# MPG Calculator (Gas Mileage)

URL: https://speedycalculator.com/calculators/everyday-life/gas-mileage/
Last updated: 2026-10-25

> The MPG calculator finds your car's real fuel economy from the distance driven and the fuel used, in US and UK miles per gallon, km/L and L/100 km, plus the cost per mile and per trip.

## Inputs

- Distance driven (mi, km, m, nmi)
- Fuel used (US gal, L, UK gal)
- Fuel price (/US gal, /L, /UK gal)

## Results

- Fuel economy
- Fuel consumption
- Cost of the fuel
- Cost per distance

## Formula

```
MPG = distance ÷ fuel used
L/100 km = 100 × litres ÷ kilometres
Cost per mile = fuel price ÷ MPG
```

## Explanation

The most accurate way to measure fuel economy is the fill-to-fill method: fill the tank, reset the trip meter, drive normally, then fill up again and note the litres or gallons added. Dashboard figures are often 3–5% optimistic.

### How to use the MPG Calculator

- **Distance driven**
- **Fuel used**
- **Fuel price**
- Every result field is editable: type into **Fuel economy** and **Fuel used** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the distance since your last fill-up and the fuel you added, plus the fuel price. Type a target mpg into the result to see how much fuel that distance would take.

### Tips

- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field's menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.

### Common mistakes to avoid

- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.

### Inputs explained

FieldWhat to enterDistance drivenUnits: mi, km, m, nmiFuel usedUnits: US gal, L, UK galFuel priceUnits: /US gal, /L, /UK gal

### What each result means

- **Fuel economy** = [Distance driven]÷[Fuel used]
- **Fuel consumption** = 100000×[Fuel used]×1000÷[Distance driven]
- **Cost of the fuel** = [Fuel used]×[Fuel price]
- **Cost per distance** = [Fuel price]÷[Fuel economy]

### Example values

How the main result changes when **Fuel used** changes and everything else stays at the example values above:

Fuel used (US gal)Fuel economy (mpg (US))658.33938.891229.171523.331819.442414.58

## Worked example

Inputs — Distance driven: 350 mi; Fuel used: 12 US gal; Fuel price: $3.5 /US gal.

Results — **Fuel economy = 29.17 mpg (US)**; Fuel consumption = 8.06 L/100 km; Cost of the fuel = $42.00; Cost per distance = $0.120 /mi.

## FAQ

**How do I calculate MPG?**
Divide miles driven by gallons used: 350 miles ÷ 12 gallons = 29.2 mpg.

**What is the difference between US and UK mpg?**
A UK (imperial) gallon is 4.546 L versus 3.785 L, so UK mpg figures are about 20% higher for the same car.

**How do I convert mpg to L/100 km?**
235.21 ÷ US mpg (or 282.48 ÷ UK mpg).

**What formula does the MPG Calculator use?**
MPG = distance ÷ fuel used.