How to Convert Kilometers/Kilogram (km/kg) to Miles/Gallon (MPG)

Question

I need to convert Kilometers per Kilogram to Miles per Gallon in order to calculate the Carbon Footprint of daily work commuters with vehicles using CNG (Nat Gas).

In order to do this, I need to be able to figure the density of CNG. But, I am unsure of the pressure. The commuters are driving Natural Gas Vehicles. (http://www.fueleconomy.gov/feg/bifueltech.shtml)

Not sure if this is correct, but I found this information: Mass density (kg/m³) = 0.712 from (http://www.unitrove.com/engineering/tools/gas/natural-gas-density)

The data entered by the users ranges between 8 and 20. Therefore, the result should come up with a similar number to miles per gallon.

Answer 1

km/kg to miles/gallon (US)

1 km = 0.621371 mile

1 gallon = 0.00378541 m^3  therefore  m^3 = 1 gallon / 0.00378541

gas density = 0.712 kg/m^3 = 0.712 kg / (1 gallon / 0.00378541)
            = 0.00269521192 kg/gallon

Set the above to 1, rearrange for kg and substitute:

km/kg = 0.621371 mile / 371.028338284 gallon = 0.0016747... mile/gallon

Answer 2

$$1\frac{\text{km}}{\text{kg}}=1\frac{\text{km}}{\text{kg}}\cdot\frac{0.712\text{kg}}{\text{m}^3}\cdot\frac{\text{mi}}{1.60934\text{km}}\cdot\frac{\text{m}^3}{264.172\text{gal}}=0.0016747\ldots\frac{\text{mi}}{\text{gal}}$$