How to use it
Measure the opening
Measure each drawer opening of the case as built: width, height and depth. Real plywood is rarely its nominal thickness, so measure rather than add up the drawing.
Find your slides' clearances
From the slide maker's instructions for the exact slide you will use: the space it needs at each side, and any setback or space behind the box. Enter the space you want above and below the box too.
Read the box size
The result is the outside of the drawer box. Choose a slide length the maker lists that suits that depth; slides come in fixed lengths.
For a stack, divide the height
Enter the height to divide, the number of drawers, the rail or gap between them and, for graduated drawers, how much taller each is than the one above.
The drawer box
Formula
box width = opening width − left clearance − right clearance
box height = opening height − top clearance − bottom clearance
longest box = opening depth − back clearance
No clearance is universal. Each side-mount slide needs its own side space, and even one maker's page can be unclear: Accuride's guide for its 3832 slide on a frameless cabinet asks for ½ in of side space between box and cabinet and, on the same page, for a box at least 11/16 in narrower than the opening — which would not leave ½ in each side. Use the figure on the data sheet for the slide you buy. Undermount slides go further and set the box's inside width, its side thickness and notches at the back; this calculator does not give those, so follow that slide's own instructions.
Drawer spacing
A stack of N drawers with a rail or gap of d between each fills a height H with N − 1 dividers and no divider above the top or below the bottom. Equal drawers are each (H − (N − 1) d) ÷ N. Graduated drawers grow by a step g from top to bottom, and the top one is (H − (N − 1) d − g N(N − 1) ÷ 2) ÷ N.
Formula
equal: h = (H − (N − 1) × d) ÷ N
graduated: h₁ = (H − (N − 1) × d − g × N(N − 1) ÷ 2) ÷ N
hᵢ = h₁ + (i − 1) × g
H: height to divide; N: number of drawers; d: rail or gap between drawers; g: how much taller each drawer is than the one above.
Worked example: four drawers in 30 in with 3/4 in rails. Equal, each is (30 − 3 × 3/4) ÷ 4 = 6-15/16 in. Graduated by 1 in, the top one is (30 − 2-1/4 − 1 × 4 × 3 ÷ 2) ÷ 4 = 5-7/16 in, then 6-7/16, 7-7/16 and 8-7/16 in — which, with the three rails, add back to 30 in. The step is a design choice; no proportion for graduated drawers is a standard.
Use the same tool for overlay fronts: enter the total height the fronts cover and the gap between fronts. Fronts themselves are sized like doors in the cabinet door size calculator; the box and the front are never the same dimension.
What the result does not include
- The slide's own rules: its length, setback, mounting height and, for undermount slides, the box's inside width and notches.
- The drawer front, which overlaps or sits inside the opening and is sized separately.
- Material thickness. Plywood sold as 1/2 in is often thinner; see the plywood thickness chart.
- Movement. A solid-wood case or drawer side changes size with moisture; see the wood movement calculator.
- Tip-over. A tall chest of drawers or dresser can tip when drawers are opened; the CPSC's standard for clothing storage units covers that, not this arithmetic.
Safety— Chests of drawers can tip
Free-standing clothing storage units that meet the CPSC's size and weight thresholds fall under its tip-over standard, and any tall case should be anchored to the wall. Drawer sizes say nothing about stability. See woodworking safety rules and the order of work in learning furniture making.
Before building drawer boxes
- Each opening measured on the case as built
- Side clearance and setback from the data sheet of the slide you will use
- Top, bottom and back space chosen
- Box and front sized separately
- Material thickness measured, not assumed
Sources
The arithmetic is plain geometry and is tested against hand-worked examples; no clearance is assumed. Accuride's figures are cited as an example of a slide maker setting the clearance — and of a maker's own page giving two figures that disagree, which is why the slide's own data sheet should be checked. Undermount slides set their own box rules and are not modelled. Graduated spacing uses a constant step, a choice the user makes, not a standard proportion.
- 1.
How to Install a 3832 Drawer Slide on a Frameless Cabinet in a Few Steps. Accuride International.
Used for: Why clearances come from the slide: Accuride's installation guide for its 3832 side-mount slide on a frameless cabinet asks for a drawer box with ½ in of side space between it and the cabinet, and also for a box at least 11/16 in narrower than the opening — two figures on one page that do not agree, since ½ in each side would make the box 1 in narrower; it recommends at least 1/8 in setback on the drawer member, while saying the need may vary.
- 2.
Clothing Storage Units (16 CFR part 1261) FAQ. U.S. Consumer Product Safety Commission.
Used for: Free-standing clothing storage units — chests of drawers and dressers — meeting the CPSC's size and weight thresholds fall under its tip-over standard, which drawer sizing does not address.
About this calculator
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.