Calculate fuel economy, annual costs, and CO₂ emissions
Fuel economy is one of the most important factors in vehicle operating costs, and knowing your actual miles per gallon (MPG) helps you budget for fuel, compare vehicles, and make smarter driving decisions. Our free MPG Calculator computes your vehicle's fuel economy from any trip — simply enter the distance driven and fuel used, and get instant results in three global standards: US MPG, Imperial MPG, km/L, and L/100km. Beyond the basic fuel economy number, the calculator provides a comprehensive cost analysis. Enter your local fuel price and annual driving distance to see your cost per mile, cost per kilometer, annual fuel expenditure, and annual gallons consumed. An efficiency comparison bar chart shows how your vehicle stacks up against benchmarks for the average car (25.4 MPG), typical hybrid (50 MPG), average SUV (22 MPG), and average truck (18 MPG). The calculator supports three unit systems. US mode uses miles and US gallons. Imperial mode uses miles and Imperial gallons (common in the UK). Metric mode uses kilometers and liters. Regardless of which system you enter data in, all results are shown in all formats so you can compare with any vehicle specification worldwide. An environmental impact section estimates your annual CO₂ emissions based on the EPA factor of 8.887 kg CO₂ per gallon of gasoline burned, helping you understand the climate impact of your driving habits. The calculator auto-recalculates as you type, so results update in real time. All results can be exported to CSV for record-keeping or printed for reference. Track your MPG over multiple fill-ups to identify trends — a sudden drop in fuel economy often indicates a maintenance issue like underinflated tires, a dirty air filter, or a failing oxygen sensor.
Entendiendo la Eficiencia de Combustible
What Is MPG?
Miles per gallon (MPG) is the standard fuel economy measurement used in the United States. It represents the number of miles a vehicle can travel on one gallon of fuel. Higher MPG means better fuel economy — a car rated at 35 MPG uses less fuel per mile than one rated at 20 MPG. The US gallon (3.785 liters) is different from the Imperial gallon (4.546 liters) used in the UK, which is why the same vehicle will show a higher number in Imperial MPG than US MPG. The metric equivalent is kilometers per liter (km/L), while Europeans typically use liters per 100 kilometers (L/100km) — an inverse measure where lower numbers mean better efficiency.
How Is MPG Calculated?
The formula is simple: MPG = Distance driven (miles) ÷ Fuel used (gallons). For example, if you drove 300 miles and used 12 gallons, your fuel economy is 300 ÷ 12 = 25 MPG. To convert between standards: Imperial MPG = US MPG × 1.20095. km/L = US MPG × 0.425144. L/100km = 235.215 ÷ US MPG. Cost per mile = Fuel price per gallon ÷ MPG. Annual fuel cost = (Annual miles ÷ MPG) × Fuel price per gallon. Annual CO₂ = (Annual miles ÷ MPG) × 8.887 kg per gallon (EPA gasoline emission factor). For the most accurate MPG calculation, fill your tank completely, reset your trip odometer, drive normally until nearly empty, fill up again, and use the gallons from the second fill-up with the trip odometer reading.
¿Por qué Importa la Eficiencia de Combustible?
Fuel is typically the second-largest vehicle operating cost after depreciation. The difference between 20 MPG and 30 MPG over 12,000 annual miles at $3.50 per gallon is $700 per year — $3,500 over five years of ownership. Improving from 15 to 20 MPG saves even more ($1,400/year) because the relationship between MPG and fuel consumption is not linear: small improvements at low MPG values save more fuel than the same improvement at higher MPG values. This is called the 'MPG illusion' — going from 10 to 20 MPG saves 600 gallons per 12,000 miles, while going from 30 to 60 MPG saves only 200 gallons. Beyond cost, better fuel economy directly reduces CO₂ emissions and dependence on petroleum.
Measurement Notes
Real-world fuel economy varies significantly with driving conditions. Highway driving typically yields 10-30% better MPG than city driving due to less braking and acceleration. Cold weather, hilly terrain, heavy loads, roof racks, aggressive driving, and high speeds (above 50 mph, aerodynamic drag increases significantly) all reduce fuel economy. The EPA fuel economy ratings on new vehicle window stickers represent standardized test cycle results and are useful for comparing vehicles, but your actual MPG may differ by 10-20% depending on driving conditions and habits. For the most accurate personal fuel economy tracking, calculate MPG over multiple consecutive fill-ups and average the results to smooth out variations from different driving conditions.
