Fuel Economy Converter: MPG to L/100km, km/L
Convert between MPG (US), MPG (UK), L/100km, and km/L. Fuel economy uses non-linear math because MPG and L/100km are inverse measures (higher MPG is better, lower L/100km is better). The calculator handles the math correctly and lets you compare car efficiency across measurement systems.
Fuel economy uses a non-linear conversion because MPG and L/100km are inverse measures: higher MPG is better, lower L/100km is better. The calculator handles this automatically.
Fuel economy reference table
Common figures across all four unit systems.
| MPG (US) | MPG (UK) | L/100km | km/L |
|---|---|---|---|
| 15 | 18 | 15.7 | 6.4 |
| 20 | 24 | 11.8 | 8.5 |
| 25 | 30 | 9.4 | 10.6 |
| 30 | 36 | 7.84 | 12.75 |
| 35 | 42 | 6.72 | 14.88 |
| 40 | 48 | 5.88 | 17 |
| 50 | 60 | 4.7 | 21.3 |
| 60 | 72 | 3.92 | 25.5 |
| 80 | 96 | 2.94 | 34 |
| 100 | 120 | 2.35 | 42.5 |
About fuel economy
Why MPG and L/100km move oppositely
MPG measures distance per unit fuel (miles per gallon), so higher is better. L/100km measures fuel per unit distance (liters per 100 kilometers), so lower is better. They are mathematical inverses. The conversion is non-linear: doubling MPG halves L/100km, but the percentage improvement gets smaller as MPG rises. Going from 20 MPG to 25 MPG saves much more fuel per mile than going from 50 MPG to 55 MPG.
US MPG vs UK MPG
The US gallon is 3.785 liters; the UK (imperial) gallon is 4.546 liters, about 20 percent larger. So 30 MPG in the US equals 36 MPG in the UK for the same actual fuel consumption. When comparing car reviews from the US and UK, always check which gallon is meant. Most modern UK reviews now use L/100km or MPG-UK; older reviews may not specify.
Why L/100km is the better measure
Because fuel cost is what you actually pay for, and fuel cost scales linearly with L/100km but not with MPG. If you halve your fuel use, you halve your fuel bill: 10 L/100km to 5 L/100km gives 50 percent savings. Going from 23 MPG (10 L/100km) to 47 MPG (5 L/100km) is the same 50 percent saving in fuel and money, but the MPG jump looks much bigger than it is.
Typical fuel economy figures
Modern small petrol cars: 5 to 7 L/100km (35 to 47 MPG US, 42 to 56 MPG UK). Small diesel: 4 to 5 L/100km. Hybrids: 4 to 5 L/100km. Plug-in hybrids on charge: 1 to 3 L/100km. Large SUVs and trucks: 9 to 14 L/100km. Sports cars: 9 to 18 L/100km. Pakistani-popular cars (Mehran, Cultus, Wagon-R, Mira, Alto) typically achieve 11 to 16 km/L (6 to 9 L/100km).
Real-world vs official figures
Official fuel economy ratings (EPA in the US, WLTP in Europe) come from standardized lab tests that often overstate real-world economy by 5 to 25 percent. The EPA "combined" figure is closer to real driving than the city or highway figures alone. For your specific car, calculate actual consumption: fill the tank, reset the trip meter, drive normally for a few hundred kilometers, fill up again, divide kilometers by liters added.
Speed and fuel economy
Most cars peak efficiency around 80 to 90 km/h (50 to 56 mph). Above 110 km/h, drag rises sharply and consumption climbs. At 130 km/h a typical car uses 30 percent more fuel than at 90 km/h. Driving steadily, anticipating stops, and avoiding hard acceleration can improve real-world fuel economy by 10 to 20 percent.
EV efficiency comparison
Electric vehicles are measured in kWh/100km (or MPGe in the US). A good EV is 15 kWh/100km; average is 20 kWh/100km. In the US, the EPA converts this to MPGe assuming 33.7 kWh per "gallon equivalent". For Pakistani drivers comparing a petrol car to an EV by cost, multiply L/100km by per-liter petrol cost vs kWh/100km by per-kWh electricity cost.
