Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Miles per gallon
28.07
Liters per 100 km
8.38
Kilometers per liter
11.93
Fuel cost per mile
$0.128
Cost of this fill-up
$41.04
Fuel cost per 100 miles
$12.83
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter miles driven since last fill.
- 2Enter gallons to refill.
- 3Enter price per gallon ($).
- 4Read your miles per gallon on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Measure economy across a full tank, not a single trip: fill up, reset the trip meter, then divide miles driven by gallons at the next fill for a real number.
Worked example
Using the values the calculator loads with:
Inputs
- Miles driven since last fill: 320
- Gallons to refill: 11.4
- Price per gallon: 3.6 $
Results
- Miles per gallon: 28.07
- Liters per 100 km: 8.38
- Kilometers per liter: 11.93
- Fuel cost per mile: $0.128
- Cost of this fill-up: $41.04
- Fuel cost per 100 miles: $12.83
What each field means
Inputs
- Miles driven since last fill
- The miles driven since last fill used in the calculation. Starts at 320 so you have a working example on load.
- Gallons to refill
- The gallons to refill used in the calculation. Starts at 11.4 so you have a working example on load.
- Price per gallon ($)
- The price per gallon used in the calculation, measured in $. Starts at 3.6 $ so you have a working example on load.
Results
- Miles per gallon
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Liters per 100 km
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Kilometers per liter
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Fuel cost per mile
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cost of this fill-up
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Fuel cost per 100 miles
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the mpg (fuel economy) calculator work?
Measure economy across a full tank, not a single trip: fill up, reset the trip meter, then divide miles driven by gallons at the next fill for a real number. The underlying maths is: MPG = Miles driven ÷ Gallons used; L/100km = 235.215 ÷ MPG.
What do I need to enter?
3 values: miles driven since last fill, gallons to refill, and price per gallon. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the miles per gallon result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). MPG Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/mpg
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/mpg" target="_blank" rel="noopener">MPG Calculator — RevenueLab</a> (2026).</p>
Source: [MPG Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/mpg) (2026).