Fuel Economy Calculator

Calculate your vehicle This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Fuel Economy Calculator

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Fuel Economy Calculator?

A Fuel Economy Calculator computes your vehicle's MPG (miles per gallon), L/100km (liters per 100 kilometers), or km/L from odometer readings and fuel fill-ups. It also calculates per-mile fuel costs, annual fuel expenses, and CO2 emissions. In 2026, with fuel prices volatile and fuel economy standards tightening (CAFE standards targeting ~49 MPG fleet average), understanding your real-world fuel consumption — which often differs significantly from EPA estimates — helps with budgeting and vehicle purchase decisions.

How Does It Work?

Enter your odometer reading at fill-up and the gallons/liters of fuel purchased. The calculator computes: MPG = Miles Driven ÷ Gallons, or L/100km = (Liters ÷ Kilometers) × 100. For tracking over multiple fill-ups, it calculates a running average. The comparison feature lets you compare two vehicles: your current car vs. a car you're considering buying.

Formula

MPG (US) = Miles ÷ Gallons\nL/100km = (Liters ÷ Kilometers) × 100\nkm/L = Kilometers ÷ Liters\n\nConversions:\nMPG (US) = MPG (UK) × 0.833\n(UK gallon = 4.546L, US gallon = 3.785L)\nMPG (US) = 235.215 ÷ L/100km\n\nAnnual Fuel Cost = (Annual Miles ÷ MPG) × Price per Gallon\nCost per Mile = Price per Gallon ÷ MPG\n\nCO2 Emissions:\nPer gallon of gasoline: 8.887 kg CO2 (19.6 lbs)\nPer liter: 2.3 kg CO2\nAnnual CO2 = (Annual Miles ÷ MPG) × 8.887 kg

Who Uses This Tool?

• Car owners tracking real-world fuel economy vs. EPA estimates
• New car buyers comparing fuel costs between different vehicle models
• Budget-conscious drivers calculating annual fuel expenses
• Hyper-milers experimenting with driving techniques to improve MPG
• Environmentalists calculating and tracking driving carbon footprint

Pro Tips

• EPA estimates are based on standardized tests that may not reflect your driving. Real-world MPG is often 10-20% lower than EPA combined rating
• Track over multiple fill-ups — individual tank MPG can vary 20%+ due to pump shutoff differences. 5+ tank average gives reliable data
• Fuel economy drops ~15% at 70 mph vs. 55 mph. For highway driving, each 5 mph over 60 is like paying $0.20-0.30 more per gallon
• Winter fuel economy is worse: cold engines run rich, winter fuel blends have less energy, and increased electrical loads (lights, defroster) consume more fuel

Frequently Asked Questions about Fuel Economy Calculator

Why does my real MPG differ from the EPA rating?

EPA tests are conducted under controlled laboratory conditions. Real-world factors reduce MPG: aggressive driving, short trips (cold starts), idling, cargo weight, roof racks, under-inflated tires, and using AC. Expect 10-20% lower than EPA combined in normal driving.

What's the most fuel-efficient speed?

Most vehicles achieve peak fuel economy between 45-55 mph (72-89 km/h). Above 60 mph, aerodynamic drag (which increases with the square of speed) dominates and MPG drops quickly. Every 5 mph above 60 = ~7-10% MPG reduction.

Free online Fuel Economy Calculator — no signup, 100% client-side processing. All data stays in your browser.