Oil Pressure / Water Pressure / Boost Pressure ( Turbo Engine )
You math checks you to me.

When you code it, You will probably read a voltage using an analog pin (or external ADC) that will return an integer between 0 being 0 volts, and 1024 = vin volts. vin will be 5 if you don't wire up the vin pin, and 1024 could be different if you use an external ADC.

Anyway you should be aware that the raw readings will probably not be 0-5, and they dont have decimal points. You will need to first convert the reading into the voltage with something like this:

float voltage = ((float)reading)/1024.f;


notice that the datatype float is used (enables decimal points) and that the constant being divided by is also a float so that the calculations will definitly happen between floating point numbers.