Drawer slide sizing
Drawer slides look like commodity parts until you spec the wrong one for the load. A 22″-deep kitchen drawer full of cast iron needs a 100 lb slide, not the 45 lb one. This calculator picks the right slide type, length and load rating by drawer dimensions and contents.
Calculator
The four families of drawer slide
Side-mount ball-bearing: the workhorse. Inexpensive, holds up to 100 lb, easy to install. Visible from the side; doesn't matter on a painted cabinet carcass.
Undermount soft-close: the upgrade. Hidden under the drawer, soft-close action, holds up to 100 lb. More expensive, requires a 5/8″ clearance on each side, requires drawer box fabrication to be precise (within 1/32″).
Centre-mount: one slide under the drawer centre. Light-duty only (under 30 lb). Used for small utility drawers in shops.
Wood-on-wood: traditional. Drawer rides on wood runners in a wood frame. Quiet, classic, but no slide action — just a friction fit. Good for shop furniture where a slam-shut is fine.
Sizing the load
Manufacturer load ratings are per pair under ideal conditions (centered load, full slide engagement, smooth action). Real-world conditions are harsher — if the load is concentrated at the front of the drawer when fully extended, the effective rating drops 30%. For tool drawers and kitchen pantry drawers, overspec by 50%.
Limitations
- Doesn't account for drawer box deflection. A 1/2″ plywood bottom on a 24″-wide drawer sags more than 1/2″ plywood on a 16″-wide drawer — affects perception of slide quality, not the rating.
- Doesn't model soft-close dampers — they fail with age and use.
- Doesn't include drawer front attachment — check that your slide-to-drawer box-to-front system is compatible.
- Doesn't predict sag over decades. Slides wear; budget for replacement on heavily-used kitchen drawers.
Frequently asked questions
Are undermount slides worth the money?
For a kitchen or bathroom, yes — soft-close is genuinely nicer, and the hidden slides look better. For shop drawers and utility cabinets, no — a $5 side-mount works as well and is easier to replace when it wears out.
My slide won't close smoothly. What's wrong?
Most common: drawer box is out of square (one side bigger than the other), the cabinet isn't square (slides can't align), or the slide is mounted to a wall that bows in or out. Disassemble, square the drawer box, shim the cabinet. Slides themselves rarely need lubrication.
Why do my slides always sag?
Either the load rating is too low (overspec next time) or the slides are wearing out. Cheap slides have plastic bearings that flatten over years. Replace with a better slide rather than lubricating.