Nominal Length (NL) vs Extension Length: Drawer Runner Terminology

October 18, 2025

The nominal length (NL) of a drawer runner denotes the exact installation dimension of the closed runner within the cabinet carcass. The extension length, on the other hand, defines the distance the runner travels beyond the front edge of the carcass when open. With a full-extension runner, nominal length and extension length are practically identical, whereas with a partial-extension runner, the extension length is shorter.

What do nominal length and extension length mean precisely?

In the construction of cabinet furniture, precise length measurements are essential for the smooth operation of drawers. The nominal length (often abbreviated as NL) is the static basic measurement of the drawer runners in their retracted state. It determines the minimum depth the carcass must have in order to accommodate the mechanism.

The extension length describes the dynamic travel. Much like a telescopic tube whose closed size corresponds to the nominal length, the extension length indicates how far the inner profile can move forward. The difference between the two values determines the accessible space inside the drawer.

The relationship across different extension types

The technical interaction between nominal length and extension length depends directly on the chosen runner type:

Full extension: Here, the extension length corresponds to 100 % of the nominal length. The drawer can be pulled completely out of the carcass, granting access right to the rearmost corner. Typical designs utilise three-part telescopic runners for this purpose.
Partial extension: With this variant, the extension length is only around 75 % of the nominal length. A section of the drawer remains inside the carcass. This construction is frequently found in classic drawer runners roller guides.

Typical measurements and standards in furniture assembly

The industry manufactures runner systems in standardised increments, usually in steps of 50 mm. The correct selection depends on the planned drawer depth.

Short runners: For bathroom furniture or narrow consoles, dimensions such as drawer runners 250 mm or drawer runners 300 mm are often used.
Standard dimensions: In kitchen and office furniture manufacturing, lengths between 450 mm and 550 mm are the standard. Popular sizes for standard carcasses (depth 560 mm) are drawer runners 500 mm.
Extra-long lengths: For deep workshop cupboards or platform units, the spectrum ranges from 600 mm up to drawer runners 800 mm. In these cases, heavy-duty drawer runners are often required to structurally withstand the leverage when fully extended (observe load capacity in kg).

Usage and selecting the right runner

For installation, one golden rule applies: the nominal length of the runner must always be slightly shorter than the clear internal carcass depth (the inside dimension of the cabinet). A clearance of at least 3 mm to 5 mm to the rear panel prevents the runner from striking the back during fitting.

Furthermore, the mechanism must match the geometry precisely. With soft-close drawer runners, the catch mechanism only engages reliably with the damper cylinder when the nominal length is matched precisely to the drawer depth. Important for planning: a soft-close system pulls the drawer shut gently, whereas push-to-open drawer runners (tip-on) function in the exact opposite manner and eject the drawer by pressing against the front. The two systems cannot be mechanically combined in a single runner.

Related terminology in cabinet making

Clear carcass depth: The exact internal dimension of the furniture unit from the front edge to the rear panel.
Installation width: The lateral space required between the drawer side and the internal carcass wall (often exactly 12.7 mm for ball-bearing runners).
System 32: A standardised hole pattern system in the furniture industry with a 32 mm drilling pitch, to which the fixing points of the runners are aligned.