Microwave Oven Transformer Calculations
It looks like you already wound the secondary. I think you probably know how many turns you have on the secondary or can count them pretty easily since there are just a few. So just measure the primary and secondary voltages while the secondary is open-circuited. Then you can calculate the primary turns using the basic voltage equation for transformers.

V1/N1 = V2/N2

Where V1 is the primary voltage, N1 is the number of turns on the primary, V2 is the secondary voltage, and N2 is the number of turns on the secondary. Just rearrange the equation to solve for N1.

Be careful not to get shocked by the primary side.