Fuel Economy Calculator

Fuel economy measures how efficiently a vehicle converts fuel into distance traveled. There are two common metrics: MPG (miles per gallon, used in the US) and L/100km (liters per 100 kilometers, used in most of the world). This page works from a single fill-up: the distance you covered, and the fuel it took to put the tank back to full.

MPG formula: MPG = Miles Driven ÷ Gallons Used

L/100km formula: L/100km = (Liters Used ÷ Kilometers Driven) × 100

Converting between the two: L/100km = 235.21 ÷ MPG

Cost of this fill-up (optional): Trip Cost = Fuel Used × Price per Unit Cost per Mile = Trip Cost ÷ Distance

Where:

• Distance Driven — the odometer at this fill-up minus the odometer at the last one, or the trip meter if you reset it when you filled
• Fuel Used — what it took to bring the tank back to full, straight off the pump receipt
• Price — leave it blank if you only want the economy figure. Enter it per gallon if you entered gallons, per liter if you entered liters.

US gallon or Imperial gallon? The US setting on this page uses US gallons of 3.785 L. The Imperial gallon still quoted in the UK is 4.546 L, roughly 20% larger, which is why British MPG figures always read flatteringly next to American ones for the same car. A car rated 30 MPG in the US is 36 MPG in Britain, with nothing changed but the size of the container. If your figures came off a UK forum, convert before comparing.

Fuel economy benchmarks:

• Economy cars (Civic, Corolla): 32–40 MPG combined
• Midsize sedans: 28–35 MPG
• SUVs and crossovers: 22–30 MPG
• Full-size trucks: 16–22 MPG
• Hybrid vehicles: 45–60 MPG
• Electric vehicles: equivalent 90–130 MPGe

Worked example: You reset the trip meter at the last fill-up. It now reads 320 miles, and the pump took 12.5 gallons at $3.80.

MPG = 320 ÷ 12.5 = 25.6 MPG As L/100km: 235.21 ÷ 25.6 = 9.19 L/100km (10.88 km/L) Trip cost = 12.5 × $3.80 = $47.50 Cost per mile = $47.50 ÷ 320 = 14.8 cents

Fill the tank the same way every time or the number is noise. The measurement depends entirely on both fill-ups stopping at the same level, and the pump’s auto-shutoff varies by a good half gallon between stations, and even between the fast and slow trigger settings on the same pump. On a 12-gallon fill, half a gallon of inconsistency is 4% of your answer. Click off at the first shutoff and do not top up to the neck. Then average three or four consecutive tanks before you believe any trend, because one tank tells you about that tank, not about the car.