Enter the miles you drove and the gallons it took to refill the tank, and get your
real-world fuel economy in MPG, L/100km, and km/L. Add the price per gallon to
also see your cost per mile. The math is simple —
miles ÷ gallons — but the fill-up method gives you
the most honest number your car actually delivers.
MPG from any fill-up·L/100km & km/L conversions·Optional cost per mile
How to get an accurate reading
Fill the tank completely, reset your trip odometer, drive your usual mix of roads,
then fill up completely again. Enter the miles from the trip odometer and the gallons
from the pump display. One full tank is enough for a decent estimate; averaging two
or three consecutive fills gives a more stable long-term figure. Conversions between
MPG and L/100km are exact; all reference values on this page are approximate.
Enter the miles you drove and the gallons used. Optionally add the gas price to see cost per mile. Results update as you type.
From your trip odometer between two complete fill-ups.
The amount shown on the pump when you refilled the tank.
Leave blank to skip cost per mile.
Miles per gallon (MPG)
Liters per 100 km (L/100km)
Kilometers per liter (km/L)
Cost per mile
The math, honestly
How MPG and its conversions are figured
MPG is the simplest calculation here:
MPG = miles ÷ gallons. Drive 300 miles and use 12 gallons, and
your fuel economy is 300 ÷ 12 = 25.0 MPG. Higher is better
— it means you travel farther on each gallon.
L/100km is the metric equivalent, but it runs in the opposite
direction (lower is better, since it counts fuel consumed per distance). The
conversion is L/100km = 235.215 ÷ MPG. At 25.0 MPG that's
235.215 ÷ 25.0 ≈ 9.41 L/100km. The constant 235.215
comes from the unit conversion between miles, gallons, and liters.
km/L is a third way to express the same thing, common in Asia
and Latin America. It's directly proportional to MPG:
km/L = MPG × 0.425144. At 25.0 MPG that's
25.0 × 0.425144 ≈ 10.63 km/L.
Cost per mile (when you enter a gas price) is
price ÷ MPG. At $3.50/gal and 25.0 MPG, each mile costs
3.50 ÷ 25.0 = $0.14. This covers fuel only — not
depreciation, insurance, or maintenance.
Typical MPG by vehicle type
Approximate real-world combined fuel economy for common vehicle categories, based
on typical EPA ratings and observed on-road averages. Use these as a sanity check
on your result — not as a target. All values are approximate.
Vehicle type
Approx. MPGcombined, real-world
L/100kmapproximate
Example
Compact sedan
30–38
6.2–7.8
Honda Civic, Toyota Corolla
Midsize sedan
26–34
6.9–9.1
Toyota Camry, Honda Accord
Compact SUV
25–32
7.4–9.4
Toyota RAV4, Honda CR-V
Midsize SUV
20–27
8.7–11.8
Ford Explorer, Jeep Grand Cherokee
Full-size truck
16–22
10.7–14.7
Ford F-150, Chevy Silverado
Hybrid sedan
42–56
4.2–5.6
Toyota Prius, Honda Insight
Approximate figures for illustration. Real-world MPG varies with driving style,
speed, terrain, weather, and vehicle condition. Check your car's EPA window sticker
or fueleconomy.gov for model-specific ratings.
Reading the result
A single MPG number hides a lot of variation. Here's what it actually tells you
and where to be skeptical.
One tank is a data point, not a verdict
A single fill-up captures one slice of your driving — that particular mix of highway, city, temperature, and load. A short tank with lots of cold starts will look worse than a long highway cruise. Average two or three consecutive fills for a more stable read on your car's real habits.
Fill technique matters
Topping off (clicking the trigger after the auto-shutoff) adds inconsistent amounts of fuel and throws off the gallons figure. Stop at the first click, both at the start and end of your measurement interval, for the cleanest number.
Compare MPG to your own baseline, not the sticker
The EPA window-sticker number is a controlled-lab measurement. Your real-world average will almost always be a bit lower, and that's normal. What matters is whether your number is stable over time — a sudden drop of 2–3 MPG can signal a maintenance issue (low tire pressure, dirty air filter, aging spark plugs).
L/100km and km/L are exact conversions, not estimates
The L/100km and km/L figures in the result are mathematically exact from your MPG — 235.215 ÷ MPG and MPG × 0.425144 respectively. They're labeled approximate only when referring to the reference table above, which uses rounded vehicle-type averages.
MPG glossary
The terms behind the calculator, in plain English.
MPG (miles per gallon)
How far your car travels on one gallon of fuel — the US measure of fuel efficiency, where higher is better. Calculated as miles driven divided by gallons used. Your car's trip computer shows a running average; the fill-up method gives you the measured truth.