Fórmulas
The basic fuel economy formula. Divide the total distance driven by the total fuel consumed to get miles per gallon.
Convert between US MPG, Imperial MPG (UK gallons), kilometers per liter, and liters per 100 kilometers. L/100km is an inverse metric — lower is better.
Estimates yearly fuel expenditure based on your MPG, annual driving distance, and local fuel price.
Estimates yearly carbon dioxide emissions using the EPA factor of 8.887 kg CO₂ per gallon of gasoline burned.
Reference Tables
MPG to L/100km Quick Reference
| US MPG | Imperial MPG | km/L | L/100km |
|---|---|---|---|
| 15 | 18.0 | 6.4 | 15.7 |
| 20 | 24.0 | 8.5 | 11.8 |
| 25 | 30.0 | 10.6 | 9.4 |
| 30 | 36.0 | 12.8 | 7.8 |
| 35 | 42.0 | 14.9 | 6.7 |
| 40 | 48.0 | 17.0 | 5.9 |
| 50 | 60.0 | 21.3 | 4.7 |
| 60 | 72.1 | 25.5 | 3.9 |
Average Fuel Economy by Vehicle Type (2024 US)
| Vehicle Type | Average MPG (Combined) | Annual Fuel Cost (at $3.50/gal, 12k mi) |
|---|---|---|
| Compact Car | 33 | $1,273 |
| Midsize Sedan | 30 | $1,400 |
| Full-size Sedan | 27 | $1,556 |
| Compact SUV/Crossover | 28 | $1,500 |
| Midsize SUV | 24 | $1,750 |
| Full-size SUV | 19 | $2,211 |
| Pickup Truck | 18 | $2,333 |
| Hybrid (non-plug-in) | 50 | $840 |
| Minivan | 22 | $1,909 |
Worked Examples
Basic MPG Calculation
MPG = Distance ÷ Fuel = 350 ÷ 13.2 = 26.52 MPG
Imperial MPG = 26.52 × 1.20095 = 31.84 MPG (Imperial)
km/L = 26.52 × 0.425144 = 11.27 km/L
L/100km = 235.215 ÷ 26.52 = 8.87 L/100km
Annual Fuel Cost Comparison
SUV: (15,000 ÷ 20) × $3.50 = 750 × $3.50 = $2,625/year
Hybrid: (15,000 ÷ 45) × $3.50 = 333.3 × $3.50 = $1,167/year
Annual savings: $2,625 − $1,167 = $1,458/year
5-year savings: $1,458 × 5 = $7,292
CO₂ Emissions Estimate
Annual gallons = 12,000 ÷ 28 = 428.6 gallons
Annual CO₂ = 428.6 × 8.887 = 3,808 kg
Convert to metric tons: 3,808 ÷ 1,000 = 3.81 metric tons CO₂
How to Use the MPG Calculator
Select Your Unit System
Choose US (miles and US gallons), Imperial (miles and Imperial gallons, used in the UK), or Metric (kilometers and liters). This determines the units for your distance and fuel inputs, but all results are shown in all formats regardless of selection.
Enter Trip Data
Enter the total distance driven and the total fuel used for the trip. For the most accurate result, fill your tank completely, note the odometer, drive until the next fill-up, and use the distance driven and gallons pumped at the second fill-up. Also enter your local fuel price and annual driving distance for cost calculations.
Revisa Tus Resultados
The hero result shows your MPG in US units, with Imperial MPG, km/L, and L/100km below. The efficiency bar chart compares your vehicle to benchmark averages. The cost breakdown shows per-mile cost, annual fuel expenditure, and annual gallons consumed. The environmental section shows annual CO₂ emissions.
Track and Export
Click 'Export CSV' to download your results for tracking fuel economy over time. Compare fill-ups to identify trends — consistent tracking can reveal maintenance issues early. Click 'Print' for a hard copy of your results.
