Fuel Efficiency Calculator

How to Use This Calculator

This fuel efficiency calculator converts any distance and fuel amount into all four major efficiency units at once. You do not need to know which unit you want in advance.

1. Distance traveled: Enter how far you drove. Choose miles if you are in the US or UK, or km if you are in Canada, Europe, or Australia.
2. Fuel used: Enter how many gallons or litres you consumed. The fill-up amount on your receipt is the easiest source. Select US gallons, UK/imperial gallons, or litres.
3. Fuel price (optional): Enter the price per gallon or per litre to unlock the cost per 100 km and cost per 100 miles outputs.
4. Read results: The calculator displays MPG (US), MPG (UK), L/100km, and km/L simultaneously, along with a step-by-step breakdown of how each figure was derived.

The fastest way to use this as a car fuel efficiency calculator is to note your odometer reading when you fill up, then note it again at the next fill-up. Subtract the first from the second to get your distance. Enter that distance and the number of gallons or litres you just added to the tank.

What Is Fuel Efficiency?

Fuel efficiency is a measure of how far a vehicle can travel on a given amount of fuel. A more fuel-efficient car covers more distance per gallon or per litre, which directly reduces running costs and carbon emissions.

The term appears under several names depending on the field: fuel economy, fuel consumption, and miles per gallon all describe the same underlying ratio of distance to fuel. The difference is just in which number sits on top of the fraction.

In the US, higher numbers are better because MPG measures distance per unit of fuel. In Europe and Canada, lower numbers are better because L/100km measures fuel used per unit of distance. This difference trips up a lot of people when comparing vehicles across different markets.

Car manufacturers, governments, and environmental agencies all track fuel efficiency because transport accounts for roughly 16% of global CO2 emissions. Small improvements in average vehicle efficiency across a fleet translate into significant reductions at scale.

How to Calculate Fuel Efficiency

There are four common units for fuel efficiency, and each has its own formula. All four are derivable from a single pair of inputs: distance traveled and fuel consumed.

Miles Per Gallon (MPG US)

The US standard. Divide the number of miles driven by the number of US gallons used:

A US gallon is 3.785 litres. If you have data in km and litres, the full conversion is: MPG (US) = (km / 1.60934) / (liters / 3.78541). This calculator handles that automatically.

Litres Per 100 Kilometres (L/100km)

The standard for Canada, Europe, Australia, and most of Asia. It measures how many litres are consumed per 100 km of travel:

Because this is fuel per distance (not distance per fuel), a lower number means better efficiency. A car using 6 L/100km is more efficient than one using 10 L/100km. To convert from MPG (US): L/100km = 235.215 / MPG (US).

Kilometres Per Litre (km/L)

Common in India, Japan, the Philippines, and some other Asian markets. It is the metric analogue of MPG: higher is better.

The relationship between km/L and L/100km is clean: km/L = 100 / L/100km. A car that gets 12.5 km/L uses exactly 8.0 L/100km.

UK / Imperial MPG

The United Kingdom uses MPG, but with imperial gallons (4.546 litres each rather than the US 3.785). An imperial gallon is about 20% larger, so UK MPG figures are always about 20% higher than US MPG figures for the same vehicle:

A car rated at 40 MPG in the UK is roughly equivalent to 33 MPG in the US. When comparing cars across markets, always check which gallon is being used. The conversion factor is: MPG (UK) = MPG (US) x 1.20095.

Fuel Efficiency Unit Conversion Table

Use this table as a quick fuel efficiency comparison tool when reading international car reviews or spec sheets:

The key relationship to remember: MPG (US) x L/100km = 235.215. That single constant lets you convert between the two most common systems with one division.

Fuel Efficiency by Country

This vehicle fuel efficiency calculator supports every major unit, which is useful because the same car is advertised with entirely different numbers depending on the market.

United States

The US uses MPG with US gallons. The Environmental Protection Agency (EPA) tests and publishes fuel economy ratings for all new vehicles. The combined cycle figure (55% city, 45% highway) is what appears on the window sticker. Real-world fuel efficiency is typically 10-20% lower than the EPA estimate due to aggressive driving, air conditioning use, and cold weather.

United Kingdom and Ireland

The UK historically used MPG with imperial gallons. Since the WLTP (Worldwide Harmonised Light Vehicles Test Procedure) replaced NEDC testing in 2018, official figures are generally closer to real-world use. UK motorists looking to compare against US-spec cars should divide the UK MPG figure by 1.20095 to get the equivalent US MPG.

