Mpg Calculator

Calculate your car's actual fuel economy from the pump. Enter the miles you drove and the gallons it took to refill, or log several fill-ups to see your average MPG, cost per mile and the metric equivalents.

How to calculate MPG

Miles per gallon is simply the distance driven divided by the fuel used: MPG = miles ÷ gallons. The most reliable way to measure it is the fill-to-fill method, because the fuel gauge is not precise enough.

1. Fill the tank until the pump clicks off, and note the odometer or reset the trip meter.
2. Drive normally until you need fuel again.
3. Fill the tank until it clicks off again, and note the gallons dispensed.
4. Divide the miles driven since the last fill-up by those gallons.

Use the same pump behaviour each time — stop at the first click rather than topping off — so each fill is equally full.

Worked example

You filled up at 41,200 miles and again at 41,512 miles, when the pump took 11.2 gallons. You drove 312 miles, so your fuel economy for that tank was 312 ÷ 11.2 = 27.9 MPG. At $3.39 a gallon, the tank cost $37.97, which is about 12.2 cents per mile, or $12.17 per 100 miles.

Why average several fill-ups

A single tank can be skewed by one long highway trip, a week of short cold-weather drives, or a slightly different click-off point at the pump. Averaging over several tanks smooths this out. The correct way is to add up all the miles and all the gallons and divide — not to average the individual MPG figures, which gives too much weight to short tanks. The multi-fill calculator above does it the right way.

MPG, L/100 km and km/L

L/100 km is a consumption figure — how much fuel for a fixed distance — rather than economy, which is why lower is better. It makes savings easier to compare: going from 10 to 8 L/100 km saves exactly 2 litres every 100 km.

Why your MPG differs from the sticker

• Driving style: hard acceleration and braking use more fuel.
• Speed: aerodynamic drag rises quickly above about 50 mph.
• Trip length: engines are least efficient when cold, so short trips lower MPG.
• Weather: cold air, winter fuel blends and heater or A/C use all reduce economy.
• Load and roof racks: weight and drag add up.
• Tyre pressure and maintenance: under-inflated tyres and dragging brakes cost fuel.

Tracking fuel economy over time

A sudden drop in MPG with no change in driving can be an early warning of a problem: low tyre pressure, a sticking brake, a failing oxygen sensor or a thermostat stuck open. Logging every fill-up — date, odometer, gallons and price — makes such changes visible and also gives you an accurate record of fuel costs for budgeting or mileage claims. The paid workbook keeps this log and charts your MPG automatically.

Cost per mile and budgeting

Fuel cost per mile is the number that matters for budgets and comparing cars: at 28 MPG and $3.40 a gallon, fuel costs about 12 cents a mile; at 45 MPG it is 7.6 cents. Multiply by your annual mileage to see the yearly difference. Remember that fuel is only part of the cost of driving; insurance, maintenance, tyres and depreciation often add more per mile than fuel does.

Improving your MPG

Small habits add up. Accelerate smoothly and anticipate stops so you brake less; keep highway speeds moderate, because fuel use rises quickly above about 60 mph in most cars; check tyre pressure monthly against the placard in the door jamb; remove roof racks and heavy items you are not using; and combine errands into one trip so the engine spends more time warm. Logging your fill-ups before and after a change is the best way to see what works for your own car.

Electric and hybrid equivalents

Hybrids are measured in MPG like petrol cars, and the fill-to-fill method works the same way. Plug-in hybrids are harder to measure because some miles come from the battery; track the electricity separately for a true picture. Fully electric vehicles use miles per kWh or kWh per 100 miles, and the EPA publishes an MPGe (miles per gallon equivalent) figure based on 33.7 kWh being equivalent to one gallon of gasoline, which lets you compare efficiency across fuel types.