Corner storage is governed by two walls and the room in front of them. A unit can fit each wall measurement separately and still project too far into a walkway or fail to sit square.
Measure both wall runs
From the corner, record clear distance along each wall at the floor and at shelf heights. Note trim, outlets, switches, windows, vents, and anything that prevents the unit from reaching the corner.
Check whether the corner is square
Walls can bow and corners can be wider or tighter than ninety degrees. Compare measurements at several heights and expect a rigid furniture back to reveal gaps that a flexible visual estimate hides.
Mark the diagonal projection
Use tape to mark the unit's front edge or widest shelf in the room. Open nearby doors and drawers and walk past the outline. Projection often matters more than wall width in a small room.
Plan the assembly route
Tall corner towers may need floor area to assemble and enough ceiling clearance to stand upright. Measure doorways and turns, and check whether the finished unit can be positioned without scraping walls.
Match load to installation
Compare per-shelf and total limits and follow instructions for leveling, wall mounting, or tip restraint. Distribute heavy items as directed and keep breakable objects away from collision-prone corners.