Canada, Australia, and Europe

These markets use L/100km. Natural Resources Canada publishes fuel consumption ratings for all vehicles sold in Canada. The Australian Government uses a combined cycle figure similar to the WLTP. The EU's official figures follow WLTP since September 2017.

India, Japan, and the Philippines

India officially reports efficiency in km/L (also written as kmpl). The ARAI (Automotive Research Association of India) tests all vehicles sold in India. Japan uses km/L as well. The Philippines uses km/L informally, though official figures sometimes appear in L/100km. To convert: km/L = 100 / L/100km.

What Is Good Fuel Efficiency for a Car?

What counts as good depends heavily on vehicle class. A large pickup truck with 20 MPG (US) is considered reasonable for its segment, while a compact car returning 20 MPG would be poor by today's standards.

As a practical rule of thumb, any car consistently above 35 MPG (US) / below 6.7 L/100km is doing well in the global context. Below 25 MPG / above 9.4 L/100km is where operating costs start to matter significantly at current fuel prices.

A useful way to assess efficiency improvement is with the Percentage Decrease Calculator: if your car went from 26 MPG to 32 MPG after maintenance, that is a 23% efficiency gain. Use the Flight Distance Calculator to estimate total km for long trips, which feeds directly into the fuel cost section here.

Worked Examples

Example 1: 2024 Toyota Camry (US fill-up)

You fill up your 2024 Toyota Camry Hybrid. The odometer read 18,400 miles at the last fill-up and reads 18,732 miles now. You put in 9.4 US gallons.

• Distance: 18,732 - 18,400 = 332 miles
• MPG (US) = 332 / 9.4 = 35.3 MPG
• L/100km: 235.215 / 35.3 = 6.67 L/100km
• km/L = 35.3 x 0.4251 = 15.0 km/L

This is right in line with the Camry Hybrid's EPA combined rating of 37 MPG. The slight shortfall is typical for mixed city/highway driving.

Example 2: European road trip (L/100km)

You drive 480 km on the Autobahn in Germany and use 38.4 litres of diesel.

• L/100km = (38.4 / 480) x 100 = 8.0 L/100km
• km/L = 100 / 8.0 = 12.5
• MPG (US) = 235.215 / 8.0 = 29.4 MPG
• MPG (UK) = 29.4 x 1.20095 = 35.3 MPG

The high speed driving (130+ km/h) explains why this is above 8 L/100km even for a modern diesel. Most diesel cars achieve 5-6 L/100km at 90 km/h.

Example 3: Motorcycle (UK fuel receipt)

A UK motorcycle rider fills up after 180 miles and puts in 3.2 UK gallons (imperial).

• MPG (UK) = 180 / 3.2 = 56.3 MPG (UK)
• MPG (US) = 56.3 / 1.20095 = 46.9 MPG (US)
• L/100km = 235.215 / 46.9 = 5.01 L/100km

Motorcycles typically outperform cars in L/100km terms because of their lower weight. A 56 MPG UK motorcycle would look like 46.9 MPG to an American reader.

Example 4: Indian hatchback (km/L)

A Maruti Suzuki Swift in Bengaluru covers 620 km on 48 litres of petrol.

• km/L = 620 / 48 = 12.9 km/L
• L/100km = 100 / 12.9 = 7.75 L/100km
• MPG (US) = 235.215 / 7.75 = 30.4 MPG

The ARAI-certified figure for the Suzuki Swift petrol is around 21-23 km/L, so real-world city driving at 12.9 km/L reflects the typical urban penalty.

Example 5: Comparing two cars with the conversion table

You are choosing between Car A (US spec, 31 MPG combined) and Car B (European spec, 7.2 L/100km combined). Which is more efficient?

• Car A: 31 MPG (US) = 235.215 / 31 = 7.59 L/100km
• Car B: 7.2 L/100km = 235.215 / 7.2 = 32.7 MPG (US)

Car B is slightly more efficient (7.2 vs 7.59 L/100km). Without converting to a common unit, the comparison is meaningless. This is exactly what the fuel efficiency comparison calculator tab above is designed to make instant.

Frequently Asked Questions

How do I calculate fuel efficiency at home?

Fill your tank to full and note the odometer reading. Drive normally until your next fill-up, then note the odometer again and fill to full. Divide the miles (or km) driven by the fuel you just added. That gives you your real-world MPG or L/100km for that interval. This is far more accurate than any short-trip estimate because it averages out cold-start penalties, city traffic, and highway cruising.

How to calculate fuel efficiency in miles per gallon?