L/100km (liters per 100 kilometers)
The metric measure of fuel consumption — how many liters it takes to drive 100 km, where lower is better. It's the inverse of MPG: it counts fuel per distance rather than distance per fuel. The conversion is 235.215 ÷ MPG.
km/L (kilometers per liter)
A metric efficiency measure common in Asia and Latin America, analogous to MPG but in metric units: distance per unit of fuel, where higher is better. Converts from MPG with MPG × 0.425144.
Fill-up method
The most accurate way to measure real-world fuel economy: fill completely, reset the trip odometer, drive, fill completely again, then divide the miles by the gallons pumped. It bypasses the trip computer and measures what actually went into and out of the tank.
Cost per mile (fuel only)
The fuel cost of driving one mile: gas price divided by MPG. At $3.50/gal and 25 MPG, each mile costs $0.14 in fuel. Useful for estimating reimbursement or comparing cars. Does not include depreciation, insurance, or maintenance.
Combined MPG
The EPA's blended figure: 55% city driving and 45% highway driving by distance. It's the number on the window sticker and the standard comparison point. Real-world combined depends on your actual driving mix — mostly highway use will beat the combined rating; heavy city use will trail it.
Frequently asked
Divide the miles you drove by the gallons it took to refill the tank:
MPG = miles ÷ gallons. If you drove 300 miles and needed 12 gallons, your fuel economy is 25.0 MPG. For the most accurate result, fill up completely, reset your trip odometer, drive your usual routes, then fill up completely again and use those two numbers.
It depends on vehicle type. A compact sedan averaging 30–35 MPG is doing well; a hybrid above 45 MPG is excellent. For a non-hybrid gas car, anything above 30 MPG combined is generally considered good. The reference table above shows approximate ranges by category. More important than hitting a target is knowing your baseline and watching for drops over time — a sudden fall of 2–3 MPG can indicate a maintenance issue.
Divide 235.215 by the MPG figure: L/100km = 235.215 ÷ MPG. For example, 25 MPG ÷ 235.215 gives 9.41 L/100km. Going the other way, MPG = 235.215 ÷ L/100km. Note they move in opposite directions — higher MPG means lower L/100km — because one measures distance-per-fuel and the other measures fuel-per-distance. The calculator shows both automatically.
EPA ratings are measured on a laboratory dynamometer using a standardized drive cycle under controlled temperature and load. Real-world driving differs in important ways: highway speeds above 60 mph increase aerodynamic drag significantly, cold weather thickens engine oil and increases warm-up fuel use, air conditioning adds engine load, and aggressive acceleration wastes energy. Most drivers see real-world combined economy 5–15% below the EPA figure, with the gap widest in extreme weather or stop-and-go city traffic.
Modern trip computers are usually accurate within 1–3%, but some brands read optimistically by up to 8%. The fill-up method is the ground-truth approach — the pump meter measures gallons and your odometer measures miles. For a stable long-term average, calculate from at least two or three consecutive full-tank intervals. Partial fills and inconsistent fill technique (topping off vs. stopping at first click) are the main sources of error in the fill-up method.
Cost per mile (fuel only) is gas price divided by MPG: at $3.50/gal and 25 MPG, each mile costs 3.50 ÷ 25 = $0.14. It's useful for comparing running costs between vehicles or estimating mileage reimbursement. Enter the gas price in the calculator above and it appears automatically. Note this covers fuel only; the IRS standard mileage rate includes depreciation, maintenance, and insurance as well.
Common mistakes
MPG calculations from fill-ups are accurate only when the fuel and mileage measurements are taken consistently — small procedural errors compound into meaningful errors in the result.
Measuring from a partial fill to another partial fill
MPG = miles driven ÷ gallons used, and gallons used is accurately known only when both fill-ups are to the same level. Filling to the first click at one stop and topping off at the next means gallons added at the second fill does not reflect actual consumption over that interval. The standard method is to fill to the first automatic shutoff at both start and end and record the trip odometer at each stop.
Mixing miles and kilometers, or gallons and liters, without converting
Odometers in Canada and Europe read in kilometers; fuel is sold in liters. Dividing kilometers by gallons produces a number that looks like MPG but is actually km/gal — roughly 60% of the correct MPG figure. Convert first: 1 mile = 1.60934 km; 1 US gallon = 3.78541 liters. For L/100km (the metric standard), the formula is liters ÷ (kilometers ÷ 100).
Using a single fill-up to draw conclusions about fuel economy
One fill-up interval reflects the driving conditions of that specific tank: highway versus city mix, temperature, load, and fuel grade all vary. A single data point is not representative. EPA estimates are based on standardized multi-run lab protocols precisely because single measurements are unreliable. Track three to five consecutive fill-ups and average the results for a meaningful personal MPG baseline.