Fuel Consumption Calculator

Fuel economy is measured differently worldwide: L/100km in Europe, MPG in USA/UK.

Lower L/100km or higher MPG means better efficiency.

To find savings:

• Track your consumption
• maintain your vehicle
• drive smoothly
• compare routes

Even small improvements add up over time.

Fuel consumption in L/100km is calculated as (Fuel Used ÷ Distance) × 100, where fuel is in liters and distance is in kilometers. For example, using 40 liters over 500 km gives (40 ÷ 500) × 100 = 8 L/100km.

For imperial units, miles per gallon is MPG = Distance (miles) ÷ Fuel (gallons); driving 300 miles on 10 US gallons equals 30 MPG.

Note the two measures are inverse: L/100km rises as efficiency falls, while MPG rises as efficiency improves.

The US EPA and fueleconomy.gov publish official ratings using standardized city and highway test cycles for consistent comparison.

To convert liters per 100 kilometers to US miles per gallon, use MPG = 235.215 ÷ (L/100km). For example, 8 L/100km equals 235.215 ÷ 8 = 29.4 MPG.

For UK (imperial) gallons, use MPG = 282.481 ÷ (L/100km), since one imperial gallon (4.54609 L) is larger than one US gallon (3.78541 L).

Kilometers per liter is simply km/L = 100 ÷ (L/100km), so 8 L/100km equals 12.5 km/L.

The BIPM and NIST define these underlying SI-derived and customary units, ensuring the liter, kilometer, and mile conversions used here are internationally standardized and reproducible.

Fuel economy uses length and volume units defined under the International System of Units (SI) and customary systems. The kilometer and liter are the metric basis for L/100km and km/L, while the mile and gallon underpin MPG.

Per NIST and BIPM, the liter is 0.001 cubic meters and the international mile equals exactly 1,609.344 meters.

Critically, the US gallon (3.785411784 liters) differs from the UK imperial gallon (4.54609 liters), which is why US and UK MPG figures for the same car diverge by about 20%.

Always confirm which gallon a rating uses before comparing vehicles across markets, as mixing them produces misleading efficiency numbers.

Trip fuel cost is calculated as (Distance ÷ 100) × Consumption × Fuel Price when using metric units. For a 500 km trip at 8 L/100km with fuel at $1.50 per liter: (500 ÷ 100) × 8 × 1.50 = $60.

Cost per kilometer is total cost divided by distance, or $60 ÷ 500 = $0.12/km.

In imperial units, cost per mile = Fuel Price per gallon ÷ MPG; at $4.50 per gallon and 30 MPG, that is $0.15 per mile.

Tracking cost per distance lets you budget road trips and compare vehicles fairly, independent of tank size or fill-up frequency.

Vehicle CO2 emissions are estimated by multiplying fuel volume by a fuel-specific emission factor.

According to the US EPA, burning one liter of gasoline releases about 2.32 kg of CO2, while diesel releases roughly 2.68 kg per liter because of its higher carbon density. So using 40 liters of gasoline produces about 40 × 2.32 = 92.8 kg of CO2.

The EPA's often-cited figure of 8,887 grams of CO2 per US gallon of gasoline is the same relationship expressed in imperial units.

These factors reflect complete combustion, where each carbon atom bonds with two oxygen atoms, making CO2 heavier than the fuel burned.

Aerodynamic drag rises with the square of speed, so the power needed to overcome it climbs sharply at higher velocities.

HyperPhysics (Georgia State University) expresses drag force as F = ½ρv²C(d)A, where:

• ρ is air density
• v is speed
• C(d) is the drag coefficient
• A is frontal area

Doubling speed roughly quadruples drag force, which is why highway cruising at very high speeds burns disproportionately more fuel. This is also why aerodynamic shaping, removing roof racks, and closing windows at speed improve efficiency.

At low city speeds, rolling resistance and repeated acceleration dominate instead, explaining why stop-and-go driving is often less efficient than steady highway travel.

Fuel consumption calculations serve drivers, fleet managers, and policymakers alike.

Individuals use them to budget road trips, compare a prospective car's running costs, and verify whether a fuel-saving habit actually works. Logistics and delivery fleets rely on L/100km and cost-per-mile figures to schedule routes, negotiate fuel budgets, and cut operating expenses across hundreds of vehicles.

Regulators such as the US EPA and the European Environment Agency use standardized economy and CO2 data to set emission targets and label new cars.

Encyclopaedia Britannica notes that fuel economy standards have driven major engineering gains since the 1970s, making accurate per-vehicle measurement essential for both personal savings and climate accounting.

Several common mistakes distort fuel consumption results:

• The most frequent error is mixing US and UK gallons, which inflates or deflates MPG by about 20% and makes vehicle comparisons meaningless.
• Another common mistake is confusing the direction of the two metrics: lower L/100km is better, but higher MPG is better, so they cannot be added or averaged interchangeably.
• Drivers also over-rely on a single tank when the pump auto-shutoff varies fill levels; averaging several full-to-full fill-ups gives far more reliable results.
• Finally, ignoring conditions such as cold starts, cargo weight, or air conditioning skews numbers.

Khan Academy emphasizes consistent units throughout any calculation, so always confirm liters versus gallons and kilometers versus miles before dividing.

Maximum driving range is estimated as Range = (Tank Capacity ÷ Consumption) × 100 in metric units. With a 50-liter tank and consumption of 8 L/100km, range is (50 ÷ 8) × 100 = 625 km.

In imperial terms, Range = Tank Capacity (gallons) × MPG; a 13-gallon tank at 30 MPG yields 390 miles.

Real-world range is typically lower than this ideal because manufacturers reserve a buffer, and consumption worsens with cold weather, hills, headwinds, and heavy loads.

For safety, plan refueling around 80% of the calculated range rather than running the tank to empty, especially on long or remote routes.