Fuel Economy Calculator
Track and analyze your fuel economy across multiple trips
Trip Log
Trip 1
Trip 2
Trip 3
Average Fuel Economy
25.2 MPG
Best: 25.7 | Worst: 25.0
Summary
Total Distance530 miles
Total Fuel Used21.0 gallons
Total Fuel Cost$73.50
Cost Per Mile$0.139
Projections
$1664
Est. Annual Cost
412 lbs
CO2 Emissions
What is Fuel Economy?
Fuel economy measures how efficiently a vehicle converts fuel into distance traveled. It's one of the most important factors in vehicle operating costs and environmental impact.
| Measurement | Unit | Interpretation | Used In |
|---|---|---|---|
| MPG (US) | Miles per gallon | Higher is better | United States |
| MPG (UK) | Miles per imperial gallon | Higher is better (1 imp gal = 1.2 US gal) | United Kingdom |
| L/100km | Liters per 100 kilometers | Lower is better | Europe, Canada, Australia |
| km/L | Kilometers per liter | Higher is better | Japan, South America |
Fuel Economy Formulas and Conversions
Master fuel economy calculations with these essential formulas:
| Calculation | Formula | Example |
|---|---|---|
| MPG | Distance (miles) ÷ Fuel (gallons) | 350 mi ÷ 12 gal = 29.2 MPG |
| L/100km | (Fuel in liters ÷ Distance in km) × 100 | (45L ÷ 560km) × 100 = 8.0 L/100km |
| km/L | Distance (km) ÷ Fuel (liters) | 560 km ÷ 45 L = 12.4 km/L |
| MPG to L/100km | 235.21 ÷ MPG | 235.21 ÷ 30 = 7.84 L/100km |
| L/100km to MPG | 235.21 ÷ L/100km | 235.21 ÷ 8 = 29.4 MPG |
| US to UK MPG | US MPG × 1.201 | 30 × 1.201 = 36.0 UK MPG |
Fuel Economy
MPG = Distance (miles) / Fuel (gallons)
L/100km = (Fuel in L / Distance in km) × 100
km/L = Distance (km) / Fuel (L)
Where:
- MPG= Miles per gallon
- L/100km= Liters per 100 km (lower is better)
Average Fuel Economy by Vehicle Type
EPA fuel economy ratings vary significantly by vehicle category:
| Vehicle Type | City MPG | Highway MPG | Combined MPG | L/100km |
|---|---|---|---|---|
| Compact Car | 28-32 | 35-40 | 30-35 | 6.7-7.8 |
| Midsize Sedan | 25-30 | 32-38 | 28-33 | 7.1-8.4 |
| SUV (Compact) | 24-28 | 30-34 | 26-30 | 7.8-9.0 |
| SUV (Full-size) | 16-20 | 22-26 | 18-22 | 10.7-13.1 |
| Pickup Truck | 15-19 | 20-25 | 17-21 | 11.2-13.8 |
| Hybrid | 45-55 | 45-52 | 45-55 | 4.3-5.2 |
| PHEV (gas mode) | 30-40 | 35-45 | 32-42 | 5.6-7.4 |
Factors Affecting Fuel Economy
Many factors influence your actual fuel economy compared to EPA estimates:
| Factor | Impact on MPG | Explanation |
|---|---|---|
| Aggressive driving | -15% to -33% | Rapid acceleration and hard braking waste fuel |
| Speeding (65→75 mph) | -7% to -14% | Air resistance increases exponentially with speed |
| Cold weather (20°F) | -12% to -22% | Engine takes longer to reach efficient temperature |
| Air conditioning | -5% to -25% | Greatest impact in extreme heat, stop-and-go traffic |
| Roof cargo | -2% to -8% | Even empty roof rack adds drag |
| Underinflated tires | -0.2% per PSI | 10 PSI low = -2% to -3% MPG |
| Extra weight | -1% per 100 lbs | Remove unnecessary cargo |
| Stop-and-go traffic | -10% to -40% | City driving vs highway significantly different |
How to Improve Fuel Economy
Practical strategies to maximize your MPG and reduce fuel costs:
| Strategy | Potential Savings | Implementation |
|---|---|---|
| Hypermiling techniques | 10-30% | Anticipate stops, coast to decelerate, maintain steady speed |
| Proper tire pressure | 3-4% | Check monthly, use manufacturer's recommended PSI |
| Regular maintenance | 4% | Air filter, spark plugs, oil changes per schedule |
| Use cruise control | 7-14% | Maintains steady speed on highways |
| Remove roof rack | 2-8% | Remove when not in use |
| Minimize idling | Variable | Turn off engine if stopped > 30 seconds |
| Plan trips efficiently | 5-10% | Combine errands, avoid peak traffic |
Calculating Annual Fuel Costs
Estimate your annual fuel expenses based on driving habits:
| Annual Miles | 25 MPG | 30 MPG | 35 MPG | 40 MPG | 50 MPG |
|---|---|---|---|---|---|
| 10,000 miles | $1,400 | $1,167 | $1,000 | $875 | $700 |
| 12,000 miles | $1,680 | $1,400 | $1,200 | $1,050 | $840 |
| 15,000 miles | $2,100 | $1,750 | $1,500 | $1,313 | $1,050 |
| 20,000 miles | $2,800 | $2,333 | $2,000 | $1,750 | $1,400 |
| 25,000 miles | $3,500 | $2,917 | $2,500 | $2,188 | $1,750 |
Based on $3.50 per gallon fuel price. Adjust proportionally for local prices.
