How to Calculate Drawer Dimensions

Start from the opening

Measure the internal width and depth of the carcase opening — never the external size.

Side-mount slides

Each slide occupies roughly 13–15 mm on its side wall:

Box width = internal width − 2 × slide clearance

Under-mount slides

The slide sits under the drawer, so the box width equals the internal width minus a small clearance. Follow the manufacturer datasheet.

Bottom and depth

Side length = internal depth − front thickness (or full depth for an overlay front)
Bottom = (box width − 2 × side thickness) × side length

Practical tips

• The datasheet always wins over generic rules.
• Use 4–6 mm plywood for the bottom.
• Leave 2–3 mm vertical play.

Compute your box with the drawer calculator.