Determining the right size drawer slides can be tricky the first time – especially if you want the drawer slides ready to go as your building and not hold up your project. Here are simple methods for calculating your drawer slide lengths for overmount and flush mount drawers.

Project Considerations and Measurements You’ll Need

#01: Determine if your cabinet will have a back panel. Usually a 1/4-inch piece.

#02: Make the decision to use under-mount drawer slides (I’ll show you a super-easy way to install them) – at least this build is for an undermount drawer application.

#03: Calculate the thickness of the following material you’re building with: Rear support brace + cabinet backer + drawer slide support piece + face frame. I typically use 1/2-inch material for the drawer slide support piece.

For Overmount Drawers

Calculate your drawer slide length by adding the width of the rear support brace + cabinet backer + drawer support piece + 1/8-inch. Subtract that number from the depth of your project (carcass + face frame). The under-mount drawer slide will rest on the face frame setback about 1/8-inch.

For Flush Mount / Inset Drawers

Calculate your drawer slide length by adding the width of the rear support brace + cabinet backer + drawer support piece + face frame + 1/8 inch. Subtract that number from the depth of your carcass. Do not include the face frame because the undermount slide will mount slightly inside from the face frame (not on the face frame).

Our Hall Closet Project As An Example

Our closet depth was 24 inches and we chose overmount drawers. The rear support brace (3/4 inch) + cabinet backer (0 inches as not used) + drawer support piece (1/2 inch) + 1/8-inch setback from face frame equaled 1-3/8 inches. Subtracted from project depth was 22-5/8 inches. The closest drawer slide length that was less than our available depth was 21 inches. We bought 4 sets of undermount 21-inch Blum drawer slides.

Now it’s time to Install the Drawer Slides!