Enter your cabinet opening dimensions and slide type to get exact drawer box sizes.
Drawer slide type
About the bottom panel dado
Before assembly, cut a 1/4"-wide × 1/4"-deep groove on the inside face of all four pieces, 1/4" up from the bottom edge. The bottom panel slides into the groove — assemble three sides, slide in the bottom, then close with the last side.
Drawer boxes are unforgiving: a sixteenth of an inch too wide and the drawer will not go in. This turns your opening size into the exact box dimensions for your slide type.
Side-mount slides need a specific clearance on each side of the box — typically 1/2 inch, so the box is a full inch narrower than the opening. Undermount slides instead need clearance underneath and a precise box width relative to the opening. The tool subtracts the right clearance for the slide type you choose, so the box comes out to the size the hardware actually expects.
Example
A 24-inch-wide opening with standard side-mount slides needs a box exactly 23 inches wide — half an inch of clearance on each side.
Standard side-mount slides need 1/2 inch on each side, so the box is 1 inch narrower than the opening. Undermount slides have different requirements — check the specific hardware.
Measure the cabinet opening, not the drawer front, and take the width at the front and the back — old cabinets are rarely perfectly parallel. Use the smaller number.
1/2-inch plywood is the usual choice for the sides — strong, stable, and light. Solid wood is lovely but moves with humidity, which is exactly what a drawer that must slide freely does not want.