Preguntas Frecuentes
How do I accurately calculate my car's MPG?
The most accurate method is the tank-to-tank calculation. Fill your fuel tank completely at the pump, then reset your trip odometer (or note the current odometer reading). Drive normally until you need to refuel. At the next fill-up, fill the tank completely again and note exactly how many gallons the pump shows. Divide the trip distance by the gallons pumped: MPG = Trip miles ÷ Gallons pumped. For even better accuracy, repeat this over 3-5 fill-ups and average the results. This smooths out variations from different driving conditions, routes, and temperatures. Avoid using the fuel gauge or trip computer — they are less accurate than pump measurements.
What is the difference between US MPG and Imperial MPG?
US MPG uses the US gallon (3.785 liters) while Imperial MPG uses the Imperial gallon (4.546 liters). Since the Imperial gallon is about 20% larger, the same vehicle will show approximately 20% higher MPG in Imperial units. A car that gets 25 US MPG gets about 30 Imperial MPG. The UK and some other Commonwealth countries historically used Imperial gallons, while the US uses its own gallon. When comparing fuel economy numbers from different countries, always check which gallon standard is being used. The metric system avoids this confusion by using liters — km/L or L/100km have only one standard worldwide.
¿Cuál es un buen MPG para un automóvil?
The 2024 US fleet average for all new cars and light trucks combined is approximately 25.4 MPG. A car achieving 30+ MPG is considered good by US standards. Hybrids typically achieve 45-55 MPG, and plug-in hybrids can exceed 100 MPGe (miles per gallon equivalent) when running on electricity. For sedans, 30-35 MPG is above average. For SUVs, 25-30 MPG is good. For trucks, 20-25 MPG is respectable. The most fuel-efficient non-plug-in cars on the market achieve 55-60 MPG. Context matters — a truck getting 22 MPG is performing well for its class even though a sedan at 22 MPG would be below average.
Why does my actual MPG differ from the EPA rating?
EPA fuel economy numbers are measured under standardized laboratory conditions using prescribed driving cycles, not on real roads. Several factors cause real-world MPG to differ: aggressive acceleration and braking (can reduce MPG by 15-30%), highway speeds above 50 mph (each 5 mph above 50 costs roughly 2-4% in fuel economy due to aerodynamic drag), cold weather (winter fuel blends have less energy per gallon, cold engines are less efficient, and tire rolling resistance increases), short trips (engines run less efficiently when cold), mountainous terrain, heavy loads, underinflated tires, and accessory use (air conditioning can reduce MPG by 3-5%). Gentle driving, proper tire inflation, and highway cruising typically yield MPG close to or above the EPA highway rating.
How do I convert MPG to L/100km?
The conversion formula is: L/100km = 235.215 ÷ MPG (US). For example, 30 US MPG = 235.215 ÷ 30 = 7.84 L/100km. For Imperial MPG: L/100km = 282.481 ÷ MPG (Imperial). The inverse relationship means that lower L/100km values indicate better fuel efficiency (opposite of MPG where higher is better). European fuel economy labels use L/100km as the standard. Approximate equivalents for reference: 20 MPG ≈ 11.8 L/100km, 25 MPG ≈ 9.4 L/100km, 30 MPG ≈ 7.8 L/100km, 35 MPG ≈ 6.7 L/100km, 40 MPG ≈ 5.9 L/100km, 50 MPG ≈ 4.7 L/100km.
Does driving slower always save fuel?
Yes, but with diminishing returns below about 35-40 mph. Fuel consumption has two main components: engine friction (dominant at low speeds) and aerodynamic drag (dominant at high speeds). The aerodynamic drag force increases with the square of speed, so doubling speed quadruples drag. Most vehicles hit their peak fuel efficiency between 35-55 mph. Above 50 mph, every additional 5 mph costs roughly 2-4% in fuel economy. At 75 mph, a car typically uses 20-30% more fuel than at 55 mph for the same distance. However, driving extremely slowly (under 25 mph) in high gears is also inefficient because the engine operates outside its optimal efficiency range. The sweet spot for most vehicles is steady cruising at 45-55 mph in the highest gear — which is why highway MPG ratings are often tested at 48 mph average speed.