Measuring a Single Speed Chain with Chain Tensioner

I have a bike with vertical drop-outs and I wanted to change it to a single speed. I wanted to ask how I should measure the chain to work with a chain tensioner. Should I measure the chain around the cog and chain ring and add a number of pins? Or should I negate the extra pins and then add the tensioner after? Thank you for the help. (For reference, it is going to be a 36-16 ratio)