Work out your real gas mileage from a fill-up, plus cost per mile and yearly fuel cost
| MPG | L/100km | Fuel Cost per 1,000 Miles | Annual Fuel Cost |
|---|---|---|---|
| 15 | 15.7 | $233.33 | $2,800 |
| 20 | 11.8 | $175.00 | $2,100 |
| 25 | 9.4 | $140.00 | $1,680 |
| 30 | 7.8 | $116.67 | $1,400 |
| 40 | 5.9 | $87.50 | $1,050 |
| 50 | 4.7 | $70.00 | $840 |
Notice the savings shrink as you climb: going 15→20 mpg saves $700 a year, but 40→50 mpg saves only $210. The gallons-per-mile view (right there in the L/100km column) is what makes that obvious, which is why most of the world reports it instead of mpg.
| Vehicle Class | Typical Combined MPG | Annual Fuel at 12k mi, $3.50 |
|---|---|---|
| Compact car | 30 – 36 | $1,167 – $1,400 |
| Midsize car | 26 – 34 | $1,235 – $1,615 |
| Midsize hybrid | 45 – 58 | $724 – $933 |
| Compact SUV | 24 – 30 | $1,400 – $1,750 |
| Three-row SUV | 19 – 24 | $1,750 – $2,211 |
| Half-ton pickup | 17 – 24 | $1,750 – $2,470 |
| Battery EV (MPGe basis) | 100 – 130 | compare at your electric rate |
Ranges reflect recent-model combined EPA figures across popular trims; individual trims vary. Annual figures come straight from the mpg math at $3.50 a gallon.
Your car's dashboard MPG readout is an estimate, and it's usually optimistic by a few percent. The pump tells the truth. This calculator uses the full-to-full method, the same procedure Edmunds and Consumer Reports describe: fill the tank completely, reset the trip odometer, drive until the next fill, then divide miles by however many gallons the second fill took.
MPG = miles driven ÷ gallons used. Cost per mile = price per gallon ÷ MPG. Annual fuel cost = annual miles ÷ MPG × price. For the metric column, L/100km = 235.215 ÷ MPG, a constant built from 3.785 liters per gallon and 1.609 kilometers per mile.
After your next fill-up, type the trip-odometer miles and the gallons from the pump receipt, plus what you paid per gallon. Add your typical annual miles if you want the yearly projection. One tank is a snapshot; three tanks averaged is a real number, since pump shutoff points and driving mix wobble single measurements.
Between fills you cover 312 miles, and the pump takes 11.9 gallons at $3.45. Your MPG is 312 ÷ 11.9 = 26.2. That's 235.215 ÷ 26.2 = 8.97 L/100km for anyone reading a metric spec sheet, and the fill-up cost 11.9 × $3.45 = $41.06. Per mile, fuel runs $3.45 ÷ 26.2 = 13.2 cents. Over a 13,500-mile year, the car drinks 13,500 ÷ 26.2 = 514.9 gallons, which bills out at $1,776.42.
That annual figure is the one worth staring at. A driver moving from a 20 mpg truck to this 26.2 mpg car saves 4.1 cents a mile, about $552 a year at 13,500 miles. Plug your own two cars into the calculator and the trade becomes concrete instead of vibes.
Fill the tank, reset the trip odometer, drive normally, then refill and note the gallons it took. MPG is miles on the trip odometer divided by gallons to refill. 312 miles on 11.9 gallons is 26.2 mpg. For a reliable number, average three or more fill-ups, since single tanks vary with driving mix and pump shutoff.
Divide 235.215 by the MPG figure. A 26.2 mpg car burns 235.215 ÷ 26.2 = 8.98 L/100km. The constant comes from converting gallons to liters (3.785) and miles to kilometers (1.609). Note the scale inverts: a lower L/100km number is better, and doubling efficiency cuts L/100km in half but does not double mpg savings linearly.
For a gasoline vehicle, anything above 30 mpg combined is solid for a modern car, 40-plus is excellent, and hybrids run 45 to 58. Full-size pickups sit around 17 to 24 combined, three-row SUVs around 19 to 24. At $3.50 a gallon and 12,000 miles a year, moving from a 20 mpg truck to a 30 mpg sedan saves $700 a year.
EPA figures come from lab tests on a dynamometer; your number reflects your right foot, your climate, and your cargo. Cold weather alone can knock 10% to 20% off winter mileage because engines run richer and take longer to warm up. Highway driving usually beats the city figure, and speed above 60 mph drags mileage down as aerodynamic drag climbs.
Cheap wins first: keep tires at the placard pressure (underinflation costs roughly 0.2% per psi), drop highway speed toward 65, take the roof rack off when unused, and replace a clogged air filter on an older engine. Combined, sensible habits and maintenance are commonly worth 5% to 10%, which on a 25 mpg car at $3.50 is about $150 a year at 12,000 miles.