Convert between MPG (US & UK), L/100km, km/L, and other fuel efficiency units — instantly.
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This free fuel efficiency converter lets you instantly switch between MPG (US), MPG (UK), L/100km, km/L, and liters per mile — the five units used across every major automotive market. Whether you are comparing a European car's L/100km rating with an American model's MPG figure, working out fuel costs for a road trip abroad, or trying to decode a Japanese spec sheet in km/L, this tool gives you the exact conversion in one step.
Fuel economy is one of the most practically important numbers attached to any vehicle. A difference of just 5 MPG between two otherwise similar cars translates to hundreds of dollars in fuel savings each year and a measurably lower carbon footprint over the car's lifetime. Understanding how to read, compare, and convert these numbers across different regional standards is a skill every driver benefits from — and this guide covers everything you need to know.
Every fuel efficiency unit measures the same underlying relationship between fuel volume and distance traveled — but different countries frame it differently. Some units express how far you go per unit of fuel; others express how much fuel you burn per fixed distance. Knowing which direction the unit runs is essential before comparing figures.
All conversions flow through two physical constants: 1 mile = 1.60934 km, and 1 US gallon = 3.785411784 liters. Combining these gives the master constant 235.215 for US MPG, and 282.481 for UK MPG. For quick mental arithmetic, 235 and 282 are accurate to within 0.1%.
| Convert From | Convert To | Formula | Example |
|---|---|---|---|
| MPG (US) | L/100km | L/100km = 235.215 ÷ MPG | 30 MPG → 7.84 L/100km |
| L/100km | MPG (US) | MPG = 235.215 ÷ L/100km | 8.0 L/100km → 29.4 MPG |
| MPG (UK) | L/100km | L/100km = 282.481 ÷ MPG | 40 MPG(UK) → 7.06 L/100km |
| L/100km | MPG (UK) | MPG(UK) = 282.481 ÷ L/100km | 6.0 L/100km → 47.1 MPG(UK) |
| km/L | L/100km | L/100km = 100 ÷ km/L | 14 km/L → 7.14 L/100km |
| L/100km | km/L | km/L = 100 ÷ L/100km | 7.5 L/100km → 13.3 km/L |
| MPG (US) | km/L | km/L = MPG × 0.425144 | 35 MPG → 14.88 km/L |
| MPG (UK) | MPG (US) | MPG(US) = MPG(UK) × 0.83267 | 48 MPG(UK) → 39.97 MPG(US) |
| MPG (US) | L/100km | km/L | MPG (UK) | Efficiency Rating |
|---|---|---|---|---|
| 15 | 15.68 | 6.4 | 18.0 | Poor (large truck/V8) |
| 20 | 11.76 | 8.5 | 24.0 | Below average |
| 25 | 9.41 | 10.6 | 30.0 | Average (mid-size car) |
| 30 | 7.84 | 12.8 | 36.0 | Good (compact car) |
| 35 | 6.72 | 14.9 | 42.0 | Good |
| 40 | 5.88 | 17.0 | 48.1 | Very good |
| 45 | 5.23 | 19.1 | 54.1 | Excellent (hybrid) |
| 50 | 4.70 | 21.3 | 60.1 | Excellent (hybrid) |
| 55 | 4.28 | 23.4 | 66.1 | Outstanding |
| 60 | 3.92 | 25.5 | 72.1 | Outstanding (PHEV/EV-range) |
The figures below reflect real-world on-road performance ranges, which typically run 10–25% worse than official manufacturer or EPA ratings due to traffic conditions, AC use, driving style, and cold-start cycles. Use these as realistic planning benchmarks rather than best-case figures.
| Vehicle Type | Typical MPG (US) | Equivalent L/100km | km/L | Annual Fuel Cost* |
|---|---|---|---|---|
| Full Electric (BEV) | 90–130 MPGe | 1.5–2.5 Le/100km | 40–65 | ~$500 |
| Plug-in Hybrid (PHEV) | 40–80 (combined) | 3.0–6.0 | 17–33 | ~$700 |
| Full Hybrid | 38–55 | 4.3–6.2 | 16–24 | ~$800 |
| Small / City Car | 32–42 | 5.6–7.4 | 13.5–17.9 | ~$1,000 |
| Compact Car | 27–35 | 6.7–8.7 | 11.5–14.9 | ~$1,200 |
| Mid-size Car | 24–30 | 7.8–9.8 | 10.2–12.8 | ~$1,400 |
| Compact SUV / Crossover | 22–30 | 7.8–10.7 | 9.3–12.8 | ~$1,550 |
| Mid-size SUV | 18–24 | 9.8–13.1 | 7.6–10.2 | ~$1,800 |
| Full-size Pickup Truck | 14–20 | 11.8–16.8 | 6.0–8.5 | ~$2,200 |
| Performance / Sports Car | 10–20 | 11.8–23.5 | 4.3–8.5 | ~$2,500+ |
*Annual cost estimate based on 15,000 km (9,320 miles) driven per year at $1.50/liter ($5.68/US gallon). Electricity cost for EVs assumed at $0.15/kWh. Actual costs vary by region, fuel price, and driving patterns.
