Gallons to Pounds Converter
Convert gallons of water or any liquid into pounds by adjusting density. Essential for engineering, plumbing, cooking, aquariums, chemistry, fuel, and industrial measurements.
What the gallons to pounds converter does
The gallons to pounds converter turns a volume of liquid into its weight. Enter the number of US gallons and the density of the liquid in pounds per gallon, then press Calculate. The default density of 8.34 lb/gal is fresh water at room temperature; change it for any other liquid using the table below.
The formula
pounds = gallons × density (lb/gal)
Weight depends on what is in the container, which is why a gallon of gasoline (about 6.1 lb) is much lighter than a gallon of water (8.34 lb) and both are lighter than a gallon of honey (about 12 lb).
Densities of common liquids
| Liquid | lb per US gallon | kg per litre |
|---|---|---|
| Gasoline | 6.1 | 0.73 |
| Diesel | 7.1 | 0.85 |
| Ethanol | 6.6 | 0.79 |
| Vegetable oil | 7.7 | 0.92 |
| Fresh water (20 °C) | 8.34 | 1.00 |
| Seawater | 8.56 | 1.03 |
| Whole milk | 8.6 | 1.03 |
| Antifreeze (ethylene glycol) | 9.3 | 1.11 |
| Honey | 11.8 to 12.0 | 1.42 |
| Sulfuric acid (98%) | 15.3 | 1.84 |
| Mercury | 113 | 13.5 |
To convert kg/L to lb/gal, multiply by 8.345. Densities change slightly with temperature; water at 80 °C is 8.1 lb/gal.
Worked examples
Fuel tank. A 20-gallon gasoline tank when full holds 20 × 6.1 = 122 lb of fuel. The same tank of diesel weighs 142 lb.
Aquarium. A 55-gallon freshwater tank holds 55 × 8.34 = 459 lb of water before the glass, gravel and stand. This is why large tanks need a checked floor and a purpose-built stand.
Hot tub. 400 gallons of water is 3,336 lb, about 1.5 tonnes.
Boat trailer. 30 gallons of fresh water in the tanks adds 250 lb to the towed weight.
US versus imperial gallons
The converter uses the US gallon of 3.785 L. The imperial gallon used in the UK is 4.546 L, about 20% larger, and a gallon of water in that system weighs 10.02 lb. If your figure comes from a British source, multiply the gallons by 1.201 before entering them, or enter a density of 10.02 for water.
From weight to volume
Rearrange to gallons = pounds ÷ density. A 50 lb bag-in-box of syrup at 11 lb/gal is 4.5 gallons. The kg to gallons converter works in metric weight, and the density converter changes units between lb/gal, kg/L and g/mL.
Common mistakes
- Using the water density for every liquid. Fuel, oil and alcohol are 10 to 27% lighter; syrups and acids are heavier.
- Mixing US and imperial gallons. The 20% difference is large enough to overload a trailer or a floor.
- Ignoring temperature for fuel. Fuel density falls about 1% per 10 °C rise, which matters for aircraft and bulk shipments.
- Forgetting the container. Drums, tanks and bottles add weight the calculator does not include.
Related tools
The volume converter and weight converter handle unit changes on each side of the formula. The cubic feet calculator and cubic metre calculator find the volume of a tank from its dimensions (1 ft³ = 7.48 US gal), and the CCF to gallons converter reads water meters.
External references
Frequently asked questions
How much does a gallon of water weigh?
8.34 lb for a US gallon at room temperature, 10.02 lb for an imperial gallon.
How much does a gallon of gasoline weigh?
About 6.1 lb, varying between 5.9 and 6.3 lb depending on blend and temperature.
How much does a gallon of milk weigh?
About 8.6 lb. Skimmed milk is slightly denser than whole milk because fat is lighter than water.
Where do I find the density of a chemical?
The safety data sheet lists specific gravity. Multiply specific gravity by 8.345 to get lb per US gallon.
Does the calculator handle other volume units?
Convert to gallons first with the volume converter, or convert the density to match: for litres, use kg/L and read the answer as kilograms.