Drawer Slide Clearance Calculator
When building drawers with side-mount ball-bearing slides, the drawer box must be narrower than the cabinet opening by the amount the slides occupy on each side. Most standard 3/4-extension and full-extension slides require 1/2 inch per side. This calculator takes the cabinet opening width, the clearance required per side (from your slide manufacturer specifications), and an additional gap for fit, and returns the correct drawer box width. It also shows the total clearance deducted and remaining side space.
Drawer box width formula
Total deduction = 2 × (clearance per side + fit gap)
Drawer box width = opening width - total deduction
Each side of the drawer box must clear the slide hardware and leave a small operating gap. The total deduction is twice the per-side amount (left and right). Subtracting from the opening width gives the correct drawer box width. Always verify the final dimension against the slide manufacturer's table for the exact slide model you are using.
Drawer box construction tips
- Build drawer boxes from 1/2-inch Baltic birch plywood for a strong, stable, lightweight box that minimises seasonal movement.
- Use a rabbet-and-dado or lock-rabbet joint at the corners for maximum drawer box strength.
- The drawer bottom should float in a groove routed around the inside of the box to allow seasonal movement.
- Test-fit the box in the opening before attaching the drawer face to ensure smooth operation throughout the full travel.
- Adjust the slide mounting height so the drawer box bottom is level with the bottom of the face frame opening.
Drawer slide clearance calculator: frequently asked questions
What clearance do standard side-mount drawer slides require?
Most side-mount drawer slides (such as common ball-bearing slides) require 1/2 inch of clearance per side, meaning the drawer box must be 1 inch narrower than the cabinet opening. Some slides require 3/8 inch per side or 17mm per side for metric European hardware. Always check the manufacturer specification.
Why is the drawer box narrower than the opening?
The slide mechanism occupies space between the drawer box and the cabinet side. Each slide is mounted to the cabinet side and a corresponding member is mounted to the drawer box. The clearance gap is the thickness of the slide hardware, plus a small amount for smooth operation and seasonal wood movement in the cabinet sides.
What clearance do under-mount drawer slides need?
Under-mount slides (such as Blum Tandem or Grass Nova) mount to the bottom of the drawer and the cabinet bottom or bottom rail. The drawer box can be full width of the opening minus a small amount (typically 1/16 to 1/8 inch per side) for the tandem mechanism flanges. Always verify with the specific manufacturer's data sheet.
How tall should the drawer box be?
Drawer box height depends on the intended contents, the face frame or face opening height, and the slide clearance at top and bottom. Standard practice leaves 1/2 to 3/4 inch of clearance between the drawer box top and the face frame rail above it, and about 1/8 inch clearance below the drawer box bottom for the slide mounting.
Does wood movement affect drawer fit over the seasons?
Yes. Wood drawer boxes and wood cabinet sides both move with humidity changes. A perfectly fitting drawer in summer may bind in winter if there is no clearance. The standard 1/2-inch-per-side clearance for metal slides provides ample room for seasonal movement. Plywood drawer boxes move less than solid wood boxes.
Official sources
- USDA Forest Products Laboratory: Wood Handbook, FPL-GTR-190 (wood movement and fastening).
- USDA Forest Service: FPL Homepage.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.