MPG = miles driven / US gallons used. For example, if you drove 350 miles and used 11.5 gallons, your MPG = 350 / 11.5 = 30.4. If your fuel receipt is in litres, convert first: litres / 3.78541 = US gallons. Then apply the same formula. This calculator does the conversion automatically when you select "Liters" as the fuel unit and "miles" as the distance unit.

What is the difference between MPG (US) and MPG (UK)?

Both use miles in the numerator, but they differ on gallons: a US gallon is 3.785 litres while a UK/imperial gallon is 4.546 litres. The UK gallon is about 20% larger, so MPG (UK) is always about 20% higher than MPG (US) for the same vehicle. A car rated 50 MPG in Britain is only about 41.6 MPG by the US measure. Always check which gallon is being used before comparing cars across markets.

How do I convert MPG to L/100km?

Use the constant 235.215: L/100km = 235.215 / MPG (US). For example, 30 MPG (US) = 235.215 / 30 = 7.84 L/100km. Going the other way: MPG (US) = 235.215 / L/100km. This number comes from the number of litres in 100 miles (1 US gallon = 3.78541 L; 100 miles = 160.934 km; 160.934 / 3.78541 x 3.78541 simplifies to 235.215).

What is good fuel efficiency for a car?

For a typical passenger car in 2024, 35+ MPG (US) / under 6.7 L/100km is considered good. Compact hybrids like the Toyota Prius achieve 50+ MPG (US). The US new-vehicle fleet average was about 29 MPG in 2023. In European terms, under 6 L/100km is good for a midsize car; the EU fleet average target is 4.1 L/100km (57 MPG US) by 2030.

Does driving speed affect fuel efficiency?

Yes, significantly. Most petrol and diesel cars peak efficiency at 80-95 km/h (50-60 mph). Above that, aerodynamic drag increases with the square of speed, so fuel consumption rises sharply. Driving at 120 km/h typically uses 20-30% more fuel than driving at 90 km/h. Cold weather also reduces efficiency because engines take longer to warm up and battery-powered systems draw more power.

How do I improve my car fuel efficiency?

The biggest gains come from driving style: smooth acceleration, anticipatory braking, and avoiding idling. After that: keep tyres at the correct pressure (under-inflation adds rolling resistance), remove roof racks when not in use, and service the engine on schedule. A dirty air filter, worn spark plugs, or low tyre pressure can each cost 2-5% in efficiency. Trip planning helps too: combining short errands into one warm-engine run is far more efficient than multiple cold starts.

How do I calculate fuel efficiency of a bike?

The fuel efficiency calculation for a bike (motorcycle or bicycle with a motor) is identical to a car: miles / gallons or km / litres. Motorcycles tend to achieve 45-70 MPG (US) because of their low weight. For a pedal-assist e-bike, manufacturers quote range per charge rather than fuel efficiency, but the watt-hours per km calculation follows the same distance-divided-by-energy structure.

How does Google Maps estimate fuel efficiency?

Google Maps uses an average fuel economy figure for your selected vehicle type and the route's speed profile (city vs highway proportions). It multiplies estimated fuel consumption by the current average pump price in your region. The estimate is a rough guide: your actual result will differ based on your specific car, driving style, and load. For a precise fuel cost calculation, use your measured real-world efficiency here instead.

What is a fuel efficiency calculator for Canada?

In Canada, fuel efficiency is expressed in L/100km, and fuel prices are per litre. Enter your distance in km, your fuel used in litres, and optionally enter the price per litre in the cost field. The calculator will give you L/100km directly as the primary result and also show you the equivalent MPG figures for comparison with US or UK cars. Natural Resources Canada's fuel consumption guide is updated annually and uses city and highway figures separately.

What is the formula for vehicle fuel efficiency calculation?

The core formula is: efficiency = distance / fuel. In practice: MPG = miles / US gallons, L/100km = (litres / km) x 100, km/L = km / litres, MPG (UK) = miles / UK gallons. All four are derived from the same two measurements. The interconversions are: L/100km = 235.215 / MPG (US), km/L = MPG (US) x 0.4251, MPG (UK) = MPG (US) x 1.2009. Enter any distance and fuel amount here to get all four values at once.

References

• US Department of Energy, Fuel Economy Guide, fueleconomy.gov: source for EPA MPG ratings and fuel economy testing methodology for US-market vehicles.
• Natural Resources Canada, Fuel Consumption Guide, nrcan.gc.ca: annual guide covering L/100km ratings for all vehicles sold in Canada.
• European Environment Agency, CO2 Emissions from New Passenger Cars, eea.europa.eu: data on EU fleet average fuel efficiency and CO2 emissions trends under the WLTP test cycle.