Quick answer
Choose drawer-slide length from the usable cabinet depth and the slide system’s drawer-box requirements—not from the drawer front. A nominal slide must fit behind the closed front while leaving the front setback, rear-bracket space, obstructions and installation tolerance required by that exact model.
Side-mount and undermount slides do not use one universal sizing rule. Measure the cabinet and drawer, identify the mounting system, then follow its current product specifications and installation sheet. Berta currently lists an 8-inch standard-close side-mount slide, 12–24-inch soft-close side-mount slides, and 12-, 15-, 18- and 21-inch soft-close undermount slides.
Measure in this order
Berta’s drawer-slide type primer helps choose between side-mount and undermount systems. For an existing cabinet, use the replacement slide compatibility checklist before ordering.
Berta drawer-slide lengths by system
| System | Current listed lengths | Good starting use | Must be checked |
|---|---|---|---|
| 8-in. full-extension side-mount | 8 in. | Compact furniture, vanity, desk and specialty drawers | Actual mounting depth, side clearance, rear support and standard-close behavior |
| Soft-close full-extension side-mount | 12, 14, 16, 18, 20, 22, 24 in. | Cabinets and furniture needing common even-inch choices | Usable depth, drawer-side clearance, front/rear mounting and bracket placement |
| Soft-close concealed undermount | 12, 15, 18, 21 in. | Cabinet drawers where concealed hardware and soft close are priorities | Drawer width, side thickness, bottom recess, rear preparation, locking devices and brackets |
These are current Berta Store size families checked October 11, 2026. They are not universal industry size ranges. Confirm the live product page and installation information for the exact model.
Side-mount and undermount boxes are not interchangeable
Side-mount
The rails sit between the drawer sides and cabinet. Nominal rail thickness is not a complete clearance specification; the actual installed pair and manufacturer instructions control box width.
Undermount
The slides sit below the drawer and connect through locking devices. The box must be built around the system’s bottom recess, rear preparation, width relationship and attachment details.
Face frame
Rear brackets can create a different effective depth from a frameless cabinet. Measure to the hardware’s installed position, not just to the cabinet back.
The full-extension undermount explanation covers concealed-slide behavior, while the undermount installation measurements resource should be reviewed for the selected Berta model.
Use cabinet depth as a constraint, not a label
| Scenario | Initial candidate | Why it is only a candidate | Next check |
|---|---|---|---|
| Very shallow furniture drawer | 8-in. side-mount | Compact nominal length may fit where standard cabinet slides do not. | Confirm clear depth, side clearance, drawer box and closing style. |
| Cabinet with about 18 in. of usable depth | 18-in. side-mount or undermount | Both families list 18 in., but their box construction and mounting are different. | Choose system first; then verify setbacks, brackets and drawer requirements. |
| Deep frameless base cabinet | 20-, 22- or 24-in. side-mount | The deepest rail may interfere with the cabinet back or rear hardware. | Measure the closed-front mounting plane to the rear limit and follow the model sheet. |
| Concealed soft-close drawer | 12-, 15-, 18- or 21-in. undermount | Length must correspond to a compatible drawer depth and preparation. | Build a sample box or verify every box dimension before production. |
For drawer material selection, the drawer-box plywood thickness chart explains how material and hardware interact. Do not change drawer-side thickness without rechecking the slide system’s box-width requirements.
Choose the system, then the length
8-in. standard-close side-mount
This compact full-extension ball-bearing slide is listed as 8 inches long and 1/2 inch thick with a 1.8-inch profile. It is standard-close, not soft-close. The 10-pair set lists screws and face-frame brackets. Confirm actual side clearance and rear support.
Review the 8-in. slide
12–24-in. soft-close side-mount
The current family lists 12, 14, 16, 18, 20, 22 and 24 inches. It is a full-extension, soft-close, zinc-plated ball-bearing system with a listed 12.7 mm rail thickness and 45 mm profile width. The product page—not those two figures alone—must guide installed clearance.
Compare side-mount lengths
12–21-in. undermount kit
This concealed soft-close family currently lists 12, 15, 18 and 21 inches. The 10-pair kit includes matching locking devices, rear brackets and screws. The drawer must be made for this undermount geometry; do not substitute side-mount box dimensions.
Compare undermount lengthsSee the full drawer-slide collection or browse other cabinet hardware categories after the cabinet and drawer measurements are documented.
Common drawer-slide sizing mistakes
- Measuring the drawer front. Applied and inset fronts can extend beyond the box and do not define rail length.
- Ignoring the mounting plane. Face-frame brackets and setbacks affect usable depth.
- Buying by cabinet depth alone. The drawer box and chosen system must also be compatible.
- Treating listed thickness as universal clearance. Product dimensions are not a substitute for model-specific installation tolerances.
- Changing slide type without redesigning the drawer. Undermount conversion often requires a different box width, bottom position and rear preparation.
- Building every box before testing one. A verified sample catches dimension and hardware errors before they multiply.
Drawer-slide length questions
Should drawer slides be the same length as the drawer box?
Often the nominal lengths are coordinated, but the exact relationship depends on the model and box construction. Follow the selected slide’s drawer-depth and rear-preparation requirements rather than applying one universal rule.
Can I use a shorter slide in a deeper cabinet?
Sometimes, provided the drawer, mounting, support and desired access work with that system. A shorter slide can reduce usable drawer depth and may require different rear mounting. Verify the complete installation.
How do I choose between an 18-inch side-mount and 18-inch undermount slide?
Choose by drawer construction, appearance, clearances, mounting and performance—not length alone. The side-mount rail sits beside the box; the undermount system needs compatible bottom and rear preparation plus locking devices.
Will a 24-inch slide fit a 24-inch-deep cabinet?
Not automatically. Nominal cabinet depth is not the same as clear mounting depth. Measure from the actual front mounting plane to the rear limit and include all required setbacks, brackets and obstructions.
Are drawer-slide load ratings the same at every length?
Do not assume so. Ratings depend on the exact product, installation, fasteners, drawer construction, extension and test conditions. Berta’s current side-mount and undermount product pages publish figures for their families, but correct installation remains part of the rating.
Installation dimensions remain model-specific
The checked product pages establish current size families, included components and broad product specifications. They do not establish every front setback, rear gap, drawer-width deduction, bottom recess or notch dimension in this article. The final installer should use the current instructions for the exact model and verify a sample drawer before production.
