I know there's no exact answer to this question, but please try anyway.

Is there a way you can approximately figure out what the pressure in your cylinder be by using your compression ratio?

If you can fill me in on the formula that would be great or figure it out for me.

The compression ratio is about 5.1

Any help would be great. Thanks.

Too many variables. But as a reference a DSM 1G 1.8 litre running 9.0:1 compression should test at 185lbs and a 1G 2.0 litre running the same compression should test at 192lbs.

5.1:1 seems very low, even for a supercharged/turbo engine. What's the engine in?

It's an engine from a 1948 Farmall H. I know it might not be the right forum to be in for a tractor, but engines are engines I guess.

Like was said, too many variables. Theoretically, if the cylinders filled completely on each intake stroke, and if the valves and rings sealed perfectly, and if the ambient barometric pressure were 14.7 psi, then your compressed pressure should be (14.7 x 5) - 14.7 = 58.8. In truth, we can't know how the cam timing events, ring and valve seal, and actual VE of the engine, so actual pressures could be widely variant.