Calculator guide
Calculate vehicle fuel economy from miles driven and gallons consumed, with a gallons-per-100-miles comparison.
Formula or method
MPG = miles driven ÷ gallons used; gallons per 100 miles = gallons used ÷ miles × 100.
How to use this calculator
- Enter the miles driven between fill-ups.
- Enter gallons used for that distance.
- Review MPG and the inverse consumption measure; use consistent units and a full-tank interval.
Worked example
Driving 350 miles on 12 gallons gives 350/12 = 29.17 MPG and about 3.43 gallons per 100 miles.
Understanding the result
Higher MPG means fewer gallons per mile, but MPG savings are not linear: improving from 10 to 15 MPG saves more fuel than 30 to 35 MPG over the same distance.
Limitations and assumptions
- The estimate depends on accurate distance and fuel measurements.
- It does not adjust for terrain, traffic, temperature, tire pressure, or fuel blend.
Frequently asked questions
Why use gallons per 100 miles too?
It expresses fuel consumed directly and makes comparisons between vehicles easier.
Should I use the dashboard MPG?
A full-tank calculation from receipts can provide an independent check.
Can I enter kilometers and liters?
This calculator's output is labeled MPG; convert units before entering them.
Sources
Educational information only; verify important decisions with a qualified professional.