How is MPG calculated?

MPG = miles driven ÷ gallons used. Miles driven equals your current odometer minus the previous odometer reading. The more tanks you log, the more accurate your average becomes.

Why is my MPG lower than the EPA estimate?

EPA estimates are measured under controlled lab conditions. Real-world MPG is affected by traffic, speed, air conditioning, elevation, cold starts, tire pressure, and vehicle load. A 15–20% difference from the EPA figure is common.

Does this tool store my data on a server?

No. All fill-up history is saved exclusively in your browser's localStorage. Nothing is sent to any server. Clear your browser data to erase the log.

Can I use liters and kilometers instead?

This tool uses miles and US gallons. For L/100 km, divide 235.21 by your MPG result (e.g., 30 MPG ≈ 7.8 L/100 km).

How many fill-ups should I log for an accurate average?

At least three consecutive full fill-ups give a reliable baseline. The first entry is always approximate because the previous tank may not have been full.

MPG Calculator

Name: MPG Calculator
Availability: InStock
Author: Nham Vu

Enter your odometer readings and gallons pumped to calculate MPG and track fuel economy across multiple fill-ups.

Log a Fill-Up

Previous Odometer (mi)

Current Odometer (mi)

Gallons Filled

Price per Gallon (optional, $)

Fill-Up History

0 entries

No fill-ups logged yet. Calculate your first MPG above.

#	Miles	Gallons	MPG	Cost	Del

Saved!

Summary

Enter your odometer readings and gallons pumped to calculate MPG and track fuel economy across multiple fill-ups.

How it works

Enter your previous odometer reading (the mileage before this fill-up).
Enter the current odometer reading (the mileage after filling up).
Enter the number of gallons pumped at the station.
Click "Calculate MPG" to see your fuel economy for that tank.
Your result is saved to the fill-up log automatically.
Review average MPG across all logged fill-ups in the history table.

Use cases

Track fuel economy on a long road trip tank by tank.
Compare MPG before and after a tune-up or tire inflation.
Monitor fleet vehicle fuel efficiency over time.
Spot trends showing engine wear or driving habit changes.
Verify manufacturer EPA estimates against real-world driving.
Calculate cost per mile when combined with current gas prices.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu