How Much Does a Gallon of Water Weigh? Gallons to Pounds Guide
By Elena Bennett · August 24, 2026
One US gallon of water weighs about 8.34 pounds. Use this quick guide to calculate the weight of 5, 10, 20, or more gallons before you lift, load, or build.
The short answer
1 US liquid gallon
8.34 lbs
5 US liquid gallons
41.70 lbs
This is water only. Add the weight of the jug, tank, aquarium, cooler, or other container to estimate the total load.
For everyday planning, a US gallon of water weighs approximately 8.34 pounds at room temperature. That number is the dependable baseline for estimating an RV freshwater payload, checking an aquarium stand, stocking emergency water, or deciding whether you can safely move a full container. The water itself is only part of the total: a five-gallon jug holds nearly 42 pounds of water before you add the weight of the jug, handle, pump, or shelf.
The simple gallons-to-pounds formula
Multiply the number of US liquid gallons by 8.34 to estimate the water weight in pounds. The result is accurate enough for ordinary household, camping, aquarium, and storage decisions.
Water weight in pounds = gallons × 8.34
Example: 20 gallons × 8.34 = 166.80 lbs of water
Gallons of water to pounds chart
Use these common conversions as a quick planning reference. All figures use a standard US liquid gallon and round to two decimal places.
| Water volume | Water weight | Real-world context |
|---|---|---|
| 1 gallon | 8.34 lbs | Standard milk-jug size |
| 5 gallons | 41.70 lbs | Office cooler jug or carboy |
| 10 gallons | 83.40 lbs | Small home aquarium |
| 20 gallons | 166.80 lbs | Medium aquarium or small RV tank |
US gallon versus UK Imperial gallon
This guide uses the US liquid gallon, which is the standard gallon measurement in the United States and equals about 8.34 pounds of water. A UK Imperial gallon is larger, so it holds more water and weighs about 10.02 pounds. If you are following an RV manual, aquarium specification, recipe, or equipment label from another country, confirm which gallon system it uses before calculating a load.
Does water temperature change the weight?
Yes, but usually not enough to change ordinary planning decisions. Water is slightly denser when cold and slightly less dense when hot. For lifting a jug, planning a shelf, or estimating vehicle payload, 8.34 pounds per US gallon is the accepted everyday number. Use a more precise density only for scientific, industrial, or engineering work where small differences matter.
Plan for the full load, not just the water
Water becomes heavy surprisingly fast, and large containers are often awkward rather than simply heavy. Build in a margin for the container and for movement, especially when the load will sit on furniture, a shelf, a vehicle, or a raised platform.
- A full 5-gallon container is nearly 42 pounds of water before the container itself. Use both hands, keep it close to your body, and avoid twisting while carrying it.
- For aquariums, add the tank, gravel, rocks, filter, and stand to the water weight. A filled aquarium can weigh much more than its nominal gallon rating suggests.
- For RVs and campers, include freshwater in your payload calculation. Every 10 gallons adds about 83 pounds before tanks, hoses, and gear.
Water weight at different temperatures
Temperature changes water density slightly. These approximate figures show why 8.34 pounds per US gallon is a practical everyday estimate.
| Condition | Approx. density | Weight per US gallon |
|---|---|---|
| Cold, 4°C / 39°F | 1.000 g/mL | 8.345 lbs |
| Room temperature, 20°C / 68°F | 0.998 g/mL | 8.330 lbs |
| Warm, 60°C / 140°F | 0.983 g/mL | 8.205 lbs |
How water compares with other liquids
Weight depends on density, so a gallon of another liquid may be lighter or heavier than water. Values below are useful approximations, not substitutes for a product specification.
| Liquid | Approx. pounds per US gallon |
|---|---|
| Fresh water | 8.34 lbs |
| Whole milk | 8.6 lbs |
| Vegetable oil | 7.7 lbs |
| Seawater | 8.55 lbs |
Gallons, liters, and kilograms
For metric planning, 1 US liquid gallon equals about 3.785 liters. Since 1 liter of water weighs close to 1 kilogram, a gallon of water weighs about 3.785 kilograms, or 8.34 pounds.
1 US gallon = 3.785 L ≈ 3.785 kg = 8.34 lbs
5 gallons ≈ 18.93 kg · 10 gallons ≈ 37.85 kg · 20 gallons ≈ 75.71 kg
Water weight FAQ
How much does 5 gallons of water weigh?
Five US gallons of water weigh about 41.70 pounds. A real 5-gallon jug or carboy will weigh more because you also need to include the empty container, cap, handle, and any attached pump or dispenser.
How much does 10 gallons of water weigh?
Ten US gallons of water weigh approximately 83.40 pounds. This is only the water weight, so a filled tank, container, or aquarium setup will have a higher total weight.
How much does 20 gallons of water weigh?
Twenty US gallons of water weigh approximately 166.80 pounds. For an aquarium, add the glass or acrylic tank, substrate, decorations, equipment, and stand before assessing the total load.
How many pounds are in 1 gallon of water?
One US liquid gallon of water weighs about 8.34 pounds at room temperature. This is the standard conversion used for common household, camping, and DIY calculations. One UK Imperial gallon of water weighs about 10.02 pounds because an Imperial gallon is larger.