Gas Mileage Calculator

Categories: Tools & Calculator

Calculate your vehicle’s actual gas mileage (MPG or L/100km) using trip distance or odometer readings. Easily convert between Imperial and Metric fuel economy.

Gas Mileage Calculator

Calculate using Odometer Readings
miles
Distance traveled on a single tank of fuel.
gal
The amount of fuel required to fill the tank back up.
Please check your inputs. Current odometer must be greater than previous odometer.

Calculated Fuel Economy

0.0 MPG
Liters per 100 Kilometers (L/100km): 0.00 L/100km
Kilometers per Liter (km/L): 0.00 km/L
MPG (UK / Imperial): 0.00 MPG

The Fuel Economy Formulas

Your vehicle's gas mileage represents its fuel efficiency, calculated by measuring the distance traveled over the amount of fuel consumed. This metric is represented as either a distance-per-fuel ratio (like MPG) or a fuel-per-distance ratio (like L/100km).

The standard equations used by this calculator are detailed below:

1. Imperial Calculation Method (Miles Per Gallon - US)

This is the standard measurement used in the United States, tracking the average miles traveled per single US gallon of fuel:

Miles Per Gallon (MPG) = Distance (Miles) ÷ Fuel Filled (Gallons)

To determine the United Kingdom (UK) Imperial MPG rating, multiply the US MPG result by 1.20095, as UK Imperial gallons are roughly 20% larger than US liquid gallons.

2. Metric Calculation Method (Liters per 100 Kilometers)

This system tracks the volume of fuel required to drive a fixed distance of 100 kilometers. This is the international standard throughout Europe, Canada, and Australia:

L/100km = [Fuel Filled (Liters) × 100] ÷ Distance (Kilometers)

3. Converting Between MPG and L/100km

To convert from one system to the other without starting from raw trip data, utilize the mathematical constant of 235.215:

L/100km = 235.215 ÷ MPG (US)MPG (US) = 235.215 ÷ L/100km

Fuel Economy Conversion Chart

The reference table below provides quick conversions between US MPG, Metric L/100km, and Kilometers per Liter (km/L) across common automotive economy classes.

MPG (US)MPG (UK / Imperial)Metric L/100kmMetric km/LRepresentative Vehicle Class
15.0 MPG18.0 MPG15.68 L/100km6.38 km/LHeavy-Duty Utility Trucks & V8 SUVs
20.0 MPG24.0 MPG11.76 L/100km8.50 km/LMidsize Crossovers & Older Sedans
25.0 MPG30.0 MPG9.41 L/100km10.63 km/LTypical Compact Sedans & Light SUVs
30.0 MPG36.0 MPG7.84 L/100km12.75 km/LModern Four-Cylinder Compacts
35.0 MPG42.0 MPG6.72 L/100km14.88 km/LSubcompact Cars & Mild Hybrids
40.0 MPG48.0 MPG5.88 L/100km17.01 km/LHigh-Efficiency Commuter Hybrids
50.0 MPG60.0 MPG4.70 L/100km21.26 km/LTop-Tier Dedicated Hybrids (e.g., Prius)

How to Manually Track Your True Gas Mileage

While modern dashboard trip computers estimate fuel efficiency, they often display slightly optimistic results. To find your vehicle's true, unvarnished gas mileage, adopt the manual paper-and-pen tank-fill method:

  1. First Fill-Up: Drive to the gas station and fill your tank until the pump nozzle clicks off automatically. Reset your trip odometer to zero, or note down your vehicle's current odometer reading (Odometer A).
  2. Drive Normally: Drive your vehicle as you typically would for commuting or trips until the tank is mostly empty.
  3. Second Fill-Up: Return to the pump. Fill the tank back up until the nozzle clicks off automatically. Note down two critical figures:
    • The exact number of gallons/liters needed to fill the tank (Fuel Filled).
    • Your trip odometer reading, or your vehicle's new odometer reading (Odometer B).
  4. Perform the Calculation:
    • If using odometer readings: Subtract Odometer A from Odometer B to find your total trip distance.
    • Divide your total trip distance by the amount of fuel filled during the second stop. This reveals your actual, real-world gas mileage.

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