Gas Mileage Calculator
Calculate MPG or L/100km from distance travelled and fuel used.
About Gas Mileage Calculator
MPG (miles per gallon) and L/100km are inversely related: L/100km = 235.214 ÷ MPG. The constant 235.214 comes from converting miles to kilometres and gallons to litres. Because of the inverse relationship, improving from 10 to 20 MPG saves twice as much fuel per mile as improving from 20 to 40 MPG.
Formulas
Miles per gallon
MPG = distance in miles ÷ fuel in US gallons
- d_mi
- Distance in miles
- V_gal
- Fuel consumed in US gallons
L/100km
L/100km = (litres ÷ km) × 100
- V_L
- Fuel in litres
- d_km
- Distance in kilometres
Conversion between MPG and L/100km
L/100km = 235.214 ÷ MPG
- 235.214
- Conversion constant = 100 × (km/mi) × (L/gal)
Worked example
With the default values below, Gas Mileage Calculator returns Miles per Gallon (MPG) of 30.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Unitsone of Imperial (miles, US gallons), Metric (km, litres)
- Imperial (miles, US gallons)
- Distance Travelledaccepts 0.1–100,000 mi / km
- 300 mi / km
- Fuel Usedaccepts 0.1–10,000 gal / L
- 10 gal / L
- Fuel Price (optional)accepts 0–100 $ per gal / L
- 3.5 $ per gal / L
Results
- Miles per Gallon (MPG)
- 30.00
- Litres per 100 km
- 7.84
- Total Fuel Cost
- $35.00
- Cost per Mile/km
- 0.1167 $
Step by step
- 1Miles per gallon= 30 MPG
- 2Equivalent in the other system= 7.84 L/100kmMPG and L/100km are inversely proportional via the constant 235.214.
- 3Cost per mi= $0.1167 per mi
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why are MPG and L/100km inversely related?
MPG measures how far you go per unit of fuel (higher is better), while L/100km measures how much fuel you use per unit of distance (lower is better). Mathematically, one is the reciprocal of the other, scaled by unit conversions. This is why gas mileage improvements are subject to diminishing returns measured in MPG.
How do I calculate my gas mileage on a road trip?
Fill your tank completely and note the odometer. Drive normally. When you next fill up, note the number of gallons (or litres) it takes to re-fill and the new odometer reading. Divide the miles driven by gallons used, or multiply (litres / km) by 100.
What is considered good fuel economy?
For passenger cars in the US, EPA considers 30+ MPG (≤7.8 L/100km) good for a non-hybrid. Hybrids typically achieve 50–70 MPG (4.7–3.4 L/100km). SUVs and trucks generally fall in the 15–25 MPG range.
Does this use US or Imperial gallons?
US gallons (3.785 L). UK Imperial gallons are larger (4.546 L), so UK MPG figures are always higher than US MPG for the same vehicle. The L/100km figure is unambiguous.