It’s not always about size, but sometimes it is.
Think about the condoms you and/or your partner normally use—that'll help narrow down which Ohnut will be most comfortable! When in doubt about sizing, order the Wider Ohnut. It's unlikely to be too wide for effective use.
Classic: "Standard" or "regular" condoms; Lifestyles Snugger Fit, Slim Fit, or similar
Wider: Trojan Magnum, Durex XXL, or similar; or if a looser fit is preferred.
The Wider Ohnut is 15% wider than the Classic Ohnut and stretches up to 50% more.
All Ohnuts are made with a soft material that stretches significantly for comfort.