How to Calculate Your Car Gas Mileage (MPG)
Your actual MPG is 10-20% lower than the EPA sticker. Here is how to calculate your real fuel economy.
Fill your tank completely. Reset your trip odometer. Drive normally until you need gas again. Fill completely again and note the gallons. MPG = Miles driven / Gallons used. If you drove 320 miles and used 11.5 gallons: 320/11.5 = 27.8 MPG. Do this 3-4 times for an accurate average — one tank can vary based on city vs highway driving, weather, and traffic.
Why Your Real MPG Is Lower Than EPA
EPA tests are conducted in controlled lab conditions at moderate speeds with no AC. Real-world driving includes: aggressive acceleration (reduces MPG 10-33%), highway speeds above 60 mph (every 5 mph above 50 costs ~7% in fuel economy), AC use in summer (reduces MPG 5-15%), cold weather (reduces MPG 15-25%), and idling in traffic (0 MPG). Most drivers get 10-20% worse than the EPA estimate.
Easy MPG Improvements
Check tire pressure monthly (low tires cost 3% MPG). Remove roof racks when not in use (5-10% drag penalty). Drive 60-65 mph instead of 75 (15-20% savings). Combine errands into one trip. Use cruise control on highways. Do not idle for more than 30 seconds. These habits combined can improve MPG by 15-25% — saving $300-600/year in gas.