Hardware math

Drawer slide calculator for side-mount and undermount runners

Drawer slides have one job and one tolerance: the drawer box has to be exactly the right width for the slide brand and slide style. Side-mount runners eat 1/2" per side. Undermount runners need precise reveals and clearance for the underside hardware. Get the math wrong and the drawer either binds or rattles.

The formula

drawer_box_width = cabinet_opening − (2 × slide_clearance)

Slide clearance varies by manufacturer. Most side-mount ball-bearing slides need 1/2" per side (1" total). Most undermount slides need a 5/16" reveal at the front and specific bottom clearance for the runner — check the spec sheet for your slide series.

Example: 12" opening, two slide options

Side-mount ball-bearing slides at 1/2" per side: 12 − 1 = 11" drawer box. Blum Tandem undermount: 12 − (2 × 7/16) = 11-1/8" drawer box, with specific notching at the back for the locking dog. Dead On includes the major brands’ clearance specs so you don’t dig through PDFs at the bench.

Why it matters

Drawer slides are the most return-prone hardware in a cabinet build. Wrong width and you re-rip; wrong depth and the drawer hits the back wall. The math itself is trivial — the difficulty is having every brand’s clearance numbers handy when you cut. A calculator that knows them does that work for you.

Step-by-step

  1. 1

    Measure cabinet opening width

    Inside-to-inside, finish to finish. Account for face frames if present.

  2. 2

    Pick slide brand and model

    Side-mount 1/2" per side is standard. Undermounts vary — Blum, Salice, Accuride all have unique reveals.

  3. 3

    Read drawer box width

    Opening minus 2× clearance. Always round down to the nearest 1/32" to leave a hair of play.

  4. 4

    Read drawer box depth

    Slides come in standard lengths (12", 15", 18", 21"). Drawer box should be 1/2" to 1" shorter than the slide.

  5. 5

    Account for back notching

    Undermounts need a specific notch profile at the back of the drawer. Dead On shows the notch geometry alongside the dimensions.

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Frequently asked questions

What clearance do side-mount slides need?

1/2" per side is industry standard for ball-bearing side-mount runners (Accuride, KV, Hettich). Confirm against the slide’s spec sheet for any high-load or commercial-grade model.

How much clearance for Blum undermount slides?

About 7/16" per side for Tandem and Tandem Plus, plus front and back clearances and a specific back-notch geometry. Dead On has the Blum specs built in.

Does drawer height matter?

Yes for undermount slides — they require a specific height range so the locking dog reaches the back of the drawer. Side-mounts are more forgiving.

How long should drawer boxes be?

Drawer box length should be 1/2" to 1" less than the slide’s nominal length, so the slide can fully extend without the drawer hitting the cabinet back.

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