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MPG Calculator

AutomotiveFuel Economy and Running Costs
Units

Optional. Price per gallon (US) or per litre (metric), in your currency.

Fuel economy (US MPG) —
Litres per 100 km
—
Kilometres per litre
—
UK MPG (imperial gallon)
—
Fuel cost for this distance
—
Fuel cost per mile or km
—

MPG is the distance you drove divided by the fuel it took to refill the tank. Drive 300 miles, refill with 10 US gallons, and the car returned 30 MPG, which equals about 7.84 litres per 100 km or 36.03 MPG measured in UK imperial gallons. Add the fuel price to see the cost per mile.

About this tool

Drivers checking a car's real consumption against its window sticker, fleet managers logging fill-ups, and anyone comparing a US review with a European one all need the same sum: distance over fuel. Enter the trip odometer reading and the amount you put in at the pump, in miles and US gallons or in kilometres and litres. The calculator returns US MPG as the headline figure, plus litres per 100 km, kilometres per litre and UK MPG, since the imperial gallon is about 20% larger and makes the same car look thriftier. An optional fuel price adds the cost of the distance and the cost per mile or kilometre. One fill-up is a noisy sample: pump shut-off points vary, so average several tanks before drawing conclusions about a car or a driving habit.

How to use it

  1. Pick your units

    Choose miles and US gallons or kilometres and litres; the distance and fuel fields switch to match.

  2. Enter distance and fuel

    Use the trip meter reading since the last full tank and the volume needed to fill it again.

  3. Add a price if you want costs

    Type the price per gallon or per litre to get the cost of the distance and the cost per mile or km.

  4. Read the conversions

    Compare US MPG with L/100 km, km per litre and UK MPG, and follow the working shown below them.

Examples

300 miles on a 10-gallon fill

Units
Miles and US gallons
Distance driven
300
Fuel used to refill
10

Result Fuel economy (US MPG): 30
Litres per 100 km: 7.84
Kilometres per litre: 12.75
UK MPG (imperial gallon): 36.03
Fuel cost for this distance: —
Fuel cost per mile or km: —

  1. Distance = 300 mi = 482.8 km; fuel = 10 US gal = 37.85 L
  2. MPG (US) = miles ÷ US gallons = 30
  3. L/100 km = litres ÷ km × 100 = 7.84
  4. MPG (UK) = MPG (US) × 4.54609 ÷ 3.785411784 = 36.03

A typical highway tank: 30 US MPG works out to about 7.8 litres per 100 km and 36 MPG on the UK imperial gallon.

500 km on 40 litres

Units
Kilometres and litres
Distance driven
500
Fuel used to refill
40

Result Fuel economy (US MPG): 29.4
Litres per 100 km: 8
Kilometres per litre: 12.5
UK MPG (imperial gallon): 35.31
Fuel cost for this distance: —
Fuel cost per mile or km: —

  1. Distance = 500 km = 310.69 mi; fuel = 40 L = 10.567 US gal
  2. MPG (US) = miles ÷ US gallons = 29.4
  3. L/100 km = litres ÷ km × 100 = 8
  4. MPG (UK) = MPG (US) × 4.54609 ÷ 3.785411784 = 35.31

A European odometer reading: 8 L/100 km is the same car as 29.4 US MPG.

300 miles at 3.50 per gallon

Units
Miles and US gallons
Distance driven
300
Fuel used to refill
10
Fuel price per unit
3.5

Result Fuel economy (US MPG): 30
Litres per 100 km: 7.84
Kilometres per litre: 12.75
UK MPG (imperial gallon): 36.03
Fuel cost for this distance: 35.00
Fuel cost per mile or km: 0.117

  1. Distance = 300 mi = 482.8 km; fuel = 10 US gal = 37.85 L
  2. MPG (US) = miles ÷ US gallons = 30
  3. L/100 km = litres ÷ km × 100 = 7.84
  4. MPG (UK) = MPG (US) × 4.54609 ÷ 3.785411784 = 36.03
  5. Fuel cost = 10 × 3.5 = 35; per mile = 0.117

Ten gallons at 3.50 cost 35.00, or just under 12 cents a mile.

How it is calculated

MPG = miles ÷ US gallons; L/100 km = litres ÷ km × 100 = 235.215 ÷ MPG; UK MPG = MPG × 4.54609 ÷ 3.785411784

miles
distance driven since the tank was last filled
US gallons
fuel needed to refill, 1 US gal = 3.785411784 L
4.54609
litres in one imperial (UK) gallon
1.609344
kilometres in one mile

Metric inputs are first turned into miles and US gallons using the exact legal definitions, so every figure comes from the same ratio. MPG and km per litre rise as economy improves, while L/100 km falls, which is why the two scales are reciprocal: halving consumption in L/100 km doubles MPG. The cost lines simply multiply the fuel used by the price you entered and divide by the distance.

When not to use it

  • Electric cars use kWh per mile or MPGe, not litres or gallons.
  • Plug-in hybrids that charged during the trip will show an inflated figure.
  • A partial refill does not tell you how much fuel the trip actually burned.

Common mistakes

  • Mixing UK MPG from a British review with US MPG from the EPA label.
  • Using the tank size instead of the amount needed to refill it.
  • Judging a car on one tank instead of the average of several fills.
  • Forgetting to reset the trip meter at the previous fill-up.

Frequently asked questions

Why is UK MPG higher than US MPG for the same car?

An imperial gallon holds 4.54609 litres and a US gallon 3.785411784 litres, so the UK gallon is about 20% bigger. The same car covers more miles on the larger gallon: 30 US MPG equals about 36 UK MPG.

How do I convert MPG to litres per 100 km?

Divide 235.215 by the US MPG figure. 30 MPG becomes 7.84 L/100 km and 40 MPG becomes 5.88 L/100 km. For UK MPG use 282.481 instead of 235.215.

What is the most reliable way to measure my MPG?

Fill the tank until the pump clicks off, reset the trip meter, drive normally, then refill at the same pump the same way. Divide the miles by the gallons added. Repeat over three or four tanks and average them to smooth out shut-off differences.

Why does my measured MPG differ from the window sticker?

Official ratings come from standard lab test cycles. Real figures move with speed, cold weather, short trips, tyre pressure, roof loads and air conditioning. Winter driving and lots of short journeys commonly cut economy by 10 to 20 percent.

Does the price field need a currency?

No. Enter the price per gallon or per litre in whatever currency you pay in, and the cost of the distance and cost per mile or kilometre come out in that same currency.

Is km per litre the same as L/100 km?

They are reciprocals. 12.5 km per litre means 100 km takes 8 litres. Higher km per litre is better, while lower L/100 km is better.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 21). MPG Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/automotive/fuel-economy-and-running-costs/mpg-calculator/

MLA

Tools Directory Editorial Team. “MPG Calculator.” Tools Directory, 21 Oct. 2026, https://tools.milunir.com/automotive/fuel-economy-and-running-costs/mpg-calculator/. Accessed 26 Oct. 2026.

Chicago

Tools Directory Editorial Team. “MPG Calculator.” Tools Directory. Last modified October 21, 2026. Accessed October 26, 2026. https://tools.milunir.com/automotive/fuel-economy-and-running-costs/mpg-calculator/.

Link<a href="https://tools.milunir.com/automotive/fuel-economy-and-running-costs/mpg-calculator/">MPG Calculator – Tools Directory</a>