MPG & Fuel Economy Calculator

Calculate Fuel Economy

km
L

Fuel Economy

7.5 L/100km

Equivalent

31.4

MPG (equivalent)

See how this is calculated

How This Calculation Works

This calculator finds your vehicle's real fuel economy from a simple fill-up-to-fill-up measurement: distance driven divided by fuel consumed. In imperial units, this gives miles per gallon (MPG) directly. In metric units, it gives liters per 100 kilometers (L/100km) — the standard metric fuel economy measure, calculated as (fuel used ÷ distance) × 100.

Unlike MPG, where a higher number is better, L/100km works in reverse — a lower number means better fuel economy, since it represents how much fuel is consumed over a fixed distance. The calculator also converts between the two systems so you can compare a metric-rated vehicle against an imperial-rated one, or vice versa.

The conversion factor between the two systems is roughly 235.215 — dividing this number by your L/100km figure gives an approximate MPG equivalent, and dividing it by your MPG gives an approximate L/100km equivalent. This constant comes from converting the different distance and volume units embedded in each measurement system.

Common Mistakes to Avoid

  • Not filling the tank completely for measurements. For an accurate reading, always fill the tank completely both at the start and end of your measurement period — partial fills introduce significant error into the calculation.
  • Using a single tank as a permanent average. Fuel economy varies by season, driving conditions, and trip type. Average several fill-ups over weeks or months for a more representative long-term figure.
  • Confusing MPG and L/100km direction. Remember that for MPG, higher is better (more distance per unit of fuel), while for L/100km, lower is better (less fuel per unit of distance) — mixing these up is a common source of confusion when comparing vehicles across regions.
  • Forgetting US vs. UK/Imperial gallon differences. A US gallon (3.785 L) is smaller than a UK/Imperial gallon (4.546 L), so MPG figures from US and UK sources aren't directly comparable without conversion.

Worked Example

Scenario: A driver fills up, drives 500 km, then refills using 37.5 liters.

Step 1 — L/100km: (37.5 ÷ 500) × 100 = 7.5 L/100km.

Step 2 — MPG equivalent: 235.215 ÷ 7.5 ≈ 31.4 MPG.

This vehicle uses 7.5 liters of fuel for every 100 km driven, equivalent to roughly 31.4 miles per gallon.

Frequently Asked Questions

What's a good fuel economy figure?
It varies widely by vehicle type. Small, efficient gasoline cars often achieve 35-45 MPG (5.2-6.7 L/100km), midsize sedans typically get 25-35 MPG (6.7-9.4 L/100km), and larger SUVs or trucks often fall in the 15-25 MPG (9.4-15.7 L/100km) range. Hybrid and electric vehicles can exceed these figures significantly.
How often should I recalculate my fuel economy?
Checking every fill-up gives you the most data, but averaging over 3-5 fill-ups smooths out short-term variation from weather, traffic, or short trips versus highway driving, giving a more representative long-term figure for budgeting purposes.
Why does my actual MPG differ from the sticker rating?
EPA and similar official ratings are measured under controlled, standardized test conditions that don't fully replicate real-world driving. Aggressive acceleration, cold weather, air conditioning, traffic, and terrain all typically reduce real-world fuel economy below the official rating.
Is L/100km or MPG more precise for comparing efficient cars?
L/100km is actually considered more intuitively precise for comparing fuel savings, because it scales linearly with fuel consumption. In MPG, the difference between 40 and 50 MPG in real fuel savings is much smaller than the same numeric gap between 10 and 20 MPG — a quirk of the inverse relationship that L/100km avoids.

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