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Fuel Economy Calculator

Calculate MPG from miles driven and gallons used, estimate fuel cost, and compare two vehicles side by side to see annual savings from better efficiency.

Planning trip or annual fuel budget in dollars?

This page calculates MPG and compares vehicles. For trip, monthly, and annual fuel cost from distance and efficiency, use the Fuel Cost Calculator →

What is Fuel Economy?

Fuel economy is distance per unit of fuel — MPG in the US or L/100km in Europe. This calculator has three tabs: compute MPG from an odometer reading and fill-up, estimate fuel cost from MPG and distance, and compare two vehicles’ annual fuel spend to quantify upgrade savings.

Use this page when the primary question is “what is my MPG?” or “how much would I save switching from a 22 MPG SUV to a 40 MPG hybrid?” Real-world MPG is often 10–20% below EPA ratings because of speed, AC, and driving style.

For a dedicated trip and annual cost planner with metric/imperial toggles and monthly budgeting, use the Fuel Cost Calculator. To measure L/100km from litres used on a specific journey with full unit conversion, use the Fuel Consumption Calculator.

How the Fuel Economy Calculator Works

Formula, assumptions, and calculation steps for this automotive tool.

Formula Used

MPG = Miles Driven / Gallons Used

Methodology

Divides distance traveled by fuel consumed to compute miles per gallon or liters per 100 km.

Calculation Steps

  1. Enter distance, fuel use, price, payment, or vehicle value assumptions.
  2. Normalize miles/kilometers, gallons/liters, and monthly periods.
  3. Apply the relevant cost, efficiency, or depreciation formula.
  4. Show per-trip, monthly, or ownership totals.

Assumptions and Limits

  • Fuel prices, insurance, taxes, and resale values change over time.
  • Driving style and maintenance history affect real costs.
  • Use results for planning and comparison.

Frequently Asked Questions

For 2024 model year vehicles: compact cars average 30–40 MPG combined, midsize SUVs 25–30 MPG, full-size trucks 18–24 MPG, and hybrids 45–60 MPG. The EPA calculates a combined rating at 55% city / 45% highway. Real-world MPG typically runs 10–20% below the EPA estimate due to higher speeds, AC use, cold starts, and individual driving style.

Fill your tank completely, reset your trip odometer to zero, drive normally, then fill up again. Record the miles on the odometer and the gallons needed to refill the tank. MPG = Miles driven / Gallons used. For greater accuracy, average 3–5 tanks of data. A single fill-up can be skewed by topping off technique.

L/100km measures how many litres of fuel are used per 100 kilometres — lower is better. To convert MPG to L/100km: L/100km = 235.21 / MPG. So 30 MPG = 235.21 / 30 = 7.84 L/100km. European fuel economy labels use L/100km; Canadian labels use L/100km; US labels use MPG.

At 15,000 miles/year and $3.50/gallon: 20 MPG costs $2,625/yr, 30 MPG costs $1,750/yr, 40 MPG costs $1,313/yr. The savings from improving from 20 to 30 MPG ($875/yr) are greater than improving from 30 to 40 MPG ($437/yr) — the relationship is hyperbolic. The biggest gains come from replacing low-MPG vehicles.

Real-World Applications

🚗
New Vehicle Purchase Decision
Compare the 5-year fuel cost difference between two vehicles to quantify how quickly a more fuel-efficient model pays back its higher purchase price.
📏
Personal MPG Measurement
Calculate your actual fuel economy by recording miles driven and fuel added across a fill-up cycle to compare against manufacturer ratings.
🌍
International Unit Conversion
Convert between US MPG, UK MPG (Imperial), L/100km, and km/L to compare vehicles across different regional markets.
🔧
Maintenance Impact Tracking
Track MPG before and after a tune-up, tyre inflation check, or filter replacement to verify that maintenance improved fuel economy.
💼
Business Mileage Reimbursement
Calculate the IRS standard mileage rate reimbursement value and compare it to actual fuel cost per mile to evaluate vehicle cost recovery.
🌱
Carbon Footprint Estimation
Convert MPG to grams of CO₂ per mile to assess and compare the environmental impact of different vehicle choices.

Common Mistakes

1
Trusting the dashboard MPG display
Onboard computers estimate MPG from fuel injection data and can be 5–15% optimistic compared to calculated tank-to-tank measurements.
2
Measuring over too short a distance
Short-trip measurements are heavily distorted by cold engine warm-up cycles. Measure over at least 200–300 miles for a reliable average.
3
Not standardising driving conditions
Comparing MPG from a highway road trip to a city commute week is not meaningful — compare like-for-like driving patterns for valid comparisons.
4
Ignoring the effect of ethanol blends
E10 fuel (10% ethanol) contains ~3% less energy than pure petrol — vehicles typically achieve 2–3% lower MPG on E10 vs regular petrol.
5
Not filling the tank completely before measuring
For accurate fill-to-fill MPG calculations, the tank must be filled to the same level at the start and end of the measurement period.

EPA MPG Benchmarks by Vehicle Class (2024)

Class City MPG Highway MPG Combined MPG
Compact Car 28–34 36–44 31–38
Midsize Sedan 24–30 33–40 27–34
Large SUV 16–20 22–27 18–23
Midsize Pickup Truck 17–21 22–28 19–23
Full Hybrid 40–50 38–48 40–50
Plug-in Hybrid 55–100 MPGe 40–55 MPGe 50–90 MPGe

References

  1. U.S. Environmental Protection Agency. Fuel Economy Testing and Labeling. EPA, 2024.
  2. U.S. Department of Energy. Factors That Affect Fuel Economy. fueleconomy.gov, 2024.
  3. Consumer Reports. How We Test for Fuel Economy. Consumer Reports, 2024.
  4. AAA. Impacts of Air Conditioning on Fuel Economy. AAA, 2023.
  5. Oak Ridge National Laboratory. Transportation Energy Data Book. ORNL, 2023.

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