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Fuel Economy Converter

Swap US MPG, imperial MPG, liters per 100 km, and kilometers per liter without spreadsheet macros.

About Fuel Economy Converter

Fuel economy is reported in at least four units around the world: miles per gallon US (MPG US), miles per gallon Imperial (MPG UK), kilometres per litre (km/L), and litres per 100 kilometres (L/100km). Comparing across these is trickier than it looks. The US gallon holds 3.785 litres while the Imperial gallon holds 4.546 litres, making UK MPG about 20 percent higher than US MPG for the same car. L/100km is an inverse unit — lower means more efficient, opposite of MPG — so you cannot simply divide or multiply without the correct formula. This fuel economy converter handles all four units simultaneously. Enter a value in any unit and instantly see the equivalent in every other unit. You can also enter a fuel price to estimate cost per kilometre or mile, which makes trip budgeting or fleet benchmarking straightforward.

Why use Fuel Economy Converter

US vs UK Gallon Handled Correctly

The US gallon (3.785 L) and the Imperial gallon (4.546 L) are about 20 percent apart. Many online converters conflate them. This tool keeps both distinct, so a US-spec car's 30 MPG maps to the right UK-equivalent figure rather than an inflated one.

Inverse L/100km Logic

Litres per 100 km is an inverse efficiency measure — lower is better, the opposite of MPG. The converter applies the reciprocal formula correctly so you never accidentally rank a thirsty car as efficient.

Live Multi-unit Output

Change any one field and all three other units update immediately. There is no submit button and no page reload. You can iterate through scenarios — different fuel prices, different trip lengths — without retyping.

km/L for Asian and Indian Markets

Kilometres per litre is the dominant fuel-economy unit across India, Japan, and much of Southeast Asia. This converter treats km/L as a first-class input, not an afterthought, so regional comparisons are natural.

Trip Cost Estimation

Enter a local fuel price and the tool calculates your cost per kilometre or per mile in real time. This turns an abstract efficiency figure into a concrete budget number for road trips or fleet planning.

Fully Private, Offline Capable

All calculations happen in JavaScript in your browser. No values are transmitted to any server, no account is needed, and the tool continues working after the page loads even if connectivity drops.

How to use Fuel Economy Converter

Select the source unit from the dropdown: MPG (US), MPG (UK), km/L, or L/100km
Type your fuel economy value into the input field
Read the converted values for all three other units, which update instantly
Optionally enter a fuel price per litre or gallon to calculate cost per distance
Compare your result against the reference benchmarks displayed below the calculator
Click the copy button to copy any individual result to your clipboard

When to use Fuel Economy Converter

When comparing a US-spec car's EPA rating against a European WLTP figure for the same model
When budgeting fuel costs for a road trip across a country that uses different economy units
When evaluating a used vehicle listing that states economy in an unfamiliar unit
When a fleet manager needs to benchmark vehicles from multiple markets side by side
When a manufacturer's brochure gives km/L and you need MPG to compare against local competitors
When verifying that a quoted fuel economy figure converts correctly before committing to a lease or purchase

Examples

US MPG to all units

Input: 30 MPG (US)

Output: 36.03 MPG (UK) · 12.75 km/L · 7.84 L/100km

L/100km to all units

Input: 5 L/100km

Output: 47.04 MPG (US) · 56.50 MPG (UK) · 20.00 km/L

km/L to all units

Input: 25 km/L

Output: 58.80 MPG (US) · 70.62 MPG (UK) · 4.00 L/100km

Tips

L/100km is inverse — lower means better; this is the opposite of MPG where higher is better
US gallon (3.785 L) and UK gallon (4.546 L) differ by about 20%, so UK MPG always reads higher for the same car
Most modern compact petrol cars fall in the 5–7 L/100km range (33–47 MPG US); SUVs are typically 9–14 L/100km
Real-world fuel economy is usually 10–15% worse than official EPA or WLTP test-cycle ratings
EV efficiency uses kWh per 100 km or miles per kWh — a different unit family not covered by this converter

Frequently Asked Questions

What is the difference between US and UK MPG?▾

The US gallon is 3.785 litres, while the Imperial (UK) gallon is 4.546 litres. A car that achieves 30 MPG on the US scale achieves approximately 36 MPG on the UK scale. The vehicle's actual fuel consumption is identical — only the gallon definition differs.

Why does L/100km go up when efficiency goes down?▾

Litres per 100 km measures how much fuel you consume to travel a fixed distance, so a higher number means more fuel burned. It is the inverse of MPG, where a higher number means better efficiency. Dividing 235.2 by the L/100km value gives you the US MPG equivalent.

What does km/L mean?▾

Kilometres per litre tells you how far a vehicle travels on one litre of fuel, analogous to US MPG but using metric units. It is the standard efficiency measure in India, Japan, and many Asian markets. Higher is more fuel-efficient.

How do I compare a US-spec car against an EU-spec one?▾

Enter the US car's MPG (US) value in this tool to get the L/100km equivalent, then compare directly against the EU car's WLTP figure. Note that real-world consumption typically runs 10–15% higher than official test-cycle ratings for both markets.

Is 30 MPG good?▾

For a typical petrol passenger car in the US, 30 MPG (US) is above average and represents roughly 7.8 L/100km. Compact sedans and hybrids commonly exceed 35–40 MPG; full-size trucks and SUVs average 18–22 MPG. Context — vehicle class, load, driving style — matters most.

How do hybrids and EVs report efficiency?▾

Plug-in hybrids report both MPG (for the petrol engine) and MPGe (miles per gallon equivalent for electric mode). Battery electric vehicles use kWh per 100 km or miles per kWh — a different energy unit family. This tool covers liquid-fuel units; EV kWh figures require a separate energy converter.

How does air conditioning affect fuel economy?▾

Running the air conditioning typically reduces real-world fuel economy by 5–25% depending on ambient temperature, vehicle size, and compressor load. EPA and WLTP test cycles include some AC usage, but hot-climate real-world figures can be notably worse than the label.

What is the exact formula for converting MPG (US) to L/100km?▾

Divide 235.214583 by the MPG (US) value. For example, 30 MPG (US) equals 235.214583 ÷ 30 = 7.84 L/100km. The constant comes from converting miles to kilometres and US gallons to litres in one step.

Explore the category

Glossary

Miles Per Gallon (MPG): A fuel economy measure stating how many miles a vehicle travels on one gallon of fuel. Higher values indicate greater efficiency. The US and UK versions differ because their gallons have different volumes.
US Gallon: The liquid gallon used in the United States, equal to 3.785 litres. It is smaller than the Imperial gallon, so US MPG figures are always lower than UK MPG for the same vehicle.
Imperial Gallon: The gallon used in the United Kingdom and some Commonwealth countries, equal to 4.546 litres. Because it is larger than the US gallon, UK MPG figures are approximately 20% higher than the US equivalent.
Litres per 100 km (L/100km): A fuel consumption measure stating how many litres of fuel are needed to travel 100 kilometres. It is the standard unit in Continental Europe, Canada, and Australia. Lower is more efficient, making it the inverse of MPG.
Kilometres per Litre (km/L): A fuel economy measure stating how far a vehicle travels on one litre of fuel. It is the dominant unit in India, Japan, and Southeast Asia. Higher values indicate greater efficiency.
Fuel Economy: A measure of how efficiently a vehicle uses fuel over a given distance. It is expressed as distance per unit volume (MPG, km/L) or volume per unit distance (L/100km). Official figures come from standardised test cycles such as EPA (US) or WLTP (Europe).