Measuring compression ratio

[J_PEPIN87]

I'm finally putting together my 427bb, i already have the heads torqued down and going to start putting everything else on it.the problem i have is that i have no idea what my compression ratio is i'm just guessing.can someone please explain to me what i have to measure and the formula.also my machinist gave me a gasket set but it looks cheap to me and i cant find what the head gasket thickness is. The part number of the gaskets is 260-1009 is on summit wat yall think about them?thanks in advance