How much propane do you have, and how long will it last?
Read the tank gauge, convert pounds and gallons, or find the days an appliance can run on a tank.
A tank's size is its water capacity; it is filled to about 80% of that with propane.
Pounds of propane, not the cylinder's total weight with its steel.
Total input of everything that runs: add the BTU/h of each appliance. Take the hours it really fires, not the hours it is switched on.
An example price: use your supplier's. Clear the box to hide the money lines.
How do I know how many gallons are in my propane tank?
Read the gauge: it shows the percentage of the tank's volume that is liquid propane. Multiply it by the tank's size, which is its water capacity: 40% on a 500-gallon tank is 0.40 × 500 = 200 gallons. Tanks are normally filled to about 80% of their capacity to leave room for the liquid to expand, so a 500-gallon tank holds up to roughly 400 gallons of propane. The regulation 29 CFR 1910.110 works the same limit out for a 100-gallon tank at 79.8 gallons.
How many pounds is a gallon of propane?
About 4.2 pounds at 60 °F; the NIST Chemistry WebBook gives 4.23 for pure propane. So 20 lb of propane is about 4.8 gallons, and 100 gallons weigh about 420 lb. A “20 lb” cylinder holds at most 20 lb, and NIST notes that most are filled and labeled to a net 15 lb, about 3.6 gallons.
How much energy is in a gallon of propane?
The EIA puts it at 91,452 BTU per gallon, the gross (higher) heating value, and the heating cost calculator on this site uses the same number. The Alternative Fuels Data Center lists 91,420 BTU as the higher and 84,250 BTU as the lower heating value, which leaves out the heat in the water vapor of the exhaust. A gallon of propane at 91,452 BTU is 26.8 kWh of heat.
How long will a tank of propane last?
Gallons an hour = the appliance's BTU/h input ÷ 91,452. A 75,000 BTU/h heater burns 75,000 ÷ 91,452 = 0.82 gallons an hour at full input; at 8 hours a day that is 6.6 gallons a day, so 100 gallons last about 15 days. A 30,000 BTU/h range burns 0.33 gallons an hour. Take the input rating from the appliance's nameplate and the hours it actually fires, since a thermostat-controlled appliance runs less than the clock.
What should I do if I smell propane?
The Propane Education & Research Council's guide for portable cylinders says: no smoking, vaping or open flames; if there are no flames or visible cloud of propane at the cylinder, close the cylinder valve; leave the area, then call 911 or the fire department. Propane is heavier than air and can settle near the ground, and a cylinder should never be used or stored in an enclosed area such as a basement, garage or shed. This calculator only estimates amounts; for any doubt about a tank or appliance, call your propane supplier or a qualified professional.
Sources: U.S. EIA, Monthly Energy Review, Appendix A (BTU conversion factors); U.S. DOE Alternative Fuels Data Center, Fuel Properties Comparison; NIST Chemistry WebBook (propane saturation properties) and NIST Measurement Matters, “Liquified Petroleum Gas 20 Pound Cylinders” (July 2021); OSHA 29 CFR 1910.110; Propane Education & Research Council, “Dispensing Propane Safely into Agricultural Equipment” and “Safety Guide for Portable Propane Cylinders”; Manchester Tank, aboveground propane storage tanks (2024); Worthington, steel portable cylinders (2025). Compare fuels: heating cost calculator. Sizing a furnace: furnace size calculator. How we check our calculators.