Caluclations (sorry for bad grammar)

[alpha tech]

I have been using the Fasa Apollo mod and have got pretty good at translunar injections but I just cant figure out how to calculate them and also some other formulas like how to calculate delta v and twr and etc..

[Padishar]

Try this page

http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet

...and various others on the wiki.

[alpha tech]

I have tried that that's where I got the formula for the delta v and when I use mechjeb it gives me a totally different number

[ghpstage]

I have tried that that's where I got the formula for the delta v and when I use mechjeb it gives me a totally different number

Both mechjeb and KER have the ability to give your total dV at a specific altitude, which isn't very useful in most circumstances. Assuming you are calculating vacuum dV check your mechjeb isn't in atmospheric mode.

Aside from that you may be making mistakes in your calculations, common ones include,

Using local gravity values instead of 9.81,

Forgetting the 'ln' function,

Adding together the ISP of multiple engines on the stage, the proper way to deal with it is in the link already given

Edited November 6, 2015 by ghpstage

[Padishar]

Your best bet is to do a few very simple examples, e.g. just a pod, a fuel tank and an engine. You should be able to get the calculation correct for that. Note that strictly speaking the value of g used in the game is 9.80655 and some of the stock mass displays are not totally accurate, e.g. tons with 2 decimal places has a resolution of 10kg.