Fuel Consumption
Convert between MPG (US & UK), Liters per 100km, and km/Liter. Compare fuel efficiency globally and understand the MPG illusion.
Formula
235.215 / MPG (US) = L/100km
Inverse relationship: As MPG goes up, L/100km goes down. The constant 235.215 accounts for gallon-liter and mile-km conversions.
Worked Examples
Example 1: US Sedan Rated in MPG, Shopping in Europe
Problem:A US-market sedan is rated 28 MPG (US) combined. What is that in L/100km, UK MPG, and km/L?
Solution:L/100km = 235.215 / 28 = 8.40. UK MPG = 28 x 1.20095 = 33.6. km/L = 28 / 2.35215 = 11.9.
Result:8.4 L/100km (33.6 MPG UK, 11.9 km/L)
Example 2: European Diesel Hatchback Quoted in L/100km
Problem:A rental listing in Germany advertises 5.5 L/100km. How efficient is that on a US window sticker?
Solution:US MPG = 235.215 / 5.5 = 42.8. UK MPG = 42.8 x 1.20095 = 51.4. km/L = 100 / 5.5 = 18.2.
Result:42.8 MPG (US), 51.4 MPG (UK), 18.2 km/L
Frequently Asked Questions
Why are US and UK MPG different?
The UK gallon (4.546L) is 20% larger than the US gallon (3.785L). Therefore, a car will always have a higher MPG figure in UK gallons than US gallons for the same efficiency.
What is L/100km?
Liters per 100 kilometers is the standard metric fuel economy measure. Unlike MPG, lower numbers are better (you use less fuel).
How to convert L/100km to MPG manually?
Divide 235.215 by the L/100km value to get US MPG. For example, 10 L/100km = 235.215 / 10 = 23.5 MPG.
Why is L/100km considered an "inverse" metric?
In MPG, higher is better (distance per unit). In L/100km, lower is better (consumption per distance). It measures "thirst" rather than "range".
What is a good fuel economy score?
Generally, >30 MPG (US) or <8 L/100km is considered good for a non-hybrid sedan. Hybrids often exceed 50 MPG (<4.7 L/100km).
Does driving speed affect fuel consumption?
Yes drastically. Aerodynamic drag increases with the square of speed. Driving at 80mph can consume 25% more fuel than driving at 65mph.
How to calculate fuel cost per mile?
Divide the price of fuel per gallon by your MPG. Example: $3.50/gal ÷ 25 MPG = $0.14 per mile.
What is km/L used in?
Kilometers per Liter is used in countries like Japan, Brazil, and India. It behaves like MPG (higher is better). 10 km/L ≈ 23.5 MPG (US).
How to improve fuel efficiency?
Check tire pressure, remove excess weight, avoid rapid acceleration, use cruise control on highways, and perform regular maintenance (air filters, oil).
Difference between city and highway MPG?
City driving involves stop-and-go traffic which wastes fuel (lower MPG). Highway driving is consistent and allows higher gears (higher MPG), though very high speeds reduce efficiency again.
Background & Theory
Conversion Formulas:
US MPG to L/100km:
$$L/100km = \\frac{235.215}{\\text{US MPG}}$$
UK MPG to L/100km:
$$L/100km = \\frac{282.48}{\\text{UK MPG}}$$
L/100km to US MPG:
$$\\text{US MPG} = \\frac{235.215}{L/100km}$$
km/L to US MPG:
$$\\text{US MPG} = \\text{km/L} \\times 2.352$$
The MPG Illusion:
The relationship between MPG and fuel consumption is non-linear.
- Switching from a 15 MPG truck to a 20 MPG crossover saves 16.7 gallons over 1000 miles.
- Switching from a 35 MPG sedan to a 40 MPG hybrid saves only 3.6 gallons over 1000 miles.
The low-end improvements are much more impactful for the environment and your wallet.