Fuel Efficiency Converter
Convert MPG, L/100km, and km/L
Enter any value to see all conversions:
Quick Facts
- •30 MPG ≈ 7.84 L/100km
- •235.215 ÷ MPG = L/100km
- •Average US car: ~25 MPG (9.4 L/100km)
MPG vs L/100km
The US uses miles per gallon (MPG) — higher is better. Most of the world uses liters per 100 km (L/100km) — lower is better. The conversion isn't linear: going from 10 to 20 MPG saves more fuel than going from 30 to 40 MPG. A car getting 30 MPG uses about 7.84 L/100km.
Understanding the fuel efficiency converter
Fuel economy is measured two opposite ways. Miles per gallon counts distance per unit of fuel, so higher is better, while litres per 100 kilometres counts fuel per unit of distance, so lower is better. They are inverses, which means you cannot average MPG figures the way you average speeds, and a jump from 15 to 20 MPG saves far more fuel than a jump from 40 to 50.
Worked examples
Converting 32 US MPG to L/100km
- 1The conversion constant is 235.215.
- 2L/100km = 235.215 ÷ MPG.
- 3235.215 ÷ 32 = 7.35.
32 US MPG is about 7.4 L/100km.
Why 15 to 20 MPG beats 40 to 50 MPG
- 1Over 10,000 miles at 15 MPG: 667 gallons. At 20 MPG: 500 gallons. Saving 167 gallons.
- 2Over 10,000 miles at 40 MPG: 250 gallons. At 50 MPG: 200 gallons. Saving 50 gallons.
- 3The smaller MPG improvement saves more than three times the fuel.
Upgrading an inefficient vehicle saves far more fuel than improving an already efficient one.
MPG to L/100km and km/L
| US MPG | UK MPG | L/100km | km/L |
|---|---|---|---|
| 15 | 18.0 | 15.7 | 6.4 |
| 20 | 24.0 | 11.8 | 8.5 |
| 25 | 30.0 | 9.4 | 10.6 |
| 30 | 36.0 | 7.8 | 12.8 |
| 35 | 42.0 | 6.7 | 14.9 |
| 40 | 48.0 | 5.9 | 17.0 |
| 50 | 60.0 | 4.7 | 21.3 |
| 60 | 72.1 | 3.9 | 25.5 |
A UK gallon is 4.546 litres against 3.785 for a US gallon, so UK MPG figures always look about 20 percent better.
Practical tips
- •Fill the tank, reset the trip meter, then fill again and divide miles by gallons added. That real-world figure beats the dashboard estimate.
- •Tyres 20 percent under pressure cost roughly 3 percent in fuel economy.
- •Highway speed matters more than most drivers expect. Economy typically falls about 10 percent going from 60 to 70 mph.
Frequently asked questions
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This calculator is for educational and reference purposes only. Always verify critical calculations independently.