How the fuel cost is calculated
The tool multiplies the distance by two if you select round trip, then works out how much fuel you'll burn. In imperial mode it divides the distance by your miles-per-gallon to get gallons used; in metric mode it multiplies distance by your liters-per-100km figure and divides by 100 to get liters. It multiplies the fuel used by the price you entered, adds any tolls and parking, and divides the total by the number of passengers to give each person's share.
Choosing the right units
Fuel economy is expressed two opposite ways around the world. MPG (miles per gallon) means higher is better — more distance per unit of fuel. L/100km (liters per 100 kilometers) means lower is better — less fuel per fixed distance. The calculator handles either; just make sure your fuel economy, distance, and price all use the same system, since mixing miles with liters produces nonsense. The unit toggle relabels every field to keep them consistent.
What the estimate leaves out
This is a fuel-cost estimate, not the full cost of driving. It excludes depreciation, maintenance, tires, and insurance, which together often cost as much as fuel or more. For the true economic cost — for example when deciding whether to drive or claim mileage — a per-mile rate like the IRS standard mileage rate captures those hidden costs far better. Real-world fuel economy also drops with high speed, heavy loads, cold weather, and lots of stop-and-go driving, so pad the estimate for tough conditions.
A worked example
A 300-mile one-way drive in a car doing 30 MPG, with fuel at $3.50 a gallon and two people aboard, uses 10 gallons and costs $35.00, or $17.50 each. Switch on round trip and it doubles to 20 gallons and $70.00 total, $35.00 per person. Add $12 in tolls and $8 parking and the total becomes $90.00, or $45.00 each — a clear, fair split for a shared journey.
Tips for splitting fairly
Include the driver in the passenger count so the cost is shared evenly, or exclude them if the group agrees the driver's contribution is the car and their time. For commuting or business travel, keep a note of the mileage — it may be tax-deductible at your local standard rate, which is usually far more generous than fuel alone. For long trips, check current local fuel prices rather than a national average for the most accurate figure.