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Fuel Economy Converter

Converts fuel consumption between litres per 100 km, kilometres per litre, miles per US gallon and miles per imperial gallon; L/100km is the base and the mpg relations are reciprocal (L/100km = 235.214583 / mpg_US).

When to use

You need a car's fuel economy in another convention, e.g. mpg to L/100km, L/100km to km/L or US mpg to UK mpg.

Do not use when: You need the fuel cost of a trip (use fuel-cost) or plain volume or distance conversions (use volume, length).

Formula

L/100km = 100 / (km/L) = 235.214583 / mpg(US) = 282.480936 / mpg(UK); mpg(UK) = mpg(US) × 1.200950

Consumption (L/100km) and economy (km/L, mpg) are reciprocals, so the conversion is non-linear and no constant factor applies. Constants: 100 × 3.785411784 / 1.609344 = 235.214583 and 100 × 4.54609 / 1.609344 = 282.480936.

Inputs

Parameter	Type	Required	Description
`value`	number	yes	Fuel economy in from_unit (must be greater than 0). Range: > 0
`from_unit`	enum: L/100km \| km/L \| mpg_us \| mpg_uk	yes	Unit of the input value. Accepted symbols: L/100km, km/L, mpg_us, mpg_uk; spelled-out names and common abbreviations are accepted too.
`to_unit`	enum: L/100km \| km/L \| mpg_us \| mpg_uk	yes	Unit to convert into (same symbols as from_unit).

Outputs

Output	Type	Description
`result`	number	Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).
`result_text`	string	The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km".
`formula`	string	Relation used, e.g. "1 mi = 1.609344 km".
`factor`	number	Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.
`conversion_table`	object	The input value expressed in every supported fuel economy unit (6 significant figures), keyed by unit symbol.

Example

30 US mpg to L/100km: {"value":30,"from_unit":"mpg_us","to_unit":"L/100km"} → {"result":7.840486,"formula":"L/100km = 235.214583 / mpg (US)","conversion_table":{"km/L":12.7543,"mpg_uk":36.0285}}

6 L/100km to US mpg: {"value":6,"from_unit":"L/100km","to_unit":"mpg_us"} → {"result":39.202431,"conversion_table":{"km/L":16.6667,"mpg_uk":47.0802}}

GET https://tttkmbb.com/api/v1/calculate/fuel-economy?value=30&from_unit=mpg_us&to_unit=L%2F100km

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/fuel-economy (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/fuel-economy · Markdown: https://tttkmbb.com/conversion/fuel-economy.md · JSON definition: https://tttkmbb.com/conversion/fuel-economy.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="fuel-economy"
OpenAPI operationId: convert_fuel_economy
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Which mpg does 'mpg' mean?

The plain alias mpg resolves to miles per US gallon (mpg_us). UK figures use the larger imperial gallon: mpg_uk = mpg_us × 1.20095.

Why is lower L/100km better?

L/100km measures consumption, mpg and km/L measure economy; 5 L/100km = 20 km/L = 47.0 US mpg, and halving consumption doubles mpg.

Related calculators

Fuel Cost Calculator — Trip fuel cost from distance, consumption and price.
Volume Converter — Convert gallons and litres directly.
Length Converter — Convert miles and kilometres directly.