Combined MPG Calculator
Combined MPG Calculator. Combine segments using fuel consumed. Enter your values and view the result.
Combined MPG Calculator
Combine segments using fuel consumed.
Use the calculation engine below to model your exact costs with custom fuel prices, distances, and vehicle efficiencies:
Combined MPG Calculator: inputs
Adjust sliders or enter exact figures
Monthly Fuel Budget
Real-Time Visual Breakdown
Comparing your expense against alternative vehicle classes
Price Fluctuation Stress Test
See how unexpected gas price surges would impact your monthly budget
How Combined MPG Calculator Works
This tool works by adding the fuel each segment consumes and dividing total distance by total fuel, which gives the true combined fuel economy.
- Step 1
Enter each segment
Add segments of driving or separate vehicles, each with distance and MPG.
- Step 2
Calculate fuel per segment
The calculator divides each segment distance by its MPG.
- Step 3
Sum distance and fuel
The calculator adds all distances and all fuel.
- Step 4
Read the combined MPG
The calculator shows combined MPG and the error of a simple average.
Combined MPG Calculator Formula
The formula divides total miles by total gallons consumed across segments.
Segment Gallons = Segment Miles ÷ Segment MPG
Combined MPG = Σ Segment Miles ÷ Σ Segment Gallons
- Segment
- = one part of the driving, or one vehicle in a group
- Segment MPG
- = fuel economy of that segment or vehicle
Worked Example
- A household has 2 cars: Car A drives 10,000 miles at 20 MPG; Car B drives 15,000 miles at 40 MPG.
- Car A uses 500 gallons; Car B uses 375 gallons; total = 875 gallons (3,312 liters).
- Combined MPG = 25,000 ÷ 875 = 28.6 MPG (8.2 L/100 km).
- A simple average of 20 and 40 gives 30 MPG, which overstates the combined figure by 1.4 MPG.
Combined MPG Calculator Conversion Table
The table compares the true combined MPG with a simple average for 2 segments of equal distance.
| Segment A MPG | Segment B MPG | Simple Average | True Combined MPG | Combined L/100 km | Overstatement |
|---|---|---|---|---|---|
| 10 | 30 | 20.0 | 15.0 | 15.7 | 33.3% |
| 15 | 45 | 30.0 | 22.5 | 10.5 | 33.3% |
| 20 | 40 | 30.0 | 26.7 | 8.8 | 12.5% |
| 20 | 50 | 35.0 | 28.6 | 8.2 | 22.5% |
| 25 | 35 | 30.0 | 29.2 | 8.1 | 2.9% |
| 30 | 50 | 40.0 | 37.5 | 6.3 | 6.7% |
What is a Combined MPG Calculator?
A Combined MPG Calculator is a fuel economy tool that combines segments or vehicles using the fuel each one consumes, not a simple average of MPG values.
MPG is a ratio, and ratios cannot be averaged directly. A segment at low MPG burns far more fuel per mile than a segment at high MPG, so the low figure must carry more weight. The Combined MPG Calculator sums fuel first, which gives the correct result.
The same method gives a fleet average fuel economy, which is how US Corporate Average Fuel Economy (CAFE) figures are built.
What are the uses of a Combined MPG Calculator?
There are 4 main uses of the Combined MPG Calculator, including household averages, fleet averages, and trip segment blending.
Average a household
Get one correct MPG for all household vehicles.
Average a fleet
Report fleet fuel economy with fuel-weighted math.
Blend trip segments
Combine towing, highway, and city segments of a trip.
Correct spreadsheets
Replace simple MPG averages in existing reports.