Gas Mileage Calculator
Adjust the inputs below. Results update as you type.
How it works
MPG = miles driven / gallons used. Miles driven = current odometer − last fill-up odometer. Record both values at every fill-up for accuracy. L/100km = (liters used / km driven) × 100—note this is inverse to MPG (lower is better). Fuel economy varies 20–30% between city and highway driving. Monitor trends to catch engine or tire issues early.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Fuel economy = distance ÷ fuel used. Miles per gallon = miles driven ÷ gallons; liters per 100 km = liters ÷ (km ÷ 100).
Worked example
Driving 360 miles on 12 gallons gives 360 ÷ 12 = 30 mpg.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
How do I calculate my MPG?+
Fill the tank, reset the trip meter, drive, refill, then divide the miles driven by the gallons it took to refill.
What lowers fuel economy?+
City driving, cold weather, underinflated tires, roof racks, aggressive acceleration, and high speeds all reduce miles per gallon.
How do I convert MPG to L/100km?+
Divide 235.2 by the MPG figure. 30 mpg is about 7.8 L/100km.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.