Thanks for the link Janet.
My sarcastic reply was off-base: For some reason I thought it was a US organization requiring a non-US standard size. This, of course, is a UK portrait gallery, and of course wants a UK standard size for the entries.
I believe that 12x16 paper is smaller than A3, and might disqualify you. Play it safe, get 16x20 paper, buy yourself a decent easel or get some coated glass and go for it. And, good luck!
And Mike: Yes, I realize that the US is (still) out of step with the rest of the world... It's a never ending source of frustration for me, who lives on two continents. Videos, electric appliances, envelopes and paper sizes, cell phones, etc., etc., are all incompatible... I need two sets of a lot of things that I really shouldn't.
Best,
Doremus Scudder
www.DoremusScudder.com
Best