Calculator
What the Gallon per Mile Converter does
Gallon per Mile Converter: converts Gallons per 100 miles (US) to Litres per 100 km through fuel economy's base unit, so the result is exact rather than rounded. Example: 8 gal/100mi = 18.81716664 L/100km.
Supply Value, From and To and you get Result, How it was calculated and Reverse conversion back. The result recalculates on every keystroke without a button press or a page reload.
It is mostly used by anyone working across two measurement systems. Having the exact factor matters more than a rough mental estimate.
Everything happens inside this page. Nothing you type is sent to a server, and there is nothing for us to store.
The rest of this page documents each field, the method, and a worked example built from the values the gallon per mile converter loads by default.
What do the Gallon per Mile Converter fields mean?
The Gallon per Mile Converter uses 3 inputs. The defaults are there to be replaced. They exist so the tool is never showing an empty result.
| Field | What to enter | Default |
|---|---|---|
| Value | required | 8 |
| From | choose from Litres per 100 km (L/100km), Kilometres per litre (km/L), Miles per gallon (US) (mpg (US)), Miles per gallon (imperial) (mpg (imp)), Miles per litre (mi/L) or Gallons per 100 miles (US) (gal/100mi) | Gallons per 100 miles (US) (gal/100mi) |
| To | choose from Litres per 100 km (L/100km), Kilometres per litre (km/L), Miles per gallon (US) (mpg (US)), Miles per gallon (imperial) (mpg (imp)), Miles per litre (mi/L) or Gallons per 100 miles (US) (gal/100mi) | Litres per 100 km (L/100km) |
How does the Gallon per Mile Converter work?
Because they are reciprocals, you cannot convert between them by multiplying: halving gal/100mi does not halve L/100km. The conversion goes through litres per 100 km, and small differences matter: the US and imperial gallons are not the same size.
The constants come from the SI brochure and the 1959 international yard-and-pound agreement. For quantities defined empirically rather than by treaty, the current CODATA or IAU value is used instead.
Worked example
These are the values the Gallon per Mile Converter loads by default, and the result it produces from them. These are the tool’s own default values and the result they produce, not an invented illustration.
| Value | 8 |
|---|---|
| From | Gallons per 100 miles (US) (gal/100mi) |
| To | Litres per 100 km (L/100km) |
| Result | 18.81716664 L/100km |
|---|---|
| How it was calculated | 8 gal/100mi → 18.81716664 L/100km (via L/100km) |
| Reverse conversion | 3.401149664 gal/100mi (if you meant 8 L/100km) |
Gallons per 100 miles
Gallons per 100 miles (like L/100km) measures fuel consumed per fixed distance rather than distance travelled per unit of fuel: flipping the usual US mpg convention around specifically to avoid the mathematical distortions that mpg’s inverse relationship causes.
Worth knowing
- Because it scales linearly with actual fuel consumption, gallons-per-100-miles is the preferred metric in some US fuel-economy and emissions policy analysis, precisely because it can be meaningfully averaged and compared across a mixed fleet of vehicles in a way raw mpg figures cannot.
- The efficiency gap between a 10 mpg and a 20 mpg vehicle represents a far larger real fuel saving than the gap between a 40 mpg and a 50 mpg vehicle, even though both pairs are "10 mpg apart". Expressing consumption in gallons per fixed distance makes that real-world difference immediately visible, which is exactly why mpg alone can be a misleading efficiency metric for policy purposes.
- This unit isn’t commonly seen in consumer-facing marketing (mpg remains the familiar figure to most US drivers), but it’s a genuinely more mathematically honest way to compare fuel consumption, which is why it appears in more technical and policy contexts.
Definitions: BIPM SI Brochure · NIST reference on units
How to use it
- Put Value.
- Pick a value for From: the options are Litres per 100 km (L/100km), Kilometres per litre (km/L), Miles per gallon (US) (mpg (US)), Miles per gallon (imperial) (mpg (imp)), Miles per litre (mi/L) or Gallons per 100 miles (US) (gal/100mi).
- Pick a value for To: the options are Litres per 100 km (L/100km), Kilometres per litre (km/L), Miles per gallon (US) (mpg (US)), Miles per gallon (imperial) (mpg (imp)), Miles per litre (mi/L) or Gallons per 100 miles (US) (gal/100mi).
- The output refreshes live, so you can stop as soon as the number looks right.
- The results panel then shows Result, How it was calculated and Reverse conversion.
- Both Copy Link and Print capture the current state, so pick whichever suits how you file things.
What this tool does not do
- Repeated conversions compound rounding, so convert once from the original value where possible.
- Factors use the internationally agreed definitions; some industries round them differently.
- The method is fixed. There is no option to substitute your own formula.
- Read the field labels once before trusting the answer; they specify the expected unit.
Frequently asked questions
You need Value, From and To. A starting value is in place for each, letting you treat it as a what-if tool rather than a data-entry form.
With the values loaded when the page opens, result comes out as 18.81716664 L/100km. It recalculates the moment an input changes, which makes comparing scenarios quick.
Nothing is stored. The page has no back end to send data to, and holds your input only in memory.
It costs nothing, and there is no limit on repeat use.
The conversion is exact for the method described above. Where a value is rounded for display, the underlying figure keeps full precision.