Fuel and water weight
Diesel: 0.84 kg/L typical at 15 °C (59 °F). The EN 590 diesel standard allows 0.82–0.845 kg/L (6.84–7.05 lb per US gallon).
A U.S. gallon of diesel weighs about 7.0 pounds (3.18 kg), a gallon of gasoline about 6.2 pounds (2.80 kg), fresh water about 8.34 pounds (3.78 kg) and seawater about 8.55 pounds (3.88 kg). The calculator multiplies the volume you enter by a typical density for each liquid, so you can add up full tanks before loading the boat or hitching the trailer.
Formula: weight = volume × density. With density in kilograms per liter, 1 U.S. gallon = 3.785 liters and 1 kilogram = 2.2046 pounds.
Weight of Diesel, Gasoline and Water per Gallon
| Liquid | Per U.S. gallon | Per liter |
|---|---|---|
| Gasoline | 6.18 lb (2.80 kg) | 0.740 kg (1.63 lb) |
| Diesel | 7.01 lb (3.18 kg) | 0.840 kg (1.85 lb) |
| Fresh water | 8.34 lb (3.78 kg) | 0.999 kg (2.20 lb) |
| Seawater | 8.55 lb (3.88 kg) | 1.025 kg (2.26 lb) |
An imperial gallon holds 4.546 liters, about 20% more than a U.S. gallon, so the same liquids weigh about 7.42 pounds (gasoline), 8.42 pounds (diesel), 10.01 pounds (fresh water) and 10.27 pounds (seawater) per imperial gallon. The imperial gallon was defined as the volume of 10 pounds of water, which is why an imperial gallon of water still weighs almost exactly 10 pounds.
The densities are typical values near 15 °C (59 °F): 0.74 kg per liter for gasoline, 0.84 for diesel, 0.999 for fresh water and 1.025 for seawater. Real fuel varies with the refinery, the season and the blend. Europe’s EN 228 gasoline standard allows 0.720 to 0.775 kg per liter and the EN 590 diesel standard 0.820 to 0.845; in EPA survey data, average U.S. gasoline comes out near 0.74 kg per liter in summer and 0.73 in winter. Seawater runs from about 1.02 to 1.03 kg per liter, depending on salt and temperature.
How Much Do 10 to 200 Gallons of Fuel Weigh?
| U.S. gallons | Diesel | Gasoline |
|---|---|---|
| 10 | 70.1 lb (31.8 kg) | 61.8 lb (28 kg) |
| 20 | 140 lb (63.6 kg) | 124 lb (56 kg) |
| 50 | 351 lb (159 kg) | 309 lb (140 kg) |
| 100 | 701 lb (318 kg) | 618 lb (280 kg) |
| 200 | 1,402 lb (636 kg) | 1,235 lb (560 kg) |
So 100 gallons of diesel weigh about 701 pounds, and a 200-gallon diesel load about 1,402 pounds. For a fuel amount that is not in the chart, enter it in the calculator above.
Water Weight per Gallon: Fresh Water and Seawater
| U.S. gallons | Fresh water | Seawater |
|---|---|---|
| 10 | 83.4 lb (37.8 kg) | 85.5 lb (38.8 kg) |
| 20 | 167 lb (75.6 kg) | 171 lb (77.6 kg) |
| 50 | 417 lb (189 kg) | 428 lb (194 kg) |
| 100 | 834 lb (378 kg) | 855 lb (388 kg) |
| 200 | 1,667 lb (756 kg) | 1,711 lb (776 kg) |
Seawater is about 2.6% heavier than fresh water because of the salt dissolved in it. A full 40-gallon fresh water tank holds about 333 pounds of water.
Why Fuel and Water Weight Matter on a Boat
- Load capacity. U.S. Coast Guard rules require a capacity plate on monohull boats under 20 feet, except sailboats, canoes, kayaks and inflatables. The plate shows the maximum persons capacity and the maximum weight the boat may carry. The Coast Guard’s method counts full built-in fuel tanks as part of the boat’s own weight, so fuel in portable tanks, water and gear count against the weight on the plate.
- Trailering. A trailer’s gross vehicle weight rating (GVWR) is its rated loaded weight, so the boat, motor, fuel, water and gear all count toward it. Filling a 100-gallon diesel tank adds about 701 pounds.
- Balance. Where the weight sits matters too. Boating safety courses advise spreading the load evenly and keeping it low, and moving weight changes how the boat trims.
How Temperature Changes Fuel Weight
Liquids expand as they warm, so a warm gallon holds a little less fuel by weight. Measurement Canada’s volume correction tables show that gasoline at 25 °C (77 °F) weighs about 1.3% less per gallon than at 15 °C (59 °F), and diesel about 0.85% less. Water changes even less: USGS figures give 0.99907 g/cm³ at 60 °F and 0.99669 g/cm³ at 80 °F, a difference of about 0.24%. The calculator uses the reference temperatures that fuel trade and fuel standards use, 15 °C or 60 °F, so expect small differences on very hot or very cold days.
Planning Fuel for a Trip
To estimate the fuel a trip needs from its distance, your cruising speed and your fuel burn, use the Boat Fuel Calculator, then enter that amount here to see what it weighs. The Boat Travel Time Calculator estimates the time underway for a route, and the 2 Stroke Oil Mix Calculator gives the oil to add to each tank of fuel for a two-stroke engine. To work out how much fuel a tank holds from its size, use the Boat Fuel Tank Calculator.
Frequently Asked Questions
How much does a gallon of diesel weigh?
About 7.0 pounds (3.18 kg) per U.S. gallon, using a typical diesel density of 0.84 kg per liter. Depending on the fuel, a gallon of diesel weighs roughly 6.8 to 7.1 pounds.
How much do 100 gallons of diesel weigh?
About 701 pounds, or 318 kilograms, for 100 U.S. gallons. For 100 imperial gallons it is about 842 pounds.
How much does a gallon of gasoline weigh?
About 6.2 pounds (2.80 kg) per U.S. gallon at 0.74 kg per liter. Europe’s EN 228 standard allows roughly 6.0 to 6.5 pounds per gallon, and winter gasoline is a little lighter than summer gasoline.
How much does a gallon of water weigh?
A U.S. gallon of fresh water weighs about 8.34 pounds (3.78 kg) at 60 °F. A gallon of seawater weighs about 8.55 pounds because of the salt dissolved in it.
How much does an imperial gallon of water weigh?
About 10 pounds (4.54 kg). The imperial gallon, 4.54609 liters or about 20% more than a U.S. gallon, was defined as the volume of 10 pounds of water.
Does fuel count toward my boat’s weight capacity?
On boats with a U.S. Coast Guard capacity plate, full built-in fuel tanks are already counted as part of the boat’s own weight. Fuel in portable tanks, water and gear count toward the maximum weight on the plate.