Do engagement rings fit tighter in cold weather or is that a myth?

A size 6 ring at 35°F is still a size 6 ring, but your finger isn't. So no, cold weather does not make an engagement ring fit tighter. It does the opposite.

What cold actually does

Cold constricts the blood vessels in your fingers. That's simple circulation, not jewelry. When your hands get cold, your fingers lose circumference and the ring usually feels looser, which is why I've had people panic about losing rings while shoveling snow in February. The metal also contracts, but not in any way you'd notice. An 18k gold band with a 17mm inside diameter will contract maybe 0.01mm between body temperature and freezing, which is less than the tolerance on any mandrel I own.

Why rings can feel tighter anyway

Where the tighter feeling comes from is the thaw. You come inside from a walk, your hands start warming up, circulation returns all at once, and the finger swells a little, which makes the ring feel snug for an hour or two. That's not the cold making it tight. That's the rebound. And in winter, that rebound is more dramatic because the temperature swing is bigger.

Last February a woman named Dana came in certain her ring had shrunk half a size. It hadn't. Her hands were just cold, and the ring was slightly too small for her normal summer finger. She'd been wearing it since December and only noticed the fit once she started comparing it to her other rings indoors.

If your ring is genuinely hard to get over the knuckle in winter, the problem isn't the season. It's the size. A ring that's comfortable only when your hands are cold is too small for the other 11 months of the year. I'd rather size someone up a quarter size and add a small bead or sizing assistant than send them out with a ring that fights them in summer.

Buy for July hands, not January hands.