Every liter of petrol (gasoline) burned releases approximately 2.31 kg of CO₂. Every liter of diesel releases roughly 2.68 kg. These values are determined by the carbon content of the fuels and are consistent regardless of engine type. What changes is how many liters you burn to cover a given distance — which is exactly what your L/100km figure tells you.
Multiplying L/100km by 2.31 gives grams of CO₂ per kilometer (g/km) for petrol — the same unit used in EU emissions regulations. A car using 7.0 L/100km emits approximately 162 g/km of CO₂; one using 4.5 L/100km emits 104 g/km. The EU's current CO₂ targets for new passenger cars sit at 95 g/km on average, which equates to roughly 4.1 L/100km — achievable only with hybrid or near-hybrid drivetrains.
A key insight often missed: because MPG and fuel consumption have a hyperbolic (curved) relationship, improvements at the low end of the scale save far more CO₂ than equal MPG improvements at the high end. Going from 15 MPG to 20 MPG saves approximately 3.9 L/100km and 9 kg of CO₂ per 100 km traveled. Going from 40 MPG to 50 MPG saves only 1.2 L/100km and 2.8 kg of CO₂ per 100 km. Replacing a very inefficient vehicle delivers the largest absolute environmental gain.
| Fuel Economy | L/100km | CO₂ per km (petrol) | Annual CO₂ @ 15,000 km |
|---|---|---|---|
| 20 MPG (US) | 11.76 | 272 g/km | 4,076 kg |
| 25 MPG (US) | 9.41 | 217 g/km | 3,261 kg |
| 30 MPG (US) | 7.84 | 181 g/km | 2,718 kg |
| 40 MPG (US) | 5.88 | 136 g/km | 2,038 kg |
| 50 MPG (US) | 4.70 | 109 g/km | 1,631 kg |
| 60 MPG (US) | 3.92 | 91 g/km | 1,359 kg |
Most drivers can realistically improve their on-road fuel economy by 10–20% without replacing their vehicle. The following are the most impactful changes, ranked roughly by how much difference they make in practice.
Aggressive acceleration is the single largest source of excess fuel consumption for the average driver. Every hard launch from a traffic light converts fuel directly into heat and noise rather than forward motion. Smooth, gradual acceleration that matches the flow of traffic — rather than racing to the next red light — consistently delivers measurable improvements. Anticipating traffic ahead so you can coast to a natural stop, rather than braking hard at the last moment, also helps significantly because it preserves the kinetic energy you built up by burning fuel in the first place.
Speed matters as well. Aerodynamic drag increases with the square of velocity, meaning the engine must work disproportionately harder at higher speeds. Driving at 110 km/h instead of 130 km/h on a motorway typically reduces fuel consumption by 15–20% on that stretch. Using cruise control on open roads maintains a steadier speed than most drivers achieve manually and further reduces consumption.
Under-inflated tires increase rolling resistance — the friction the engine must overcome just to keep the vehicle moving. Studies have found that for each 10 PSI drop below the recommended inflation, fuel economy falls by roughly 0.2%. Most drivers run tires 8–12 PSI low without realizing it, producing a cumulative 1–2% penalty. Check pressure monthly when tires are cold, using the figure on the driver's door jamb sticker (not the maximum pressure printed on the tire sidewall).
Clogged air filters restrict airflow to the engine, forcing it to work harder. Worn spark plugs cause occasional misfires that waste fuel without contributing to combustion. Using an engine oil with viscosity higher than recommended increases internal friction. Regular servicing at manufacturer-recommended intervals — air filter, spark plugs, fuel filter, oil and filter — keeps the engine running at its designed efficiency. Modern engines with direct injection are particularly sensitive to dirty fuel injectors, which can reduce efficiency by 5–10% before causing any noticeable drivability symptoms.
Every extra 45 kg (100 lb) carried in the vehicle reduces fuel economy by approximately 1–2%. Remove heavy items from the boot when they are not needed. Roof-mounted cargo carriers and roof boxes increase aerodynamic drag significantly — an empty roof box can reduce motorway fuel economy by 10–25% depending on vehicle shape. Remove external accessories when not in active use.
The AC compressor can demand 3–5 kW of engine power in hot conditions. For a small city car at low speeds — already working inefficiently in stop-and-go traffic — this can worsen fuel consumption by 20–25%. At steady highway speeds, the proportional impact is smaller (5–10%), and at speeds above about 80 km/h, using the AC is actually more efficient than opening the windows, because open windows at speed create aerodynamic drag that costs more fuel than the AC compressor.
