how to calculate the genotypic ratio for F3 and F4 generations for a monohybrid cross?

Lets cross homozygous tall (TT) and homozygous short plants (tt) to get all tall plants (Tt) which are heterozygous. For F2 generation plants of F1 generation are selfed which gives a genotypic ratio of 1:2:1 (1TT : 2Tt : 1Tt). The genotypic ration in F3 generation can vary depending upon the type of plant which is crossed and same is the case for subsequent generations.