Convert gallons of water, milk, honey, fuel, oil or any liquid to pounds (and pounds back to gallons) in US or UK gallons. Choose a liquid or enter its density.
1 US gal of water ≈ 8.33 lb · 1 UK gal ≈ 10.0 lb
Gallons measure volume and pounds measure weight, so you need the liquid's density to link them. If you know the density in kilograms per litre, which is the same number as its specific gravity, use the factor for your gallon:
8.3454 is a US gallon (3.785411784 L) divided by the kilograms in a pound (0.45359237), so it is exact. It is what a gallon would weigh at exactly 1 kg/L. Real water is slightly lighter than that, except near 4 °C.
| Liquid | kg/L | lb / US gal | lb / UK gal |
|---|---|---|---|
| Water (20 °C) Fresh water at room temperature | 0.998 | 8.33 | 10 |
| Seawater Average ocean salinity | 1.025 | 8.55 | 10.27 |
| Whole milk Varies slightly with fat content | 1.03 | 8.6 | 10.32 |
| Honey About 17–18% water | 1.42 | 11.85 | 14.23 |
| Maple syrup At standard 66–67 °Brix | 1.33 | 11.1 | 13.33 |
| Olive oil Other vegetable oils 0.91–0.93 | 0.915 | 7.64 | 9.17 |
| Gasoline (petrol) Typically 0.72–0.77 | 0.74 | 6.18 | 7.42 |
| Diesel Typically 0.82–0.86 | 0.85 | 7.09 | 8.52 |
| Jet A / Jet A-1 Planning figure 6.7 lb/US gal | 0.8 | 6.68 | 8.02 |
| Avgas 100LL Planning figure 6.0 lb/US gal | 0.72 | 6.01 | 7.22 |
| Propane (liquid) At 15.6 °C (60 °F) | 0.508 | 4.24 | 5.09 |
| Ethanol Pure, at 20 °C | 0.789 | 6.58 | 7.91 |
These are typical values. Fuels, oils and syrups vary by batch, grade and temperature, so for billing, shipping or load calculations use the density on the product's data sheet and choose "Other" in the converter.
Water is densest at about 4 °C (39 °F) and expands as it warms. That is why sources quote anything from 8.33 to 8.35 lb per US gallon. Hot water is about 4% lighter than cold:
| Water temperature | kg/L | lb / US gal | lb / UK gal |
|---|---|---|---|
| 4 °C (39 °F) | 0.99997 | 8.345 | 10.022 |
| 20 °C (68 °F) | 0.99821 | 8.33 | 10.004 |
| 38 °C (100 °F) | 0.99299 | 8.287 | 9.952 |
| 60 °C (140 °F) | 0.9832 | 8.205 | 9.854 |
| 100 °C (212 °F) | 0.95835 | 7.998 | 9.605 |
The imperial gallon was originally defined in 1824 as the volume of 10 lb of water, which is why a UK gallon of water still weighs almost exactly 10 lb.
A hot tub holds 400 US gallons, heated to 38 °C (100 °F). Before putting it on a deck, how much does the water weigh?
Step 1: Weight per gallon at 38 °C
Step 2: Multiply by the volume
The water alone is about 3,300 lb, roughly 1.5 tonnes. Add the empty tub and around 150–200 lb per person, and the total can pass 4,500 lb. Check this against the deck or slab rating. A 50-gallon water heater full of 60 °C water holds 410 lb of water for the same reason.
Pilots plan weight and balance with standard figures: 6 lb per US gallon for avgas and 6.7 lb per US gallon for Jet A. A light aircraft taking on 40 gallons of avgas is adding 240 lb. That can matter more than a passenger, so full tanks and full seats are not always possible together.
Fuel expands as it warms, so a gallon weighs a little less on a hot day while containing the same energy per pound. That is why aviation and shipping work in pounds or kilograms, and fuel pumps in gallons or litres. Propane is sold both ways: a standard "20 lb" barbecue cylinder holds 20 lb of propane, which is about 4.7 US gallons of liquid at 4.24 lb per gallon.
About 8.33 lb for a US gallon at room temperature (8.345 lb at 4 °C), and about 10.0 lb for a UK gallon.
About 12.0 US gallons (100 ÷ 8.33), or 10.0 UK gallons.
Choose "Other" and enter its density in kg/L or its specific gravity (the same number). Both are usually on the safety data sheet (SDS).
Slightly. Whole milk is about 3% denser, so a US gallon weighs around 8.6 lb against 8.33 lb for water.
Gasoline is a mix of light hydrocarbons with a density of about 0.74 kg/L, so a US gallon weighs only around 6.2 lb. That is also why it floats on water.
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