This calculator will tell you how much fuel of a certain type is needed to heat up a cold boiler to it's maximum temperature (Heatup Only), or tell you how long it will run with the given fuel (Fuel Simulation) or finally tell you how much fuel is required to keep the boiler running a set time (Time Simulation).
A few noteworthy things:
The formula for calculating fuel usage can be found on the Railcraft Wiki
Times are directly converted from ticks, this unless your server/client always run at peak tickrate (unlikely) times will vary slightly.
Fules values are kept up to date with the latest public Railcraft release. (Fuels from other mods are kept up to date as best I can.)
If you have a question, an issue or a feature suggestion (such as a specific fuel) you can post a comment and I will reply!