TPT physics differs significantly from real-world physics, so using realistic parameters for mass, thrust, and the like makes no sense.
For elements that have a clear real-world equivalent, you can use their actual density; however, to determine their mass, you also need to know the size of a single pixel - a value that is likewise unknown. Consequently, if you want to measure a rocket's thrust, you will likely have to devise your own physical quantities based on the physics within TPT - quantities that would almost certainly make no sense in real-world physics.