Under-sink cabinets rarely provide one clean rectangular space. Pipes and hardware divide the opening into smaller zones, so the most useful measurements describe each usable section.
Measure through the door frame
Record the clear opening width and height, not only the wider cabinet interior. Check hinges and the angle needed to place an assembled organizer inside. A product can fit once installed but fail to pass through the opening.
Map every obstruction
Measure the position of supply lines, shutoff valves, drains, traps, disposals, filters, hoses, and the sink bowl. Sketch their distance from the cabinet walls, floor, and doors so a shelf or drawer does not block service access.
Test pull-out clearance
Confirm that doors open far enough and that the organizer can slide without striking hinges, plumbing, or the cabinet frame. Include bottle height on both fixed and moving tiers.
Keep plumbing accessible
Organization should not hide leaks or prevent quick access to shutoff valves and drain fittings. Avoid loading products against pipes, and periodically remove supplies to inspect the cabinet floor for moisture.