A storage basket fits the cabinet’s advertised depth but stops the door from closing. The missing measurement is often usable space: the room left after hinges, doors, shelves and services have taken their share.
Measure the path as well as the resting place
Open the door to the angle available in everyday use. Measure the narrowest opening the organiser must pass through, then the space where it will sit. A wide interior is not useful if a hinge or neighbouring handle prevents the item from entering.
Check depth at the intended height. A hinge may occupy space near the side, a pipe may cross the back, or a shelf support may interrupt the surface. Measure from the closed door’s inside position rather than assuming the cabinet front is the boundary.
Make a cardboard outline of the organiser’s footprint and height. Move it through the opening and test the closed-door clearance without forcing anything. Include handles, lids and any space needed to lift the contents out.
Think about the load in daily use
A pull-out basket needs clearance throughout its travel, not only when pushed in. Check the manufacturer’s installation and load requirements and whether the cabinet can support them. Do not drill around hidden services or modify a structural panel simply to make the purchase fit.
Under a sink, preserve access to valves, traps and service connections. An organiser that has to be dismantled before a leak can be reached creates a new problem. Keep cleaning products and other contents stored according to their labels and household safety needs.
Write the measurements on a small sketch, noting the obstructions rather than recording one optimistic rectangle. Take that sketch to the shop or compare it with the full product drawing. The best fit is the one that still works when the door is closed, the basket is loaded and someone needs the space behind it.