A pair of dumbbells can feel light in a squat and surprisingly demanding in an overhead press. That is the difficulty with shopping for a single number. The number describes the object; it does not describe every exercise you might perform with it.
Write down the movements you already know and expect to practice at home. Perhaps those are a squat, a row and a floor press. If the list contains unfamiliar lifts, learn their basic setup before choosing resistance for them. A weight bought for an imagined future routine may sit unused because it does not suit the routine you can actually perform.
Try the least convenient part
When possible, handle a prospective dumbbell in person. Check whether you can wrap your hand around the grip without crowding your fingers against the ends. Notice the texture with dry hands. A thick handle can be difficult to hold even when the load itself is manageable.
Then think beyond the repetition. Can you pick it up from its storage position, carry it to the exercise area, and set it down under control? A purchase that requires an awkward lift from a deep cupboard creates a problem before the session begins. The footprint matters as well: some adjustable models remain long at light settings and can feel crowded when held close together.
For a first purchase, favor a load you can control in the intended movement rather than the heaviest one you can move once. A demonstration with one easy repetition is not enough to tell you how the later part of a set will feel. Ask a qualified instructor to help with selection if you have no reference point.
One pair does not have to do everything
There are several reasonable compromises. You can buy a pair that suits a few upper-body movements and practice lower-body patterns without added weight. You might choose one heavier dumbbell for two-handed exercises. An adjustable pair offers more settings but also introduces a mechanism that needs correct use and inspection.
Avoid solving a mismatch by moving faster, swinging the weight, or shortening a movement simply to keep using the purchase. Different exercises can require different loads. It is normal to leave one exercise unloaded while using resistance for another.
Before ordering, make room for the equipment you have chosen. Check the storage load limit and keep weights low, stable and outside walkways. The first pair should make a handful of useful exercises available without making the room harder to live in.
