Article — Fuel Consumption Calculator
Fuel Consumption Calculator — Full Guide
Fuel consumption is the amount of fuel a vehicle burns over a set distance, reported as liters per 100 kilometers (L/100km) in most of the world and as miles per gallon (MPG) in the US. The formula is simple: divide fuel used by distance, then scale. A 7 L/100km figure equals about 33.6 MPG, and that vehicle will burn 35 liters on a 500-kilometer trip.
What makes fuel consumption interesting is everything around the number. The same engine produces different real-world results depending on driving style, weather, terrain, and tire pressure. The EPA assigns a single combined figure on every new-car window sticker, but actual mileage typically lands 10 to 25% lower in normal use.
What is fuel consumption?
Fuel consumption is the ratio of fuel burned to distance traveled. Three reporting units dominate: L/100km (Europe, most of the world), MPG (US, UK informally), and km/L (Japan, Korea, parts of Latin America). The first puts fuel in the numerator and distance in the denominator; the others invert that. The arithmetic is identical, but the intuition flips: lower L/100km is better, higher MPG is better.
Standardized testing matters because lab and road numbers diverge. The EPA's Federal Test Procedure runs vehicles on a dynamometer through fixed urban, highway, and combined cycles. Europe uses WLTP (Worldwide Harmonized Light Vehicles Test Procedure). Both adjust raw lab figures downward to better match street driving, but neither captures cold starts, aggressive acceleration, or roof-rack drag — the kind of things that move real fuel consumption by 15% or more.
The fuel consumption formula
The math is one line. For L/100km, multiply fuel used in liters by 100, then divide by kilometers driven. For MPG, divide miles by US gallons. For km/L, divide kilometers by liters.
L/100km = (L × 100) ÷ km MPG = mi ÷ galkm/L = km ÷ L L/100km = 235.215 ÷ MPGTrip cost = L × $/L CO₂ kg = L × 2.31The MPG-to-L/100km factor of 235.215 comes from 100 multiplied by 3.78541 (L per US gallon) divided by 1.60934 (km per mile). The relationship is reciprocal, not linear. Doubling MPG only halves L/100km at low values; at high values the reduction is larger in absolute terms but smaller in percentage. That is why pushing a 50 MPG car to 60 MPG saves less fuel than pushing a 15 MPG truck to 18 MPG.
Why MPG and fuel consumption work in opposite directions
MPG measures distance per unit of fuel. L/100km measures fuel per unit of distance. The two are reciprocals, which is why their intuition runs opposite ways. The European unit better reflects what consumers actually want to know — "how much fuel will this car burn?" — while the US unit better reflects "how far can I get on this tank?".
The reciprocal effect has a counterintuitive consequence. Going from 10 to 20 MPG saves about 500 gallons per 10,000 miles. Going from 30 to 40 MPG saves only 83 gallons over the same distance. The biggest fuel savings come from improving inefficient vehicles, not pushing efficient ones higher.
What good fuel consumption looks like
Benchmarks shift with vehicle class. A compact sedan averages 6 to 7 L/100km (33 to 40 MPG combined) in EPA testing. A midsize SUV runs 8 to 10 L/100km (24 to 30 MPG). A full-size pickup truck typically lands 11 to 14 L/100km (17 to 22 MPG). Hybrids cut those figures by 30 to 40%, and pure battery EVs use the gasoline-equivalent MPGe scale instead.
- Compact sedan 32-38 MPG combined, 6.2-7.4 L/100km
- Midsize sedan 28-34 MPG, 6.9-8.4 L/100km
- Compact SUV 26-30 MPG, 7.8-9.0 L/100km
- Full-size SUV 17-22 MPG, 10.7-13.8 L/100km
- Pickup truck 17-23 MPG, 10.2-13.8 L/100km
- Hybrid sedan 45-55 MPG, 4.3-5.2 L/100km
- BEV compact 110-140 MPGe
Factors that affect fuel consumption
Driving style is the biggest lever. The EPA estimates aggressive driving — hard acceleration, hard braking, sustained high speed — cuts MPG by 15 to 30% on the highway and up to 40% in city traffic. The 75 mph versus 65 mph difference alone shifts highway MPG by 12 to 15%.
After driving style, the major factors are aerodynamics, weight, accessory loads, and tire pressure. A roof box can add 25% to highway fuel use. Each 100 pounds of cargo cuts MPG by about 1%. Underinflated tires shave 3 to 5%. Cold weather is the seasonal wildcard: gasoline engines lose 12 to 25% of fuel economy in freezing temperatures, and hybrids and EVs lose even more.
Trip computers often report 3 to 8% optimistic fuel consumption versus actual fill-up math. For a true reading, fill the tank, reset the odometer, drive the trip, refill to the same brim, and compute fuel used divided by distance. Repeat over 3 to 5 tanks for a reliable average.
Fuel consumption and CO₂ emissions
Burning gasoline produces 2.31 kg of CO₂ per liter, according to the US EPA and EIA. A US gallon yields 8.887 kg. The CO₂ mass is greater than the fuel mass because oxygen from the air combines with carbon during combustion. Diesel produces slightly more — about 2.68 kg per liter — because diesel is denser and contains more carbon per liter.
For a typical passenger vehicle driving 12,000 miles a year at 24.2 MPG combined, the EPA puts annual CO₂ emissions at 4.6 metric tons. Cutting fuel consumption by 20% — through driving habits, tire pressure, weight reduction — eliminates roughly 920 kg of CO₂ per car per year.
Tips for improving fuel consumption
Slow down. The biggest single factor for highway driving is sustained speed: dropping from 75 to 65 mph can improve highway MPG by 12 to 15%. Maintain tire pressure to the door-jamb spec; underinflation by 5 psi costs 1 to 2 MPG. Remove roof racks and cargo boxes when they are not needed. Avoid extended idling (modern engines waste fuel idling more than they save by skipping a restart). Smooth acceleration and braking are the cheapest fuel-saving habits available.
Use cruise control on flat highway stretches. It holds a steady throttle position and avoids the small acceleration spikes that drivers introduce unconsciously. EPA testing puts the cruise-control benefit at 7 to 14% on long flat highway drives.
Lab versus real-world fuel consumption
EPA window-sticker numbers undercount real fuel consumption for most drivers. The lab cycles can not reproduce stop-and-go traffic, hilly terrain, aggressive starts, or 95°F days with the A/C maxed. The 2008 EPA test revision adjusted lab values downward by roughly 10% city and 22% highway, but variance remains. A vehicle rated at 30 MPG combined will typically deliver 25 to 28 MPG in mixed real-world driving.
For an accurate personal number, compute fuel consumption from fill-up math over several tanks, not from the trip computer. Use the calculator above with real distance and real fuel used. The result will tell you how the car actually performs in your conditions, not how it performed on an EPA dynamometer in Ann Arbor.