Understanding EPA Fuel Economy Testing
EPA tests use standardized driving cycles that may differ from real-world conditions:
| Test Cycle | Duration | Distance | Top Speed | Average Speed |
|---|---|---|---|---|
| City (FTP) | 31 minutes | 11 miles | 56 mph | 21 mph |
| Highway (HWFET) | 13 minutes | 10 miles | 60 mph | 48 mph |
| High Speed (US06) | 10 minutes | 8 miles | 80 mph | 48 mph |
| Air Conditioning (SC03) | 10 minutes | 3.6 miles | 54 mph | 22 mph |
| Cold Temperature (Cold FTP) | 31 minutes | 11 miles | 56 mph | 21 mph |
Worked Examples
Calculate MPG from Trip Data
Problem:
You drove 427 miles on a road trip and filled up with 14.2 gallons. What was your fuel economy?
Solution Steps:
- 1Use the MPG formula: MPG = Distance ÷ Gallons
- 2MPG = 427 miles ÷ 14.2 gallons
- 3MPG = 30.07
- 4Compare to EPA rating to assess driving efficiency
Result:
Your fuel economy was 30.1 MPG, equivalent to 7.8 L/100km
Convert L/100km to MPG
Problem:
A European car is rated at 6.5 L/100km. What is that in US MPG?
Solution Steps:
- 1Use conversion formula: MPG = 235.21 ÷ L/100km
- 2MPG = 235.21 ÷ 6.5
- 3MPG = 36.19
- 4For UK MPG, multiply by 1.201
Result:
6.5 L/100km = 36.2 US MPG (43.5 UK MPG)
Calculate Annual Fuel Savings
Problem:
You're comparing a 25 MPG car versus a 35 MPG car, driving 15,000 miles/year at $3.50/gallon.
Solution Steps:
- 125 MPG: 15,000 ÷ 25 = 600 gallons × $3.50 = $2,100/year
- 235 MPG: 15,000 ÷ 35 = 428.6 gallons × $3.50 = $1,500/year
- 3Annual savings: $2,100 - $1,500 = $600
- 45-year savings: $600 × 5 = $3,000
Result:
The 35 MPG car saves $600 per year ($3,000 over 5 years)
Tips & Best Practices
- ✓Track your MPG over multiple fill-ups for accuracy—single tank calculations can vary by 5-10% due to pump shutoff differences
- ✓Check tire pressure monthly when tires are cold—underinflation by 10 PSI reduces MPG by 3% and accelerates tire wear
- ✓Remove roof racks and cargo boxes when not in use—even empty, they can reduce highway MPG by 2-8%
- ✓Use cruise control on highways to maintain steady speed—speed fluctuations waste fuel
- ✓Avoid excessive idling—restarting uses less fuel than idling for more than 30 seconds
- ✓Anticipate traffic and coast to stops rather than braking hard—regenerates some energy in hybrids
- ✓Check your car's actual MPG against EPA estimates at fueleconomy.gov to see how your driving compares to others with the same vehicle
Frequently Asked Questions
EPA tests are conducted in controlled laboratory conditions at moderate temperatures (68-86°F) with no accessories running. Real-world factors that reduce MPG include: aggressive driving (-15% to -33%), highway speeds over 50 mph, air conditioning use (-5% to -25%), cold weather (-12% to -22%), short trips where engine doesn't fully warm up, roof cargo, underinflated tires, and stop-and-go traffic. Most drivers achieve 10-15% below EPA combined rating.
UK imperial gallons are larger than US gallons (1 imperial gallon = 1.201 US gallons). The same car rated at 30 MPG in the US would be rated at 36 MPG in the UK. To convert: UK MPG = US MPG × 1.201. European L/100km is the same regardless of country. This difference is important when comparing international car reviews or purchasing imported vehicles.
Combined MPG is a weighted harmonic mean: Combined = 1 / ((0.55/City) + (0.45/Highway)). The 55%/45% weighting reflects typical driving patterns. For example, a car with 25 city and 35 highway: Combined = 1 / ((0.55/25) + (0.45/35)) = 28.7 MPG. This formula weights city driving more heavily because inefficient driving disproportionately affects the average.
No. If your car is designed for regular fuel (87 octane), using premium (91-93 octane) provides no benefit in power, MPG, or engine longevity. You're simply paying more per gallon. Only vehicles that require or recommend premium (typically high-performance or turbocharged engines) benefit from higher octane fuel, which prevents knocking in high-compression engines.
Most vehicles achieve peak fuel efficiency between 35-55 mph. Above 50 mph, every 5 mph costs approximately 7% more fuel due to exponential increase in aerodynamic drag. At 65 mph you use about 14% more fuel than at 55 mph. At 75 mph, you use about 28% more. For maximum fuel economy, use cruise control at 55-60 mph on highways when safe and legal.
For accurate tracking: 1) Fill tank completely at each fill-up (same pump position helps), 2) Record odometer reading at each fill, 3) Calculate MPG = miles driven ÷ gallons added, 4) Track over multiple fill-ups for accuracy (single tanks can vary 5-10%), 5) Use a fuel tracking app for convenience. Avoid topping off as it can skew readings. Winter and summer will show different MPG due to fuel formulations and temperatures.
Sources & References
Last updated: 2026-01-22