around 400 gallons, a 250 about 200 and a 1,000 about 800. Their gauges read 80% when full.
What size propane tank do I need?
Match the tank to your yearly use and how often you want deliveries. A 120-gallon tank suits a water heater or range alone; 250–325 gallons a small home with a few appliances; 500 gallons whole-home heating for a typical house; 1,000 gallons large homes or farms. Use the size table with your appliance’s BTU rating to compare run times.
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This calculator is for educational purposes. Double-check important results before acting on them.