Calculators / Fuel and water weight
Fuel and water weight
What does all that water weigh, and what does slowing down save?
Tank water is heavy. Speed is thirsty. Here is the weight in pounds, and an optional estimate of the gallons you keep by easing off.
How the math works
- Water weight =
gallons × 8.34 lb. - The class weights and drag notes are copied from the old Megawatt widget. Its script was cut off in the fifth wheel branch, before any gallon math, so the fifth wheel weight starts blank and the original fuel formula is not shown as if it were known.
- The speed estimate is opt in and clearly labeled: on the highway, fuel over a fixed distance roughly follows speed squared, because drag does. So
gallons saved = trip gallons × (1 − new speed² ÷ old speed²). - Trip gallons are your miles divided by your MPG. No MPG, no gallons.
Same formula and constants as the calculator on the previous megawattrv.com. This is a planning tool. Have a qualified electrician check anything you wire.