Fuel Cost Calculator

The arithmetic in each unit system

Metric: fuel needed = distance ÷ 100 × L/100km, then cost = fuel × price per litre. The starting example, 300 km in a car that uses 7 L/100km with fuel at 1.85, needs 300 ÷ 100 × 7 = 21 L and costs 21 × 1.85 = 38.85.

Imperial: fuel needed = miles ÷ MPG, then cost = gallons × price per gallon. A 250-mile trip at 32 MPG with fuel at 3.60 needs 250 ÷ 32 = 7.8125 gallons, shown as 7.81 gal, and costs 28.13. The cost is calculated from the unrounded gallons, so it can differ by a cent from multiplying the displayed figure.

Converting between economy units

The imperial mode does not know which gallon you mean. It simply divides miles by MPG, so the MPG and the price must refer to the same gallon. US drivers can enter both as they appear at the pump. UK drivers usually know their MPG in imperial gallons but buy fuel per litre; the simplest fix is to switch to metric and convert MPG to L/100km with 282.48 ÷ MPG, so 40 MPG (UK) becomes 7.06 L/100km.

Rated economy versus real driving

Manufacturer figures come from standardised tests and are usually 10–20% better than what you see on the road. Motorway speeds above 110 km/h, cold starts, roof boxes, a full car, air conditioning and towing all raise consumption. The most reliable number to enter is the long-term average from your car's trip computer, or the figure you get by dividing litres filled by kilometres driven since the last full tank.

Return trips, car sharing and cost per kilometre

• The distance field is one-way unless you say otherwise: enter 600 km for a 300 km each-way trip.
• There is no passenger field. Divide the total cost yourself: 38.85 shared by three people is 12.95 each.
• Cost per kilometre is the total cost divided by the distance: 38.85 ÷ 300 = 0.13 per km, a handy figure for mileage claims or comparing with a train ticket.
• Set the distance to your weekly mileage to estimate a weekly fuel budget, or to annual mileage for the year.

What is and is not included

• Fuel only. Tolls, parking, wear and tear and depreciation are not part of the figure.
• The price is shown as a plain number without a currency symbol, so enter it in whatever currency you pay in.
• A 0 or empty value in any of the three fields hides the result.
• Fuel needed is rounded to two decimal places; the cost is rounded separately from the exact value.
• Electric cars work in metric mode if you ignore the labels: enter kWh per 100 km as the economy and the price per kWh as the price, and the result is the charging cost.