Propane Refill Cost Calculator
Work out what a propane refill costs: the gallons or pounds to add from a gauge reading or a scale weight, the 80% fill limit, price per gallon, liter, pound or kilogram, delivery fees, minimums and tax, a budget check, and how a refill compares with a tank exchange.
How it works
Tank volume = the nominal size for stationary tanks, or rated pounds ÷ 4.24 lb/gal ÷ 0.8 for cylinders · Propane now = volume × gauge % (or (scale weight − tare) ÷ 4.24 lb/gal) · Gallons to add = volume × target % − propane now · Refill cost = max(gallons to add, minimum) × price per gallon × (1 + tax) + fixed fees
Propane is sold by volume or weight, so a refill costs the propane you add times the unit price, plus any delivery fee and tax. The trick is knowing how much fits. Containers are never filled completely: liquid propane expands as it warms, so the safe limit is about 80% of the tank’s total (water) volume. Stationary tank gauges read a share of that total volume, which is why a freshly filled 500-gallon tank shows 80% and holds about 400 gallons. Portable cylinders are rated by the pounds of propane they hold when properly filled — 20 lb is about 4.7 gallons at 4.24 lb per gallon — and the calculator treats that rated weight as the 80% mark. If your cylinder has no gauge, weigh it: the scale weight minus the tare (the TW stamped on the collar) is the propane left. Enter the price in whatever unit the station uses — per gallon, liter, pound or kilogram — and add fees, a minimum bill or sales tax under More options. For a 20 lb grill cylinder the calculator also compares a refill with a store exchange, which usually contains only 15 lb of propane, and the tables show the cost from other starting levels and for other tank sizes.
Worked example
A 20 lb grill cylinder holds about 4.72 gallons when full, so its total volume is 4.72 ÷ 0.8 = 5.90 gallons. At 15% on the gauge it still holds 5.90 × 15% = 0.88 gallons; filling to 80% adds 5.90 × 80% − 0.88 = 3.83 gallons (16.2 lb). At $3.50 a gallon the refill costs about $13.41. A $24.99 exchange cylinder holding 15 lb (3.54 gallons) works out to $7.06 a gallon, so refilling the same amount would cost $12.38 — about half.
Sources: NFPA 58 — Liquefied Petroleum Gas Code (overview) · U.S. EIA — Heating oil and propane update (weekly residential prices) · Propane Education & Research Council — propane facts
Frequently asked questions
Is refilling cheaper than exchanging the tank?
Usually. Refill stations charge for the propane actually pumped, while exchange cages charge a flat price for a cylinder that typically holds 15 lb rather than 20. Per gallon, an exchange often costs 40–100% more. Exchanges win on convenience, and they replace an old cylinder without you paying for requalification.
Why can’t a tank be filled to 100%?
Liquid propane expands roughly 1.5% for every 10 °F (5.5 °C) it warms, so tanks are filled to about 80% of their volume to leave a vapor space. Overfilling can make the relief valve vent propane on a hot day, which is why attendants stop at the 80% fixed liquid-level (bleeder) valve.
How do I know my current level?
Weigh the cylinder: subtract the tare (TW) weight stamped on the collar from the scale reading to get the pounds of propane left — choose Scale weight and the calculator does it. A 20 lb cylinder with a 17 lb tare that weighs 22 lb has 5 lb (1.2 gallons) left. Stationary tanks have a float gauge that reads the percentage directly.
How many gallons does a 20 lb propane tank hold?
About 4.7 gallons (17.9 liters) when full, because propane weighs about 4.24 lb per gallon at 60 °F. A 30 lb cylinder holds about 7.1 gallons, a 40 lb about 9.4 and a 100 lb about 23.6.
How much does it cost to fill a 500-gallon propane tank?
From empty to the 80% limit it takes about 400 gallons, but tanks are normally refilled from 20–30%, which takes 250–300 gallons. Multiply by your supplier’s price and add any delivery fee — choose the 500 gal tank, enter your gauge reading and the calculator shows the exact figure.
Why does my bill show different gallons from the calculator?
Gauges are only accurate to a few percent, propane volume changes with temperature, and some meters correct to 60 °F. Stations may also round up or charge a minimum, and cylinders that were partly full may take less than expected.
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This calculator is for educational purposes. Double-check important results before acting on them.