How road trip calculator Works
The formula
Fuel cost = total miles ÷ MPG × price per gallon. The calculator doubles for round trips and divides by passengers for a fair split. A 480-mile leg at 30 MPG and $3.45: 960 miles round trip ÷ 30 × 3.45 ≈ $110, or $27.67 each with four people splitting — before the snack budget, which history suggests will rival it.
Use your real MPG, not the sticker
Highway cruising is where cars beat their EPA combined rating, but roof boxes, full loads, and 80-mph cruising eat it back. If you've run the MPG calculator on a recent tank, use that number — it's the honest one. Otherwise, use EPA highway and expect reality within ±10%.
The fuel-up plan
Knowing tank range (MPG × usable gallons — plan on ~90% of tank size) turns fuel stops from anxiety into schedule. At 30 MPG and a 14-gallon tank, realistic range is ~380 miles — so a 960-mile round trip is 3 planned stops, not 5 prayers. Rural West Texas and Nevada reward exactly this math.
What this doesn't cover
Fuel is typically 60–70% of a road trip's marginal cost. Tolls, one night's lodging, oil-change timing if you're crossing service intervals, and tire wear all ride along. Budget fuel with the calculator; budget the rest with your itinerary.