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MPG Calculator | Compute Fuel Economy In MPG, L/100km, And km/L

Calculates your vehicle's real fuel economy. Enter the miles driven and the gallons of fuel used, and the tool returns MPG, litres per 100 km, and kilometres per litre, with a note on how your driving style and conditions affect the result.

Last updated: June 2026 · Free · No sign-up required

miles
gallons
$
Results

Enter values above and click Calculate to see your result instantly.

Quick reference

You droveFuel usedMPG
300 miles15 gal20.0
350 miles12.5 gal28.0
400 miles11 gal36.4
450 miles9 gal50.0

info MPG Calculator

Free everyday calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

MPG (combined)Meaning
Under 20Below average — typical for trucks, large SUVs, towing
20–29Average for most gas cars and crossovers
30–39Efficient — compact cars, modern sedans
40+Excellent — hybrids and the most efficient models

lightbulb Worked example

Let's say you are using the MPG Calculator. Calculates your vehicle's real fuel economy. Enter the miles driven and the gallons of fuel used, and the tool returns MPG, litres per 100 km, and kilometres per litre, with a note on how your Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula MPG = miles driven ÷ gallons of fuel used; L/100km = 235.215 ÷ MPG and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: MPG = miles driven ÷ gallons of fuel used; L/100km = 235.215 ÷ MPG

The MPG Calculator is built on a well-established calculation method. It uses the formula MPG = miles driven ÷ gallons of fuel used; L/100km = 235.215 ÷ MPG to turn your inputs into a reliable result. Calculates your vehicle's real fuel economy. Enter the miles driven and the gallons of fuel used, and the tool returns MPG, litres per 100 km, and kilometres per litre, with a note on how your driving style and The steps are shown on the page so you can follow the reasoning from input to output.

  1. Fill your tank completely and reset the trip odometer (or note the mileage).
  2. Drive normally until the next fill-up.
  3. Refill the tank and note the gallons it took and the trip miles.
  4. Divide miles by gallons — that quotient is your real-world MPG.

Worked example: 350 miles on 12.5 gallons → 350 ÷ 12.5 = 28.0 MPG (8.40 L/100km). At $3.50/gal that's $0.125 per mile.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate my MPG?
Enter the required values into the input fields and press the calculate button. The tool applies the formula MPG = miles driven ÷ gallons of fuel used; L/100km = 235.215 ÷ MPG and returns the result with a short explanation of each step, so you can check the working yourself.
How do I figure out miles per gallon without a full tank?
Fill the tank completely and reset the trip odometer, drive until you need fuel, then fill again and note the gallons pumped. MPG = miles driven ÷ gallons used. You do not need to drain the tank — the second full fill measures exactly what you consumed. The calculator also works in km/L and L/100km.
What is a good MPG?
The MPG Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Calculates your vehicle's real fuel economy. Enter the miles driven and the gallons of fuel used, and the tool returns MPG, litres per 100 km, and kilometres per litre, with a note on how your driving style and conditions affect the result. There is no limit on usage, and it works on any device.
How do I convert MPG to liters per 100 km?
Use the reciprocal conversion L/100km = 235.215 ÷ MPG. A vehicle getting 30 MPG uses about 7.84 L/100km, and 40 MPG about 5.88 L/100km. The factor combines the mile-to-km and gallon-to-liter conversions. The calculator returns both measures from your miles-and-gallons input, so you can quote either standard.
Why is my calculated MPG lower than the window sticker?
The sticker figure comes from controlled lab tests with optimal conditions, while real driving includes city traffic, cold starts, hills, air conditioning, and faster highway speeds — all of which raise fuel consumption. Typical real-world economy runs 10–25% below the combined sticker estimate. Use your measured figure (miles ÷ gallons) for budgeting, since that is what you actually achieve.
What does the MPG Calculator do?
Calculates your vehicle's real fuel economy. Enter the miles driven and the gallons of fuel used, and the tool returns MPG, litres per 100 km, and kilometres per litre, with a note on how your driving style and conditions affect the result. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the MPG Calculator use?
It computes MPG = miles driven ÷ gallons used, where gallons is the amount that refilled the tank. Enter the trip distance and the fuel pumped and the tool returns your fuel economy, plus the equivalent L/100km. For example, 350 miles on 12 gallons gives about 29.2 MPG.
Is the MPG Calculator free and private?
Yes — the MPG Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the MPG Calculator?
The MPG Calculator applies the standard formula: MPG = miles driven ÷ gallons of fuel used; L/100km = 235.215 ÷ MPG. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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