Nominal Length (NL) for Drawer Runners: Definition & Measuring Guide

April 22, 2026

The nominal length (NL) of drawer runners refers to the exact measurement of the fully closed guide rail in millimetres. This value strictly defines the minimum internal depth required for the cabinet carcass and the maximum depth of the drawer box to ensure flawless installation.

What exactly is the nominal length?

In professional furniture making, the nominal length is the most important reference value when planning drawer runner systems. It does not indicate the extension distance, but rather the physical length of the runner in its fully retracted state. The nominal length is the technical backbone of the drawer: if it is chosen too short, valuable storage space inside the carcass is wasted; if it is too long, the runner will hit the back panel and prevent the front from closing flush.

On most systems, the nominal length corresponds exactly to the external depth of the drawer box. A runner with an NL of 500 mm therefore usually requires a drawer box measuring exactly 500 mm from the outer edge of the back panel to the inner face of the drawer front.

Typical dimensions and standards

Drawer runners are manufactured in standardised grids, usually in 50 mm increments. This facilitates series production according to System 32. The range extends from very short runners for bathroom furniture, such as drawer runners 250 mm, up to extremely long variants for deep workshop units. An absolute standard size in kitchen manufacturing is, for example, drawer runners 500 mm.

The internal carcass depth (clear depth) must always be slightly greater than the nominal length of the runner. Depending on the manufacturer and the type of runner (such as ball bearing runners or undermount runners), an allowance of 3 mm to 5 mm must be included. Example: with an NL of 450 mm, the clear carcass depth must be at least 453 mm.

Measuring guide: how to determine the correct nominal length

Whether designing a new piece of furniture or replacing worn-out hardware, determining the correct nominal length is achieved in a few precise steps:

For new construction (planning)

Measure internal carcass depth: Measure the distance from the front edge of the carcass to the inner surface of the back panel.
Deduct tolerance: Subtract 3 mm to 5 mm from this measurement.
Round down: Round the result down to the nearest standard size (in 50 mm increments).

(Example: Measured internal depth 520 mm - 3 mm = 517 mm. The suitable nominal length is 500 mm).

When replacing existing runners

Dismantle runner: Remove the old runner and push it completely closed.
Measure length: Measure the runner from the front edge to the rear edge. This value in millimetres is the nominal length.
Alternative method: Measure the outer depth of the existing wooden drawer box (excluding the front panel).

Impact of nominal length on extension type and mechanics

The nominal length is directly related to the extension travel and the leverage exerted on the runner.

Extension type: A full extension runner can be pulled out of the carcass by 100 % of its nominal length. With an NL of 400 mm, the extension travel is therefore also 400 mm. A single extension (partial extension), by contrast, opens only around 75 % of the nominal length. For full access to all contents, drawer runners full extension are the industry standard.
Convenience features: The nominal length influences the positioning of integrated mechanisms. Systems such as drawer runners with soft close slow down the closing motion over the final centimetres. The opposite mechanism, drawer runners push to open (tip-on), often requires 1 mm to 2 mm of additional activation travel (front gap), which must strictly be considered in the carcass depth.
Load capacity: The longer the nominal length, the higher the leverage force when the drawer is fully extended. For deep and wide units, drawer runners heavy duty capable of handling dynamic loads of 45 kg or more must be installed.