Im making an ijn destroyer, the bb Yashiro and the Akagi at the moment. All in 700 scale.The kits all appear to have different porthole sizes ( where they exist. )

Can someone give me some indication of what size they should be and what drill size would be most accurate in scale?

Appreciated

Hello Alen - not trying to be funny, but it would appear that like myself, you're over complecating things where the drill bits against what size they should be situation, stand back and look at t this way - if you brought yourself a box of jewellers wire gauge HSS twist drills from ebay ie Microbox you're looking at sizes 61-80, these are cheap please let me know how you got on, you'll also need a pin-vice again cheap go for the double headed type but with these, generally, you'll get what you pay for.
When your twist bits arrive, simply look, pull one out and size against the blank on the hull of the ship, its that easy.

Above simply following the existing but filled in portholes, I drilled these out on my 1-700 cruiser.

While I have the typical obsessive compulsive traits of a ship modeler its not really about that.
I have the bits and a pin vice but Id rather not ruin work by using the wrong diameter drill. Id just rather be authentic than guestimate something like that.
From a bit of maths and help over at modelwarships is seems a 77 bit is closest to a 12 inch porthole used by IJN but a bit of artistic vision cant hurt I guess

Nice work on that cruiser thanks for the advice

I found that investing in a gauge really pays for itself when/if you repeat tasks and take some time between builds. I also recommend getting a collate for your Dremel-type rotary tool, and trying that instead of pin vise/wrist action. Of course, the rotary tool has to be the slow-speed type or you will simply melt the plastic

I bought a vernier calliper in the last month and a dremel 400 just a day ago. not had time to play with it yet In 700 scale I need those callipers ++.