Road Trip Cost Calculator
Fuel used and total cost for any drive from distance and mileage.
What it does
A road trip budget is distance divided by economy times price. The car drinks a fixed amount per mile on average, and the pump multiplies those gallons by the local price, so three numbers set the whole fuel budget.
The tool above runs both unit systems. Imperial takes miles, miles per gallon, and dollars per gallon, while metric takes kilometers, liters per 100 km, and price per liter. Both return fuel used, total cost, and cost per distance.
The default example drives 300 miles at 30 mpg with $3.50 gas: 10 gallons for $35.00, about $0.12 a mile. The metric mirror of 482.8 km at 7.84 L/100km and $0.92 per liter burns 37.85 L for $34.82, the same trip through converted units.
Economy figures come from EPA ratings published on fueleconomy.gov with EIA price outlooks as the second leg. Real trips vary with speed, hills, roof boxes, and cold starts, so logged personal mpg beats the sticker for repeat routes.
How to use
- Pick imperial for miles and gallons or metric for km and liters.
- Enter the one way or round trip distance in that system.
- Enter your real economy: mpg or L/100km from past fill ups.
- Enter the fuel price per gallon or per liter.
- Read fuel used first, then total cost and cost per mile or km.
Formula
- mpg
- Miles per US gallon at your driving style.
- L/100km
- Liters burned per 100 km, lower is better.
- price
- Pump price per gallon or per liter.
Convert between the two economies with 235.214583 / mpg = L/100km. Zero price is allowed and returns fuel used with zero cost for planning without local prices.
Worked example
Example: 300 miles at 30 mpg, $3.50 a gallon
Imperial defaults: 300 mi, 30 mpg, $3.50 per gallon.
- Gallons: 300 / 30 = 10 gal.
- Liters check: 10 x 3.78541 = 37.85 L.
- Cost: 10 x 3.50 = $35.00.
- Per mile: 35 / 300 = $0.12 /mi. Economy is 235.214583 / 30 = 7.84 L/100km.
- Tool shows 10 gal, $35.00, $0.12 /mi.
Reference table
| Economy | Fuel | Cost |
|---|---|---|
| 20 mpg | 15 gal | $52.50 |
| 30 mpg | 10 gal | $35.00 |
| 40 mpg | 7.5 gal | $26.25 |
Limits
- Fuel only. Tolls, food, stays, and wear sit outside.
- Steady economy assumed. City legs and mountains drink more.
- One price for the whole route; borders and highways vary.
- Round trips need double distance entered.
Common mistakes
- Using sticker mpg for a loaded roof box trip at speed.
- Mixing UK gallons with US gallons (20% larger).
- Forgetting the return leg on distance.
- Pricing premium when the car takes regular, or reverse.
- Ignoring that cold starts add liters the rating never sees.
Try it yourself
Quick checks. Answers sit tucked under each question.
200 miles at 25 mpg, $4 a gallon?
8 gal for $32.00, about $0.16 a mile.
482.8 km at 7.84 L/100km, $0.92 per liter?
37.85 L for $34.82, about $0.07 per km.
Cost per mile at $35 over 300 miles?
35 / 300 = $0.12 per mile.
Questions
How do you calculate trip fuel cost?
Distance divided by economy times price: 300 / 30 x 3.50 = $35.00.
mpg to L/100km?
Divide 235.214583 by mpg. 30 mpg is 7.84 L/100km.
Where do economy numbers come from?
EPA ratings on fueleconomy.gov plus your own fill up logs, which run truer for your car.
Does speed matter?
Yes. Drag grows fast past highway pace, so 80 mph can drink 20% more than 65 mph.
What is missing from the total?
Tolls, parking, food, lodging, and maintenance. This page prices fuel alone.
How do I split costs fairly?
Divide the fuel total by riders, then add shared tolls and parking on top.