Fuel Economy Reading Correction Calculator
Fix your mpg after a tire size change. Use the calculator below. Results update as you type.
How the Fuel Economy Reading Correction Calculator Works
This calculator works by multiplying the displayed miles per gallon (mpg) by the tire-size correction factor. Larger tires make the trip computer under-report mpg.
- Enter the displayed fuel economy, for example 18 mpg (13.07 L/100 km).
- Enter the correction factor, for example 1.066.
- Read the corrected economy: 19.2 mpg.
- Read the corrected metric value: 12.26 L/100 km.
The Formula
The formula is Corrected mpg = Displayed mpg × Correction Factor. The metric form divides by the factor.
Corrected mpg = Displayed mpg × Factor Corrected L/100 km = Displayed L/100 km ÷ Factor L/100 km = 235.215 ÷ mpg (US)Worked example: 22 mpg × 1.045 = 23.0 mpg. In metric, 10.69 L/100 km ÷ 1.045 = 10.23 L/100 km.
The fuel used is measured correctly. Only the distance is wrong, so the correction follows the distance error.
Conversion Table
The conversion table corrects 8 displayed fuel economy readings in US mpg and L/100 km. Factors run from 0.980 to 1.066.
The 30 mpg row with a 0.980 factor drops to 29.4 mpg. Smaller tires make the trip computer report better economy than the vehicle achieves.
| Displayed mpg (US) | Factor | Corrected mpg | Displayed L/100 km | Corrected L/100 km |
|---|---|---|---|---|
| 18 | 1.030 | 18.5 | 13.07 | 12.69 |
| 18 | 1.066 | 19.2 | 13.07 | 12.26 |
| 22 | 1.030 | 22.7 | 10.69 | 10.38 |
| 22 | 1.045 | 23.0 | 10.69 | 10.23 |
| 25 | 1.020 | 25.5 | 9.41 | 9.22 |
| 28 | 1.030 | 28.8 | 8.40 | 8.16 |
| 30 | 0.980 | 29.4 | 7.84 | 8.00 |
| 35 | 1.020 | 35.7 | 6.72 | 6.59 |
What Is the Fuel Economy Reading Correction Calculator?
The Fuel Economy Reading Correction Calculator is a tool that fixes trip computer and hand-logged fuel economy after a tire size change. Fuel economy is distance divided by fuel, so a distance error creates the same percentage economy error.
Bigger off-road tires often lower real fuel economy through weight and rolling resistance. The calculator separates that real loss from the reading error.
Common Uses
This calculator has 4 uses: real-loss measurement, fleet fuel reports, trip logs and before-and-after tests.
- Measure real losses: Find the true economy drop from bigger tires.
- Report fleet fuel use: Correct per-vehicle mpg.
- Correct trip logs: Fix fuel apps fed with odometer distance.
- Run before-and-after tests: Compare tires fairly.