Gas Mileage Calculator
Calculate your vehicle's MPG, km/L, and L/100 km from a real fill-up. Includes annual fuel cost estimate and CO₂ per mile output.
📈 Typical MPG by Vehicle Type (2025)
| Vehicle Type | City MPG | Highway MPG | Combined MPG |
|---|---|---|---|
| Compact / Economy Car | 3035 | 3845 | 3340 |
| Midsize Sedan | 2530 | 3438 | 2833 |
| Hybrid (e.g. Toyota Prius) | 5357 | 5255 | 5256 |
| Compact SUV / Crossover | 2227 | 2934 | 2530 |
| Full-Size Pickup Truck | 1518 | 2024 | 1721 |
Indicative ranges only. Source: fueleconomy.gov. Updated January 2026.
How to Accurately Calculate Your Gas Mileage
The most accurate way to calculate fuel economy is the fill-up method: fill your tank completely, reset your trip odometer to zero, drive normally, then fill up again completely. MPG = Miles driven ÷ Gallons added. Do this over 3–4 fill-ups and average the results to account for variation in driving conditions.
Why Your Real MPG Differs from the Window Sticker
EPA fuel economy estimates are tested on a dynamometer under controlled conditions. Real-world driving differs for several reasons: Speed — every 5 mph above 50 mph costs about 7–14% in fuel efficiency. Acceleration — aggressive starts can reduce MPG by 15–40%. Cold weather — gasoline engines are 15–25% less efficient until fully warmed up; short trips under 5 miles rarely warm the engine fully. Air conditioning — reduces MPG by 5–25% depending on the vehicle. Tire pressure — under-inflated tires cost about 0.2% per PSI below specification.
The Cost Difference Between 25 MPG and 35 MPG
At 15,000 miles/year and $3.50/gallon: 25 MPG costs $2,100/year in fuel; 35 MPG costs $1,500/year — a $600/year difference. Over 5 years, that's $3,000 in savings, which can more than justify choosing a more fuel-efficient vehicle. Our calculator shows exactly how much you spend and save with any MPG or price change.
What Affects Gas Mileage (MPG)?
Gas mileage measures how efficiently a vehicle converts fuel into distance. The EPA's official MPG ratings are measured in standardized lab conditions; real-world MPG is typically 15–20% lower. Key factors that reduce MPG include aggressive acceleration and braking (can reduce MPG by 15–30% in city driving), highway speeds above 60 mph (aerodynamic drag increases exponentially with speed), running the air conditioner (reduces MPG by 5–25% depending on temperature), carrying extra weight (every 100 lbs reduces MPG by about 1%), and using roof racks when empty (adds drag, reducing highway MPG by 5–10%).
How to Calculate Your Actual MPG
The most accurate method: fill your tank completely, reset your trip odometer to zero, drive normally until you need to refuel, fill the tank again and note the gallons added, divide the miles driven by gallons added. MPG = Miles Driven ÷ Gallons Used. Do this over 3–5 tanks to get an accurate average. Many modern vehicles display real-time and trip MPG on the dashboard — these readings are typically accurate to within 1–3% of the calculated method.
MPG vs L/100km vs km/L — Quick Conversion
Different countries use different fuel economy units. To convert between them: MPG (US) to L/100km: divide 235.2 by MPG. L/100km to MPG: divide 235.2 by L/100km. MPG (US) to km/L: multiply by 0.4251. A 30 MPG vehicle equals 7.84 L/100km or 12.75 km/L. The "better" number for L/100km is lower (less fuel per distance); for MPG and km/L, higher is better. Always verify which gallon standard is being used — US gallons (3.785L) vs Imperial gallons (4.546L) cause a 20% difference in stated MPG.