Diesel vs petrol economy
Diesel fuel has about 11 percent more energy per liter than petrol, so diesel L/100km figures look better than equivalent petrol cars even before accounting for engine efficiency. Diesel engines also typically achieve 20 to 30 percent better fuel efficiency. Combined, diesels often show 30 to 40 percent lower L/100km than their petrol equivalents.
Fuel cost per kilometer math
To find cost per km: (L/100km × fuel price per liter) / 100. At 7 L/100km and petrol at Rs 280/L: (7 × 280) / 100 = Rs 19.6 per km. For 1000 km driven that is Rs 19,600 in fuel. Use the calculator to convert from MPG if your reference figure is in that unit.
Divide 235.215 by the MPG (US) figure to get L/100km. So 30 MPG (US) = 235.215 / 30 = 7.84 L/100km. The relationship is inverse: higher MPG is better, lower L/100km is better. The calculator handles the math automatically.
The US gallon (3.785 L) and UK gallon (4.546 L) are different sizes. The UK gallon is about 20 percent larger. So 30 MPG (US) = 36 MPG (UK) for the same fuel consumption. The calculator handles both, but always clarify which gallon you mean when comparing cars across the Atlantic.
L/100km directly measures fuel consumed per unit of distance, which is what you actually pay for. MPG measures distance per unit of fuel, an inverse measure. The difference is significant for fuel-efficient vehicles: going from 50 MPG to 100 MPG saves much less fuel than going from 20 MPG to 25 MPG, even though the second jump is "smaller". L/100km makes this clear: 4.7 vs 2.35 saves the same fuel as 11.8 vs 9.4.
Modern small petrol cars typically achieve 5 to 7 L/100km (47 to 33 MPG US, 40 to 56 MPG UK). Small diesel cars do 4 to 5 L/100km. Hybrids achieve 4 to 5 L/100km. Plug-in hybrids 1 to 3 L/100km on average. Large SUVs and trucks: 9 to 14 L/100km. Sports cars: 9 to 18 L/100km.
Kilometers per liter, a metric MPG-equivalent. Common in India, Pakistan, Bangladesh, Japan, and parts of Southeast Asia. 1 km/L = 2.352 MPG (US). 14 km/L = 33 MPG (US). The calculator converts between km/L and all other units.
Fuel economy is non-linear: doubling MPG does not halve L/100km. The calculator converts every input to L/100km internally, then back to the requested output unit. This gives the correct result for any direction. For example, 20 MPG (US) = 11.76 L/100km. 40 MPG (US) = 5.88 L/100km. Note that doubling MPG halves the L/100km figure exactly.
Multiply your L/100km by your fuel price per liter, then divide by 100. So at 7 L/100km with petrol at Rs 280/L: (7 × 280) / 100 = Rs 19.6 per km. Use the calculator to convert your MPG figure to L/100km first if needed.
They are based on standardized lab tests and tend to overstate real-world economy by 5 to 25 percent. The EPA combined figure is closer to real driving than the highway or city figures alone. Real driving variables include speed, traffic, climate, tire pressure, and load.
EV efficiency is measured in kWh per 100km (or MPGe in the US). 15 kWh/100km is good; 20 kWh/100km is average. MPGe is a less useful measure because it converts energy units back to a notional gallon equivalent. For EV-to-petrol cost comparison, calculate kWh per km times electricity rate vs L per km times fuel rate.
Maintain steady speed (cruise control on highways), avoid hard acceleration and braking, keep tires at correct pressure, remove unnecessary weight (especially roof racks), use the recommended grade of fuel, and service the engine regularly. Speed matters too: most cars peak in efficiency around 80-90 km/h; above 110 km/h consumption rises sharply.
The conversion math is exact. The calculator does not estimate the real-world performance of a specific car; it converts between units. For your specific vehicle, use the fuel-up method: fill the tank, reset the trip meter, drive normally, fill up again, divide kilometers driven by liters added.
Diesel fuel has higher energy density per liter than petrol (about 11 percent more). So a diesel engine of similar size and efficiency will show lower L/100km than the equivalent petrol. The MPG advantage of diesel is partly real efficiency and partly the denser fuel. The calculator works equally well for either.
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