Check the specs, not the thickness.

The surest sign of soldered RAM is looking up the exact model’s specifications. Thinness is a clue (most ultra-thin laptops under 15mm have soldered RAM), but it’s not a rule — some thicker business laptops also solder it, and a few thin ones still have replaceable sticks.

If you can’t find a clearly marked RAM door on the bottom panel, that’s another hint. But the only way to know for sure is to look up the model number on the manufacturer’s site or a review from someone who’s already opened it. Guessing based on how it looks will waste your time (or void your warranty).

A few minutes of research beats prying open a sealed chassis.