Formula
Miles and gallons divide. Liters per 100 kilometers scale the distance:
fuel = distance / MPG × (1 + reserve)
The metric form is distance / 100 × L/100 km, then the same reserve. The fuel cost page prices the fuel and does not add a reserve.
Assumptions
- Economy stays constant.
- The reserve is extra fuel, not a price.
- Miles stay with miles per gallon, and kilometers stay with liters per 100 km.
Worked example
300 miles at 30 mpg, plus a 10% reserve, needs 11 gal.
Input definitions
- Reserve
- A percent added on top of the fuel the economy implies.
- Economy
- Miles per gallon, or liters per 100 kilometers, matching the unit pair.
Limitations
Hills, load, and wind can use more fuel than the reserve. This is not a station price.
Questions
Why is there no price?
The result is volume. The fuel cost page multiplies volume by a price and does not add a reserve.
What does the reserve change?
Ten percent makes the fuel one-tenth larger than distance divided by economy.