Fuel economy converter: L/100km, mpg US and UK
Fuel math is a reciprocal: 6 L/100km is 39.20 mpg US and 47.08 mpg UK, because US and imperial gallons differ (3.785 L vs 4.546 L). Europe counts litres per 100 km (less is better), the US and UK count miles per gallon (more is better). This calculator is built for fast, private, offline use in your browser. Every formula runs locally and is verified against official sources. You enter the key numbers, see the result instantly and check the steps.
TL;DR
- mpg US = 235.215 ÷ L/100km; mpg UK = 282.481 ÷ L/100km; back with the same constants.
- Formulas: mpg = const ÷ L/100km | L/100km = const ÷ mpg (US 235.215, UK 282.481)
- Example 1: 6 L/100km in mpg — US: 235.215÷6 = 39.20 mpg
How it works
mpg US = 235.215 ÷ L/100km; mpg UK = 282.481 ÷ L/100km; back with the same constants. Pick US or UK gallons first, they differ by 20%. Start with clean data, keep the same units and follow the order in the formula. The tool does the arithmetic, you choose rate, period or factor. A second example with different numbers shows how the result scales.
The math
6 L/100km gives 235.215÷6=39.20 mpg US and 282.481÷6=47.08 mpg UK. Back: 30 mpg US gives 235.215÷30=7.84 L/100km; 40 mpg UK gives 282.481÷40=7.06 L/100km.
UK gallons are bigger, so UK mpg reads ~20% higher for the same car.
Examples
Example 1: 6 L/100km in mpg
- US: 235.215÷6 = 39.20 mpg
- UK: 282.481÷6 = 47.08 mpg
- Same car, two numbers: gallons differ
Example 2: 30 mpg US and 40 mpg UK back to L/100km
- US: 235.215÷30 = 7.84 L/100km
- UK: 282.481÷40 = 7.06 L/100km
- UK figure converts to less fuel per 100 km
When to use it
✦ US import sticker
Read an American window sticker in European units: mpg to L/100km.
✦ UK car reviews
Compare British reviews (imperial mpg) with EU figures: convert both ways.
⚠ Common mistakes
- US vs UK gallons: 30 mpg US is not 30 mpg UK, they differ by 20%.
- Reading L/100km backwards: lower is better, unlike mpg.
- Rounding the constant: 235.215 vs 235 changes the second decimal.
FAQ (6)
6 L/100km in mpg?
39.20 mpg US or 47.08 mpg UK.
Why is UK mpg higher?
The imperial gallon (4.546 L) is bigger than the US gallon (3.785 L).
If I type my salary or prices here, do you store them?
No — and that's deliberate. Everything runs locally in your browser, nothing leaves your device. We don't see your net salary, your margins, or the VAT numbers you test. For a finance tool that matters: you can run a quick check on a payslip or an invoice while on public Wi-Fi and close the tab knowing no trace is kept server-side.
Can I use it on the train without signal to check an invoice?
Yes. Load the page once, then it works offline. VAT, discount and mortgage math are all pure JavaScript — no API call. I often test it in airplane mode: open the mortgage page, type 250,000 at 4.5% for 25 years, you get the schedule instantly, even in a tunnel.
Can I file taxes with these results?
Use it as a fast sanity check, not as the final filing. Formulas are standard (e.g. Net = Gross / 1+VAT) and verified against official sources listed at the bottom, but rates and thresholds change — Italy's 22% vs Germany's 19%, or IRPEF brackets. For the actual declaration, double-check with your accountant or Agenzia delle Entrate / HMRC / IRS.
How do I send a calculation to my accountant?
Hit 'Share Link' under the results. It encodes the inputs in the URL — e.g. ?price=1200&vat=22 — so your accountant opens the exact same view, no screenshot needed. You can also copy the result with one tap and paste it into an email.
Sources & References
How this calculator is maintained
This calculator is written and maintained by Davide Coronese, independent developer and founder of CalcTracker.
Methodology: every formula is checked against official publications and validated by an automated test suite before release. Health, tax and finance pages cite the exact sources they rely on.
Found an error? Contact us — verified corrections ship within 24 hours.