Good bathroom storage starts with a tape measure.

It depends on what you can spare, wall or floor. An over-the-toilet unit adds shelves without using new floor space, but it is tall and top-heavy, so anchor it to the wall. A floor cabinet holds bulkier, heavier items and keeps them within reach. Our over-toilet vs floor storage comparison walks through the trade-offs.

The width of the wall or gap you want to fill, the ceiling height, the swing of every door nearby, and the toilet tank if the unit goes above it. For under-sink storage, measure the cabinet's inside width, depth and height, plus the position of the drain pipe, which is what keeps generic shelving from fitting. Our bathroom storage buying guide covers the rest.

Powder-coated steel, solid wood, bamboo and solid plastic resist moisture well. Laminated MDF and particleboard cost less but can swell at the edges once water gets in, so keep them away from the shower and out from under a sink that might drip. Running the fan after a shower helps any material last longer.