When the Fuel Economy Converter seems to misbehave, the cause is usually one of two things: something stopped the tool from running, or it ran but the result is not usable. This guide starts with the fastest checks, then walks through the common problems and exact fixes.
Quick Checks First
- Refresh the page - a stalled session is the most common cause of nothing happening.
- Confirm the input is not empty and actually contains what you meant to submit.
- Try the smallest possible input; if that works, the issue is size, not the tool.
- Turn off browser extensions that block scripts, then reload and test again.
- Update or switch browsers if the problem repeats across sessions.
Common Problems and How to Fix Them
My converted figure looks inverted.
Litres per 100 km works backwards - a smaller number means a more efficient car, unlike mpg.
US and UK mpg differ in the listing.
An imperial gallon is larger, so UK mpg numbers run higher - the tool asks which gallon the source uses.
The two conversions do not round-trip.
The relationship is reciprocal rather than linear - small rounding at each step is normal, so keep decimals.
City and highway numbers do not match.
Convert each figure separately - averaging efficiency numbers first distorts the real result.
I want cost, not just economy.
Pair the converted figure with your fuel price and distance - our fuel cost calculator covers that step.
My readings may be stored somewhere.
No - the conversion runs in your browser with nothing saved.
When It Works but the Output Is Poor
If the tool runs fine but the result misses, the problem is almost always the brief, not the software:
- Assuming higher l per 100 km is better
- Mixing US and UK gallons
- Treating mpg as a linear scale
- Comparing city and highway figures together
How to Stop It Happening Next Time
- Keep a saved prompt template for every task you repeat.
- Change one setting per generation so causes stay obvious.
- Run a two-minute sanity test with known input after any update.
- Note every failure and its fix; a short troubleshooting log pays for itself.
Still Stuck?
Reproduce the problem with the smallest possible input and note the exact steps that triggered it. A one-line description of what you did, what you expected and what happened is enough to get a precise answer from support or a colleague.
Frequently Asked Questions
Which fuel economy units are supported?
Miles per gallon, litres per 100 kilometres and kilometres per litre, the three common efficiency measures.
How do I convert mpg to l per 100 km?
Divide 235.215 by the mpg figure - so 25 mpg becomes about 9.41 litres per 100 kilometres.
Does it use US or UK gallons?
Both are handled - tell the tool which gallon your mpg figure came from, since the imperial gallon is larger.
Is my input stored?
No - everything runs in your browser.
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