Convert fuel and water gallons to pounds using common densities: gasoline ~6.1 lb/gal, diesel ~7.1, freshwater ~8.34. Add rows for multiple tanks.
Enter tank 1 gallons, tank 2 gallons, and tank 3 gallons.
Convert fuel and water gallons to pounds using common densities: gasoline ~6.
Each row multiplies gallons by the selected density. Densities are common planning figures; temperature and blend shift real weight slightly.
lb = gallons × density_lb_per_gal
gasoline 6.1 · diesel 7.1 · freshwater 8.34
total = sum of rows
Useful for trailer tongue, float-plane, or displacement planning — not a substitute for a scale.
Start with the calculator’s default entries: Tank 1 type = Gasoline (6.1 lb/gal); Tank 1 gallons = 50; Tank 2 type = Diesel (7.1 lb/gal); Tank 2 gallons = 0; Tank 3 / water = Freshwater (8.34 lb/gal); Tank 3 gallons = 20.
With those entries the calculator returns:
472 lb total
2 tank row(s) summed
T1: 50 × 6.1 = 305.0 lb
T3: 20 × 8.34 = 166.8 lb
total = 471.8 lb
Formula used: lb = gallons × density_lb_per_gal gasoline 6.1 · diesel 7.1 · freshwater 8.34 total = sum of rows
One input at a time. Raise Tank 1 gallons from 50 to 75 and leave everything else alone. The result becomes:
624 lb total
T1: 75 × 6.1 = 457.5 lb
total = 624.3 lb
This boat fuel weight page models the arithmetic shown in the formula box only.
Widely used planning densities for gasoline and diesel. Your fuel may differ a few tenths of a pound per gallon.
Set gallons to 0 for empty. Tank structure weight is not included.
Approximate with freshwater density if needed, or weigh when full if critical.