Fuel Efficiency Calculator
Convert fuel efficiency between MPG, L/100km, and km/L — includes trip fuel cost calculation for road trips and commutes.
Calcady™ · Calculation Report Fuel Efficiency Calculator calcady.com Trip MetricsUS Standard (MPG) 25.0Miles/Gal European Standard 9.4 L / 100km Kilometers Per Liter 10.6 KM / L |
Quick Answer: How Do You Convert MPG to L/100km?
Divide 235.215 by the MPG value. A car rated at 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. The conversion is inverse — higher MPG means lower L/100km. Note: US gallons (3.785L) and Imperial gallons (4.546L) are different — this calculator uses US gallons by default.
MPG ↔ L/100km Quick Reference
| MPG (US) | L/100km | km/L | Typical Vehicle |
|---|---|---|---|
| 15 MPG | 15.7 | 6.4 | Full-size truck (towing) |
| 25 MPG | 9.4 | 10.6 | Mid-size SUV |
| 35 MPG | 6.7 | 14.9 | Compact sedan |
| 50 MPG | 4.7 | 21.3 | Hybrid sedan |
| 130 MPGe | 1.8 | 55.3 | Full electric (MPGe equivalent) |
L/100km is used in Canada, Europe, and Australia. Lower is better (inverse of MPG where higher is better). US and Imperial gallons differ — 1 Imperial gallon = 1.2 US gallons.
Fuel Efficiency Tips
Do This
- ✓Use real-world MPG, not EPA window sticker. EPA ratings are based on lab testing. Real-world efficiency is typically 10-20% lower. Track your actual fill-ups over several tanks to get your true MPG for accurate trip cost calculations.
- ✓Remember that MPG improvements are non-linear. Going from 15 to 20 MPG saves more fuel per mile than going from 35 to 50 MPG. A truck improving from 15→20 MPG saves 1.67 gallons per 100 miles. A car improving from 35→50 MPG saves only 0.86 gallons per 100 miles.
Avoid This
- ✗Don't mix US and Imperial gallons. A UK car rated at "40 MPG" (Imperial) is actually 33.3 MPG (US). Imperial gallons are 20% larger. If you're comparing US and UK vehicle specs, convert to L/100km first — it's the universal standard.
- ✗Don't assume highway MPG for city driving. City efficiency can be 25-40% worse than highway due to stop-start driving, idling, and acceleration losses. Plan commute costs using your city rating, not the combined or highway number.
Frequently Asked Questions
Why is L/100km used instead of km/L?
L/100km measures fuel consumption (how much fuel for a fixed distance), which scales linearly — 10 L/100km uses exactly twice as much fuel as 5 L/100km. MPG and km/L measure fuel economy (how far on a fixed amount of fuel) which is non-linear. This makes L/100km better for comparing savings: dropping from 10 to 8 L/100km saves the same amount as dropping from 6 to 4.8 L/100km.
What is MPGe for electric vehicles?
MPGe (Miles Per Gallon equivalent) measures how far an electric vehicle travels on the energy equivalent of one gallon of gasoline (33.7 kWh). A Tesla Model 3 at 130 MPGe means it travels 130 miles on 33.7 kWh of electricity. To calculate actual cost, use your electricity rate instead: 33.7 kWh × $0.13/kWh = $4.38 per "gallon equivalent" vs $3.50 for actual gasoline — but the EV travels 4× further on that energy.
How do I calculate trip fuel cost?
Divide trip distance by your MPG, then multiply by fuel price. A 500-mile trip in a 25 MPG car at $3.50/gallon: 500 ÷ 25 = 20 gallons × $3.50 = $70.00 in fuel. For round trips, double it. Add 10-15% for city driving segments, detours, and AC use — a 500-mile highway trip with city stops and AC will use closer to 22 gallons.