Doors & Drawers
Drawer Slide Length Calculator
Measure your cabinet once and instantly get the right standard slide length and drawer box depth — whether you're using side-mounts or tricky under-mounts. This tool automatically handles standard sizing increments, factors in inset face thicknesses, and preserves your rear clearance.
Drawer Dimensions
Calculation Results
Max Slide Length to Buy
Build Drawer Box Depth To
Leaves 1.5" of clearance behind the drawer box.
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How slide lengths are calculated
Drawer slides only come in standard increments, and the type of drawer face you are building fundamentally changes how much space you have inside the cabinet. The calculator works backwards from your interior depth to find the largest standard slide that will safely fit without hitting the back panel.
Usable Depth Formula
The first step is determining how much space you actually have to mount a slide. If your drawer fronts sit inside the cabinet (inset), they consume space.
Usable Depth (Overlay) = Interior Depth
Usable Depth (Inset) = Interior Depth − Face Thickness
Example: 22.5" cabinet with a 3/4" inset face → 21.75" of usable depth.Example: 570mm cabinet with a 19mm inset face → 551mm of usable depth.
Max Slide Length
Subtract a safe rear clearance (usually 1/2"15mm) from your usable depth. Then, snap down to the nearest standard slide length that fits.
Max Allowable = Usable Depth − Clearance
Buy Length = Round Down(Max Allowable)
Example: 21.75" usable depth − 0.5" clearance = 21.25". The closest slide size under 21.25" is 21".Example: 551mm usable depth − 15mm clearance = 536mm. The closest standard slide is 500mm.
Standard drawer slide specifications
General jobsite constants for building drawer boxes. Under-mount slides (like Blum Tandem) have strict dimensional requirements for the drawer box. Always confirm the exact deductions and clearances with your specific slide manufacturer's datasheet.
| Under-mount Spec | Typical value | Notes |
|---|---|---|
| Box outside depth | Matches nominal slide length | A 21"500mm slide requires exactly a 21"500mm outside box depth. |
| Box outside width | Opening − 3/8"10 mm | Assumes 5/8"16mm thick drawer sides. Check manual if using 1/2"13mm sides. |
| Bottom recess | 1/2" (13 mm)13 mm | Required space under the drawer bottom for the slide mechanism. |
| Max side thickness | 5/8" (16 mm)16 mm | If using 3/4"19mm material, you must rout the outside bottom edge. |
| Side-mount Spec | Typical value | Notes |
|---|---|---|
| Box outside depth | Matches nominal slide length | Can be shorter than the slide, but matching gives full extension. |
| Side clearance | 1/2"12.7 mm per side | Box width must be exactly 1"25.4mm smaller than the cabinet opening. |
| Box material | Any thickness | 1/2", 5/8", or 3/4"12mm, 15mm, or 18mm sides all work without routing. |
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Frequently Asked Questions
How do I measure for drawer slides?
Measure the interior cabinet depth from the inside edge of the face frame (or front edge of a frameless cabinet) all the way to the back panel. If you are using inset drawer faces, subtract the face thickness from your usable interior depth.
What is the difference in measuring for under-mount vs side-mount slides?
Under-mount slides (like Blum Tandem) require your drawer box to exactly match the nominal slide length. For example, a 21"500mm under-mount slide requires a 21"500mm deep wooden drawer box. Side-mount ball-bearing slides are more forgiving and can be paired with slightly shorter drawer boxes if necessary.
How much rear clearance is needed behind a drawer slide?
It is best practice to leave at least 1/2"15mm of clearance between the back of the drawer slide and the cabinet back panel. This prevents the drawer from crashing into the back and leaves room for standard variances or obstructions like electrical wires and plumbing.
How much narrower should the drawer box be than the cabinet opening?
Standard side-mount ball-bearing slides require the drawer box to be exactly 1"25.4mm narrower than the cabinet opening (1/2"12.7mm clearance per side). Under-mount slides have more complex width deductions that depend on your drawer side material thickness—always check the manufacturer's spec sheet for under-mount width deductions.
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