Fuel Consumption

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 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.

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.

History

Fuel economy measurement became critical during the 1973 Oil Crisis. The US Congress enacted CAFE (Corporate Average Fuel Economy) standards in 1975 to force automakers to improve efficiency. Metric countries naturally adopted L/100km (Liters per 100 kilometers) because it represents "fuel consumption" (how much fuel does it take to do a job), which scales linearly with cost. The US and UK stuck with MPG (Miles Per Gallon), which represents "fuel economy" (how far can I go on a unit). While intuitive for range ("I have 5 gallons, how far can I go?"), MPG can be misleading for savings. Improving from 10 to 20 MPG saves far more gas than improving from 40 to 50 MPG, a phenomenon known as the "MPG Illusion."