Calculate how much propane weighs from gallons (about 4.24 lb per gallon), convert pounds to gallons, or estimate fuel left from a tank gauge or scale.
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Propane Weight Formula
An approximate reference calculation for liquid propane at 60°F (15.56°C) is:
W is net fuel weight in pounds and V is liquid volume in US gallons. The 4.24 lb/US gal reference is an approximate density, not a value derived from molecular weight alone or a universal billing rule. The temperature option separately uses historical saturated pure propane data; a verified custom density can represent the actual liquid temperature and composition.
Propane Liquid Density by Temperature
Liquid propane density varies with temperature and composition. The following historical saturated pure propane values come from NBS Letter Circular 736 (1943), Table 1, pp.14–17. The calculator linearly interpolates these retained points only between −40 and 110°F, and rejects values outside that range. This planning approximation is separate from the approximate 4.24 lb/US gal reference and is not a modern mixture equation or custody-transfer correction.
| Temperature (°F) | Temperature (°C) | Density (kg/L) | Density (lb/US gal) |
|---|---|---|---|
| -40 | -40.00 | 0.5782 | 4.8253 |
| -20 | -28.89 | 0.5653 | 4.7177 |
| 0 | -17.78 | 0.5519 | 4.6058 |
| 20 | -6.67 | 0.5378 | 4.4882 |
| 32 | 0.00 | 0.5290 | 4.4147 |
| 40 | 4.44 | 0.5230 | 4.3646 |
| 60 | 15.56 | 0.5072 | 4.2328 |
| 70 | 21.11 | 0.4988 | 4.1627 |
| 80 | 26.67 | 0.4901 | 4.0901 |
| 90 | 32.22 | 0.4811 | 4.0150 |
| 100 | 37.78 | 0.4716 | 3.9357 |
| 110 | 43.33 | 0.4615 | 3.8514 |
At a fixed net fuel mass, cooling increases liquid density and reduces liquid volume, so a volume gauge can read lower without fuel being removed. Warming does the reverse. The rate is not a fixed 1.5% per 10°F over all temperatures. Invoice temperature compensation depends on the actual product, measurement method and billing rules; this calculator does not certify it.
Common Propane Tank and Cylinder Weights
Portable cylinder ratings describe nominal fuel mass, while stationary tank labels commonly state total water capacity. Use the actual rated capacity and stamped tare weight for the specific equipment. Scale minus comparable actual tare estimates net fuel; attached hardware and measurement uncertainty matter. The tare weights below are illustrative examples, not preset measurements for an individual cylinder.
How to calculate full or empty cylinder weight
Loaded cylinder weight = empty cylinder weight (TW) + net propane weight. Choose Full or empty cylinder weight and enter the tare weight (TW) stamped on the cylinder. For a nominal full cylinder, enter its rated propane weight. If the supplier labels a lower net weight, enter that amount instead. Enter zero propane for the empty weight. The estimated liquid volume divides the net propane weight in pounds by 4.24 lb per US gallon.
For example, a cylinder marked TW 16.6 lb with a 20 lb propane fill weighs 36.6 lb in total. The propane itself is about 4.72 US gallons at the reference density.
| Tank / Cylinder | Propane Capacity (lbs) | Propane Capacity (gal) | Tare Weight (lbs) | Full Weight (lbs) | Model BTU at Listed Fuel Mass | Typical Use |
|---|---|---|---|---|---|---|
| 1 lb canister | 1.00 | 0.24 | 0.3 | 1.30 | 21,548 | Camping stoves |
| 5 lb cylinder | 5.00 | 1.18 | 7.0 | 12.00 | 107,740 | Small grills, torches |
| 11 lb cylinder | 11.00 | 2.59 | 12.0 | 23.00 | 237,028 | Tabletop grills, heaters |
| 20 lb cylinder | 20.00 | 4.72 | 17.0 | 37.00 | 430,960 | BBQ grills, patio heaters |
| 30 lb cylinder | 30.00 | 7.08 | 25.0 | 55.00 | 646,440 | RVs, large grills |
| 33 lb forklift | 33.00 | 7.78 | 28.0 | 61.00 | 711,084 | Forklifts |
| 40 lb cylinder | 40.00 | 9.43 | 32.0 | 72.00 | 861,920 | Food trucks, generators |
| 100 lb cylinder | 100.00 | 23.58 | 70.0 | 170.00 | 2,154,800 | Whole-house backup |
| 120 gal tank | 407.04 | 96.00 | 200 | 607.04 | 8,770,898 | Seasonal heating supplement |
| 250 gal tank | 848.00 | 200.00 | 483 | 1,331.00 | 18,272,704 | Primary home heating |
| 500 gal tank | 1,696.00 | 400.00 | 949 | 2,645.00 | 36,545,408 | Large homes, commercial |
| 1,000 gal tank | 3,392.00 | 800.00 | 1,760 | 5,152.00 | 73,090,816 | Commercial, agricultural |
The stationary-tank rows use an illustrative 80% of water capacity and the approximate 4.24 lb/US gal reference; cylinder rows use listed rated fuel mass. Their energy figures use 21,548 BTU/lb. These arithmetic examples do not establish a permitted fill level or equipment weight. Confirm the actual tank rating, temperature, product and applicable filling procedure with the supplier.
