Installation Length vs. Nominal Length (NL) for Drawer Runners — Definition & Measuring Guide

September 16, 2025

The nominal length (NL) describes the standardised length of a drawer runner in its closed state as specified by the manufacturer. The installation length (or clear internal cabinet depth) is the actual space required inside the furniture carcass, which must always be a few millimetres greater than the nominal length to guarantee smooth fitting and function.

What is the exact difference between nominal length and installation length?

When planning and constructing furniture with drawers, exact measurements in millimetres are essential. The nominal length (often abbreviated as NL) is the physical dimension of the fitting itself. It conforms to industrial standards and is usually specified in increments of 50 mm.

The installation length, on the other hand, refers to the spatial requirements of the furniture piece. It corresponds to the clear depth of the carcass, measured from the front edge of the cabinet to the back panel. The nominal length is the precise measurement of the component, comparable to shoe size, whilst the installation length is the space inside the shoe box – it must always provide a little clearance so that nothing collides. If the runner were exactly as long as the clear cabinet depth, tolerances or protruding components on the back panel would often prevent the drawer from closing completely.

Dimensions, standards, and typical values

Drawer runners are available in a wide range of standardised lengths. The sizing grid typically begins for compact furniture at drawer runners 250 mm and ranges across standard dimensions such as drawer runners 500 mm up to extra-long models such as drawer runners 800 mm for deep workshop units or platforms.

To calculate the correct lengths, apply the following technical rule of thumb:

Clear cabinet depth (installation length) = Nominal length (NL) + 3 mm to 5 mm tolerance.
For certain systems such as undermount runners with rear locking hooks, this allowance can also be up to 10 mm. The precise allowances should be taken from the manufacturer's technical drawings.

Effects of extension type and mechanism

The choice of nominal length directly influences how far the drawer can be opened. This depends on the extension type:

Full extension: With drawer runners full extension, the drawer can be pulled out to 100% of the nominal length. A runner with an NL of 500 mm therefore offers an extension travel of 500 mm.
Single extension: Here, the extension travel is only around 75% of the nominal length due to the design. Part of the drawer remains inside the cabinet.
Heavy duty runners: Drawer runners heavy duty often feature a wider and thicker profile to support high load ratings (e.g. 45 kg). The length logic (NL) remains identical, although the installation dimension changes in width (internal carcass width).

Integrated convenience features do not generally alter the nominal dimension of the runner either, but they do demand precision during installation. A soft-close mechanism (drawer runners with soft close) gently decelerates the drawer over the final few centimetres. A completely contrasting system is push-to-open (drawer runners push to open), where the handleless front is opened by pressing. For the trigger travel of push-to-open systems, a front gap of approx. 2 mm to 3 mm must strictly be factored into the installation length.

Measuring guide: How to determine the correct runner length

To identify the correct hardware length when building or replacing, proceed as follows:

Measure clear cabinet depth: Using a folding rule or tape measure, measure the inside of the carcass from the front edge to the inner back panel.
Subtract tolerance: Deduct at least 3 mm from this dimension.
Select nominal length: Round the result down to the next smaller standardised nominal length.

Example: The clear cabinet depth is 465 mm. Subtracting tolerance leaves 462 mm. The correct choice is drawer runners 450 mm.

Check drawer box length: The outer depth of the wooden drawer box (excluding the front panel) corresponds exactly to the nominal length of the runner on most systems.