Gas Mileage Calculator
Last Updated:
Calculate your real-world fuel efficiency (MPG) from actual fill-up data. Shows cost per mile and per 100 miles.
Fuel Efficiency
25.0 MPG
📐 Formula
MPG = Miles Driven ÷ Gallons Used. Cost per Mile = (Gallons × Price) ÷ Miles
How to Use the Gas Mileage Calculator
Record your odometer at fill-up
Note the odometer reading each time you fill your tank completely. The calculator uses the difference between two consecutive readings to determine miles driven.
Enter gallons added
Input the exact number of gallons (or litres) added at the fill-up. This is printed on your fuel receipt. For accuracy, always fill the tank completely before calculating.
Enter fuel price
Input the price per gallon or litre to also calculate your cost per mile — a useful metric for comparing vehicles and planning fuel budgets.
Track multiple fill-ups
MPG varies significantly fill-to-fill based on driving conditions. Track 3–5 consecutive fill-ups for an accurate average. A single calculation can be misleading if the previous fill was partial.
MPG vs L/100km: Understanding Both Systems
The US uses miles per gallon (MPG) — higher is better. Most of the world uses litres per 100 kilometres (L/100km) — lower is better. Converting between systems: L/100km = 235.2 ÷ MPG. So 30 MPG = 235.2 ÷ 30 = 7.84 L/100km. A 50 MPG hybrid = 4.7 L/100km. An inefficient 15 MPG truck = 15.7 L/100km.
MPG is counterintuitive for comparing efficiency improvements. Going from 10 to 20 MPG saves far more fuel per mile than going from 30 to 40 MPG — yet both are "10 MPG improvements." The L/100km system makes this clearer: 10 MPG = 23.5 L/100km; 20 MPG = 11.8 L/100km (saving 11.7 L/100km). The 30→40 MPG improvement: 7.84→5.88 L/100km (saving only 1.96 L/100km). The most fuel savings come from improving the least efficient vehicles.
EPA Ratings vs Real-World Fuel Economy
EPA fuel economy estimates are measured on a dynamometer under standardised driving cycles. Real-world results typically differ. The five-cycle test (introduced 2008) is more accurate than the older two-cycle test, but still varies from real driving. Key factors: highway speed (EPA highway test averages around 48 mph — driving at 75 mph reduces highway MPG significantly), air conditioning (EPA tests don't always reflect heavy AC use in hot climates), short cold trips (city MPG is heavily penalised by cold engine warm-up cycles), and individual driving style. fueleconomy.gov allows users to submit real-world MPG reports — check these community averages for your specific vehicle model for a realistic expectation.
Calculating Your Annual Fuel Cost
Annual fuel cost = (Annual miles ÷ MPG) × average gas price. The average US driver covers approximately 14,500 miles per year. At 28 MPG and $3.50/gallon: (14,500 ÷ 28) × $3.50 = 517.9 gallons × $3.50 = $1,813/year. At 20 MPG: $2,538/year — a $725 annual difference. Over five years and 72,500 miles, the 20 MPG vehicle costs $3,625 more in fuel alone. This is why fuel efficiency is a significant factor in vehicle total cost of ownership, particularly for high-mileage drivers.
Sources & Methodology
Calculations are based on the most current publicly available data from authoritative government and industry sources:
Frequently Asked Questions
Fill up your tank completely and reset your trip odometer. Drive normally until you fill up again. Divide the miles driven by the gallons it took to refill. That's your real-world MPG.
For 2024: compact sedans 30–40 MPG, SUVs 22–28 MPG, trucks 18–25 MPG, hybrids 40–55 MPG. The EPA rates vehicles under controlled conditions; real-world MPG is typically 15–20% lower.
MPG varies with speed (highway vs city), temperature (cold engines use more fuel), load (extra passengers or cargo), driving style, AC use, and tire inflation.