Propane Tank Size Calculator

One US gallon of HD-5 propane delivers about 91,500 BTU at standard conditions (NIST and the National Propane Gas Association both publish 91,502 BTU as the gross higher heating value). That means a 250 gallon tank filled to its usable 200 gallons stores roughly 18.3 million BTU. The calculator divides your total annual BTU load by 91,500 to find gallons per year, so any appliance rating you can find on a nameplate or spec sheet plugs straight in.

Liquid propane expands roughly 17 times more than water for the same temperature change, so a tank topped to 100 percent in cool morning weather can build dangerous pressure by afternoon. NFPA 58 (the US LPGA code) caps fill volume at about 80 percent of water capacity to leave headroom for that thermal expansion. The standard tank sizes in this calculator already report the usable 80 percent figure: a 250 gallon water-capacity tank holds 200 usable gallons, a 500 gallon tank holds 400, and so on.

The common options run from the 20 lb grill bottle (about 5 usable gallons) up to a 1,000 gallon stationary tank (800 usable gallons). In between are 100 lb portable cylinders (24 gallons), and stationary tanks at 120 gallons (96 usable), 250 (200 usable), and 500 (400 usable). Most whole-home setups use 250 or 500 gallon tanks: 500 gallon is the workhorse for cold-climate furnace plus water heater plus range, while 250 is enough for a single heating appliance or a summer cabin.

Use these defaults when you do not have a nameplate handy. A tank water heater runs 40,000 BTU/hr. A residential furnace ranges from 60,000 BTU/hr in a small efficient home to 100,000+ in a large or cold-climate home. A propane range averages 65,000 BTU/hr across all burners and the oven. A clothes dryer pulls about 22,000 BTU/hr. A fireplace insert lands around 30,000 BTU/hr, and a generator at full load can hit 80,000 BTU/hr. Multiply the BTU/hr by realistic hours of daily use, not nameplate hours, since most appliances cycle on and off.

Almost always, yes. A larger tank means fewer delivery trips per year, and most propane suppliers offer a bulk-fill discount once you order 200 or 300+ gallons at once. Stepping from a 250 to a 500 gallon tank typically cuts annual deliveries from 3 or 4 down to 1 or 2 and unlocks 10 to 30 cent per gallon savings. The upfront installation cost difference is $300 to $700 and the larger tank also carries you through a cold snap if your supplier is behind on routes. The calculator's default 20 percent safety margin gives you buffer for that cold snap; bump it to 30 or 40 percent if you live somewhere a stuck delivery truck is a real risk.