Sneaky way to ask ring size

I ordered my spouse a ring, a promise ring kind of thing. I was a dummy & just guessed a size, I went for the recommended sizes for men on the site. He has pretty long thin fingers so I’m hoping a 10 fits.

Anyway, to verify this how should I ask him his ring size? I remember he told me but I forget! Play a game of 21 questions? Lmao. We’ve been together 4 years I feel like 21 questions is dumb lol