The fuel efficiency unit you encounter depends entirely on where in the world the vehicle was tested and sold. Here is a quick-reference guide to the major markets.
It is a matter of historical measurement convention. The US uses miles and gallons (imperial system), so miles per gallon is a natural expression of fuel economy. Continental Europe adopted the metric system, making liters per 100 kilometers the logical standard. They describe the same thing from opposite directions: MPG measures how far you go per unit of fuel (higher is better), while L/100km measures how much fuel you use per fixed distance (lower is better). The two cannot be compared by simple multiplication — a conversion formula involving the constant 235.215 is required.
Context is everything. For a full-size pickup truck or body-on-frame SUV, 25 MPG (9.4 L/100km) is genuinely impressive — most of these vehicles average 16–20 MPG. For a mid-size crossover, 25 MPG is average. For a compact city car, 25 MPG is below average, since cars in that segment routinely achieve 32–40 MPG. Always compare fuel economy figures within the same vehicle category and powertrain type for a fair assessment. Hybrid and electric benchmarks exist in their own separate efficiency tier.
The US gallon (3.785 liters) and the UK imperial gallon (4.546 liters) are different volumes — the UK gallon is approximately 20% larger. Because MPG measures distance traveled per gallon, using a larger gallon produces a proportionally higher MPG figure for the same journey. A vehicle achieving 40 MPG (UK) in a British road test is equivalent to about 33.3 MPG (US) — or 7.1 L/100km. This difference catches many international car shoppers off guard. Always confirm which gallon a review or specification sheet is referencing.
The main factors, roughly in order of impact: driving style (smooth acceleration and anticipating traffic flow can improve economy by 5–15%); vehicle speed (aerodynamic drag rises sharply above 100 km/h); tire pressure (under-inflation adds rolling resistance and costs 1–3%); air conditioning use (can add 0.5–1.5 L/100km); vehicle maintenance (dirty air filters, worn spark plugs, wrong-viscosity oil); cargo weight (every 45 kg costs roughly 1–2%); road type (city driving with frequent stops is far less efficient than steady highway cruising for non-hybrid vehicles); weather (cold engines run rich for several minutes after a cold start, wasting fuel); and vehicle aerodynamics (roof boxes and open windows at speed increase drag significantly).
Fill your tank completely and reset the trip odometer to zero. Drive normally — in mixed traffic, on your usual routes — until you need to refuel. Fill the tank to the same level (full), noting the exact number of liters added and reading the odometer distance since the last fill. Then: L/100km = (liters added ÷ kilometers driven) × 100. For MPG: MPG = miles driven ÷ US gallons added. For example: if you drove 420 km and filled 34 liters, your real-world consumption is (34 ÷ 420) × 100 = 8.1 L/100km. Repeating this calculation over three or four fill-ups and averaging the results gives an accurate picture of your vehicle's actual performance.
Official fuel economy figures are produced under standardized laboratory conditions: a fixed ambient temperature, no wind, no air conditioning, a specific driving cycle with set acceleration and deceleration rates, and a fully warm engine. None of these conditions fully reflect everyday driving. Real-world variables — stop-and-go traffic, hills, cold engine starts, AC use, higher motorway speeds, cargo weight, tire pressure, and individual driving habits — typically push actual consumption 10–25% above official figures. The EU's WLTP cycle, introduced in 2017, is more realistic than its predecessor NEDC and tends to run 10–15% above NEDC for the same car. The US EPA figures fall somewhere between old NEDC and WLTP in real-world accuracy.
MPGe (miles per gallon equivalent) is the US EPA's unit for rating the energy efficiency of electric and plug-in hybrid vehicles. It is based on the equivalence that 1 US gallon of petrol contains approximately 33.7 kWh of energy. The EPA calculates how many miles a vehicle can travel on 33.7 kWh of electricity and expresses that as MPGe. A modern electric car typically achieves 100–130 MPGe — far exceeding any petrol vehicle — because electric motors convert about 90% of their energy input into motion, versus 20–35% for internal combustion engines. Note that MPGe measures energy use, not carbon emissions; the carbon intensity of MPGe depends entirely on the electricity grid's fuel mix.
Diesel typically shows better L/100km figures because diesel has approximately 10–15% more energy per liter than petrol, allowing the engine to travel further on each liter. However, diesel also produces more CO₂ per liter burned (approximately 2.68 kg vs 2.31 kg for petrol). The two effects roughly cancel out, making diesel and petrol vehicles produce similar CO₂ per kilometer when properly matched. Diesel engines also emit more nitrogen oxides (NOₓ) and particulate matter without advanced exhaust after-treatment, which is why many European city centers have introduced low-emission zones that restrict older diesel vehicles.