A drawer that is a fraction too wide sticks, and one that is too short wastes the space you built the cabinet for. Enter your cabinet opening and clearances below to get the exact drawer box size and a ready-to-cut parts list — front, back, sides and bottom — before you cut a single board.
Your cabinet opening
How the math works
The box has to be smaller than the opening in every direction — room for the slides on the sides, room to lift and slide at the top, and room at the back so the drawer closes fully. The formulas are:
Box width = opening width − slide clearance | Box height = opening height − vertical clearance | Box depth = opening depth − rear clearance
Front/back length = box width − 2 × material thickness | Sides length = box depth | Bottom = (box width − 2 × thickness) × (box depth − 2 × thickness)
Worked example: an opening 18″ W × 8″ H × 20″ D, with 1″ total slide clearance (½″ per side), ½″ vertical clearance, 1″ rear clearance and ½″ material gives a box of 17″ × 7.5″ × 19″. The cut list is: front/back 16″ × 7.5″ (2 pieces), sides 19″ × 7.5″ (2 pieces), and bottom 16″ × 18″ (1 piece). Interior volume is 17 × 7.5 × 19 = 2,422.5 cubic inches.
Tips before you cut
- Measure the real opening, not the plan. Cabinets are rarely perfectly square — measure width at the front and back and use the smaller number.
- Check your slide spec sheet. Most side-mount slides need ½″ per side (1″ total), but some need ⅝″. Enter your slide’s actual number above, not a guess.
- Leave the height alone. A drawer that is too tall binds on the frame above it; the ½″ vertical clearance in the defaults is a safe starting point for most cabinets.
- Pick the right joinery. Our woodworking joinery guide shows which joints hold a drawer box together for years — dovetails for the front, simple rabbets or dadoes elsewhere.
- Check your sheet size first. If you are cutting the bottom from plywood, the plywood sheet calculator tells you how many sheets you need.
Frequently asked questions
What is the difference between side-mount and undermount drawer slide clearance?
Side-mount slides sit between the drawer side and the cabinet and typically need ½″ of clearance per side (1″ total). Undermount slides mount underneath the drawer, so the box can be nearly as wide as the opening — usually only about ¼″ total clearance — but they need a specific drawer-bottom thickness and a notch at the back, so check the manufacturer’s spec sheet before you cut.
How deep should a drawer box be?
As a rule the box depth is the opening depth minus about 1″ of rear clearance, so the drawer can close fully without hitting the cabinet back. It should also match your slide length: a 20″ deep opening with 18″ slides wants an 18–19″ box. A box much shorter than its slides wastes storage; a box longer than its slides will not close.
What thickness should I use for drawer sides?
½″ is the standard for most drawers — strong enough for everyday use and light enough to slide well. Use ⅝″ or ¾″ for wide, heavy drawers (tool chests, pots and pans), and ⅜″ only for small, light drawers such as jewellery or desk trays. Thicker sides eat into interior width, so enter your real thickness in the calculator.
Should the drawer bottom sit in a groove or just be nailed on?
A groove (dado) is stronger and keeps the bottom flat: cut a ¼″ groove about ¼″ up from the bottom edge of all four parts and slide the bottom in during glue-up. A nailed-on bottom is quicker but sags under weight and can pop off when the drawer is loaded. For any drawer that will hold real weight, groove it.