LPG Weighs 4.2-4.7 Pounds per Gallon (U.S.) at 60°F
Liquefied petroleum gas (LPG)-primarily propane or butane-weighs 4.2-4.7 lbs per gallon (0.50-0.56 kg/L) in liquid form at 60°F (15°C). Weight varies slightly by propane-butane mix, temperature, and pressure. One gallon of LPG expands to ~36.39 cubic feet of gas when vaporized.
Key Factors Affecting LPG Weight per Gallon
- Composition: Pure propane (~4.23 lbs/gal) is lighter than butane (~4.81 lbs/gal).
- Temperature: Weight decreases ~0.1% per 1°F rise (liquid expands).
- Pressure: Higher pressure slightly increases density (minimal impact at standard conditions).
- Measurement system: U.S. gallons (3.785 L) vs. imperial gallons (4.546 L).
LPG Weight Comparison: Liquid vs. Gas Phase
| Phase | Weight per Gallon (U.S.) | Volume Expansion | Energy Content (BTU/gal) |
|---|---|---|---|
| Liquid LPG (60°F) | 4.2-4.7 lbs | 1 gallon = ~36.39 ft³ gas | ~91,500-95,000 |
| Vaporized LPG (atmospheric pressure) | 0.11-0.13 lbs/ft³ | 1 ft³ gas = ~0.028 gallons liquid | ~2,500-2,600 BTU/ft³ |
| Water (reference) | 8.34 lbs/gal | N/A | N/A |
How to Calculate LPG Weight for Tanks
- Check tank capacity: E.g., a 20-lb propane tank holds ~4.7 gallons (80% fill rule).
- Use density: Multiply gallons by 4.23 lbs/gal (propane) or 4.81 lbs/gal (butane).
- Account for temperature: Subtract 0.04 lbs/gal per 1°F above 60°F.
- Verify mix ratio: 70/30 propane-butane blend ≈ 4.4 lbs/gal.
Common LPG Container Weights
- 1-lb disposable cylinder: Holds ~0.24 gallons (1 lb LPG).
- 20-lb refillable tank: ~4.7 gallons (17-18 lbs LPG when full).
- 100-lb cylinder: ~23.8 gallons (80-85 lbs LPG).
- 500-gallon residential tank: ~2,100-2,350 lbs LPG (400-420 gallons max fill).
Safety Notes on LPG Weight
- Never fill tanks beyond 80% capacity (liquid expansion risk).
- LPG is 2x heavier than air in gas form (sinks, collects in low areas).
- Weight labels on tanks refer to LPG content only (excluding container weight).