Why the 80% Fill Rule Exists
Containers require expansion space as liquid warms. A simple 80% volume target is a common planning example, not a universal legal filling limit. OSHA 1910.110 distinguishes filling density by mass and includes product, temperature and container qualifications. The calculator compares an optional supplier-approved target; it does not authorize filling. Colder liquid generally has higher density and lower volume for the same mass.
Propane Energy Content and Fuel Comparisons
The calculator’s editable energy basis is the approximate 21,548 BTU/lb total heating value in PERC’s Technical Pocket Guide, Table 1A. Energy = net fuel mass × this gross/HHV planning basis. The comparison table below uses separate rounded fuel reference values; heating values vary with product and basis, so its rounded volume figures need not equal a density-based calculation exactly. Runtime divides fuel energy by constant fuel-input rate on the same basis; it excludes reserve fuel, cycling, losses and vaporization limits.
| Fuel | BTU per Unit | Unit | BTU per Pound | Fuel Amount Equivalent to 1 US Gal Propane |
|---|---|---|---|---|
| Propane (liquid) | 91,500 | gallon | 21,548 | 1.00 |
| Natural gas | 100,000 | therm (100,000 BTU) | 23,000 | 0.92 therms |
| #2 Heating oil | 138,500 | gallon | 19,500 | 0.66 |
| Kerosene | 135,000 | gallon | 19,800 | 0.68 |
| Gasoline | 120,000 | gallon | 20,000 | 0.76 |
| Diesel | 139,000 | gallon | 19,300 | 0.66 |
| Electricity | 3,412 | kWh | n/a | 26.8 kWh |
Fuel-energy equivalence alone does not determine heating cost. Compare price per unit divided by heating value and actual appliance efficiency; for a heat pump, use its applicable coefficient of performance. Prices and performance vary. A therm is 100,000 BTU; its gas volume varies with actual heat content, as explained by EIA’s unit guidance. Theoretical runtime is not a guaranteed duration or proof of appliance delivery capacity.
Key Physical Properties of Propane
Propane (C3H8) is a three-carbon alkane that exists as a gas at standard atmospheric conditions but liquefies easily under moderate pressure or refrigeration. The properties below define its behavior in storage, transport, and combustion.
| Property | Value |
|---|---|
| Molecular formula | C3H8 |
| Molecular weight | 44.097 g/mol |
| Boiling point | -44 °F (-42.1 °C) |
| Vapor pressure at 100 °F | Approximately 196 psig (1.35 MPa gauge), PERC pure propane at 100°F |
| Liquid density at 60 °F | 4.24 lb/gal (0.508 kg/L) |
| Gas density at 60 °F, 1 atm | 0.1162 lb/ft3 |
| Vapor specific gravity (air = 1) | 1.52 |
| Liquid expansion rate | Varies with temperature; no fixed rate used |
| Liquid-to-gas expansion ratio | 270:1 at 60 °F |
| Flash point | -156 °F (-104 °C) |
| Autoignition temperature | Approximately 920–1,120°F (493–604°C), PERC range |
| Flammable range in air | 2.1% to 9.5% by volume |
| Octane number (RON) | 112 |
| Heat of combustion | 91,500 BTU/gal or 2,516 BTU/ft3 |
| Flame temperature in air | 3,595 °F (1,980 °C) |
Propane vapor is denser than air, and a liquid leak can expand into a much larger vapor volume. The table lists approximate reference properties, not detector-placement or equipment-operating instructions. Follow the detector manufacturer’s instructions and supplier guidance for the specific installation. This liquid calculator does not model a leak, flammable cloud or vaporization capacity.
How to Read Your Propane Tank Gauge
Tank gauges vary; confirm that the reading represents liquid percentage of stated water capacity. For example, 500 US gallons × 40% = approximately 200 US gallons of liquid; at the 4.24 reference that is about 848 lb. The 21,548 BTU/lb model gives about 18.27 million BTU. Gauge and thermal effects make this an estimate. Any refill comparison uses measured added mass divided by approximate 4.24 lb/US gal to estimate a 60°F equivalent; it cannot by itself establish short filling, billing accuracy or a permitted delivery quantity.
