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Mileage Calculator | Track Fuel Economy, Cost Per Mile, and Trips

Quick reference

Fuel cost per 100 miles (gas at $3.50/gal):

MPG	Gallons/100mi	Cost/100mi
20	5.00	$17.50
30	3.33	$11.67
40	2.50	$8.75
50	2.00	$7.00

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Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.

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No newsletter pop-ups, no "create an account to see the answer", no fake countdown, no fake stock counter, no upsell. Two ad slots per page (clearly labelled as Advertisement) keep the site free — that's the whole business model.

Interpretation guide

Reading your numbers:

Metric	What it means
MPG	Miles driven per gallon — higher is better
L/100km	Liters per 100 km — lower is better
Cost per mile	Fuel spend divided by miles driven
Reimbursement	Business miles x the IRS standard rate

lightbulb Worked example — tank-to-tank MPG

You drive 320 miles on a tank, then refill with 12.5 gallons. MPG = 320 ÷ 12.5 = 25.6. Metric equivalent: L/100km = 235.215 ÷ 25.6.

Result: 25.6 MPG ≈ 9.2 L/100km.

What this means: At $3.50/gallon that's 13.7¢ per mile. If your MPG suddenly drops ~10% on the same commute, check tire pressure and the air filter before suspecting anything expensive — those are the usual culprits.

Formula & methodology

Formula: MPG = Miles / Gallons; L/100km = (Liters / km) x 100; Cost per mile = Fuel cost / Miles

How fuel economy is computed

MPG = miles driven ÷ gallons used. Metric economy: L/100km = 235.215 ÷ MPG (the exact US-gallon constant). Cost per mile = total fuel cost ÷ miles driven.

Track tank-to-tank over several fill-ups — single tanks vary with pump cut-off.
A sudden ~10% MPG drop on a familiar route often means low tire pressure or a clogged air filter.

MPG measures efficiency; cost per mile measures money — the same 25-MPG car costs 14¢/mile at $3.50/gal but 20¢/mile at $5/gal.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate my car's MPG?

Enter the required values into the input fields and press the calculate button. The tool applies the formula MPG = Miles / Gallons; L/100km = (Liters / km) x 100; Cost per mile = Fuel cost / Miles and returns the result with a short explanation of each step, so you can check the working yourself.

How do I convert MPG to L/100km?

Use the reciprocal conversion: L/100km = 235.215 ÷ MPG. A car getting 30 MPG uses about 7.84 L/100km, and 40 MPG is about 5.88 L/100km. The factor 235.215 comes from the units: 100 km ÷ (1.609 km/mile) ÷ (1 gallon ÷ 3.785 L) × 1 MPG. The calculator converts in both directions.

What is a good MPG?

The Mileage 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. Tracks your vehicle's fuel economy and trip costs. Enter the odometer reading, or the miles driven and fuel used, and the tool calculates MPG, litres per 100 km, and the cost per mile or kilometre, plus the estimated fuel cost of your regular trips. There is no limit on usage, and it works on any device.

How do I find cost per mile?

Yes — the Mileage 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 do I calculate mileage reimbursement?

Multiply the business miles driven by the reimbursement rate: reimbursement = miles × rate per mile. The IRS standard rate (about 67¢ per mile in 2024, adjusted annually) covers fuel, maintenance, depreciation, and insurance. The calculator returns the reimbursement amount for any rate, so you can also compare the IRS rate with your employer's rate.

What's the difference between MPG and cost per mile?

MPG measures efficiency (how far fuel takes you); cost per mile measures money. A 25-MPG car at $3.50/gal costs 14¢/mile, but the same car at $5/gal costs 20¢/mile with identical MPG. The calculator shows both, since fuel prices move independently of your car's efficiency.

Where does 235.215 come from?

It is the exact conversion constant: one US gallon is 3.78541 litres and one mile is 1.60934 km, so L/100km = 235.215 ÷ MPG. A 30-MPG car uses 7.84 L/100km. Note it only works with US gallons — imperial gallons need 282.481 instead.

Is my data sent anywhere when I calculate?

No — the math runs on the page itself, so your trip and fuel data never leave your device.

How precise is tank-to-tank MPG?

Typically within ±2–3% if you fill to the same pump cut-off each time. Single-tank readings bounce around with fill variation; averaging over 3–5 tanks smooths it out and reveals real trends like a slowly clogging air filter.

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