MPG Calculator
Your real gas mileage from a fill-up — plus conversions between MPG, L/100km, and km/L
Trip odometer since last fill
From the pump receipt
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Quick summary
The fill-up method is the accurate way to measure fuel economy: fill the tank, reset the trip odometer, drive normally, refill, then divide miles driven by gallons it took to refill. 350 miles on 12 gallons is 29.2 MPG. Convert mode translates between US MPG, UK MPG, L/100km (used in Europe/Canada — lower is better), and km/L.
Reviewed by Simple Calculators TeamLast reviewed
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Frequently asked questions
How do I calculate my car's real MPG?
Fill the tank completely, reset the trip odometer, drive normally for at least a few hundred miles, refill completely, and divide the miles by the gallons the refill took. Repeat over several tanks for the most reliable average — single tanks vary with conditions.
Why is my MPG lower than the sticker rating?
EPA figures come from standardized lab cycles. Cold weather, short trips, aggressive driving, roof loads, and city traffic all reduce real-world economy — 10–15% below sticker is normal, and winter city driving can be 20%+ below.
How do I convert MPG to L/100km?
235.215 ÷ MPG = L/100km, and the same formula converts back. 30 MPG ≈ 7.8 L/100km. Remember they run opposite directions — higher MPG is better, lower L/100km is better.
What's the difference between US and UK MPG?
The imperial (UK) gallon is 20% larger, so the same car scores 20% higher in UK MPG — 30 US MPG is 36 UK MPG. Always check which gallon a figure uses when comparing across countries.
Key terms
- Fill-Up Method
- Measuring economy between two complete fill-ups — the gold standard for real-world MPG.
- L/100km
- Liters per 100 kilometers — the metric standard where lower is better; 235.215 ÷ MPG.
- Imperial Gallon
- The UK gallon (4.546 L) — 20% larger than the US gallon (3.785 L).
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.