Installation Length vs Extension Length: Drawer Runner Terminology

The installation length denotes the exact depth dimension of a closed drawer runner required for mounting inside the cabinet. In contrast, the extension length defines the distance by which the runner extends past the edge of the furniture unit when opened. Both values fundamentally determine the usability of the drawer system.

What Do Installation Length and Extension Length Mean Exactly?

For the designer or installer, these two dimensions are the most important parameters when planning a drawer box. The installation length (often referred to in the industry as the nominal length) corresponds to the overall length of the guide rail when completely retracted. During design, it must always be less than the internal cabinet depth to avoid collisions with the rear panel of the unit.

The extension length describes the linear distance the drawer travels out of the furniture. It is directly linked to the construction type of the runner and the number of its profiles. The principle resembles a workshop telescopic rod: the dimension when pushed together is the installation length, whilst the maximum extended distance corresponds to the extension length.

Dependence on Runner Type: Full Extension vs Single Extension

The relationship between installation length and extension length depends significantly on the chosen runner type. Here, a strict distinction is made between two variants:

• Full extension: In this design, the extension length is virtually identical to the installation length. The drawer can be pulled 100% out of the cabinet, allowing the entire interior to be viewed from above. This is achieved using three-part profiles. Full extension drawer runners are the standard in modern furniture construction.
• Single extension: Here, the extension length is significantly shorter than the installation length. Due to their design, these systems can usually only be opened to around 75%. Part of the drawer remains inside the cabinet. Typical examples of this design are simple roller runner drawer slides.

Typical Dimensions and Standards in Furniture Construction

Industrial runner systems are generally graded in 50 mm increments. Standard installation lengths on the market cover the range from 250 mm - 800 mm. The choice of length dictates the depth of the drawer box to be built.

• Short extensions: For narrow bathroom furniture or small bedside tables, compact variants such as 250 mm drawer runners or 300 mm drawer runners are used.
• Standard dimensions: In classic kitchen base units or office pedestals, the standard is usually 500 mm drawer runners or 550 mm drawer runners.
• Extra-long extensions: For deep workshop cupboards or under-platform structures, dimensions such as 700 mm drawer runners or 800 mm drawer runners are used.

Because large extension lengths create immense leverage on the profiles, deep drawers often require the use of specialist heavy-duty drawer runners featuring a load capacity from 45 kg to over 100 kg.

Application & Selection: How to Determine the Correct Dimension?

Technical selection always begins with the exact measurement of the internal cabinet depth. The installation length of the runner must strictly be shorter than this dimension. As a rule of thumb in joinery: internal cabinet depth minus 3 mm to 5 mm tolerance gives the maximum installation length.

Irrespective of the length dimensions, runners can be equipped with various motion mechanisms. These mechanisms do not affect the installation length, but serve contrasting functions:

• Soft-close drawer runners (also called soft-close) brake the drawer as it closes and pull it gently shut. A mechanical alternative without damping cylinders are self-closing drawer runners.
• Push to open drawer runners push the drawer open when pressure is applied to the front. This mechanism is designed for handleless fronts and is the exact opposite of soft-close damping.

Related Terms

• Over-extension: A special runner type whose extension length is greater than the installation length thanks to an additional profile.
• Ball bearing runner: A guide system using steel balls in a ball cage, allowing high load capacities at full extension length.
• Undermount runner: A concealed runner mounted beneath the drawer base. Here too, the installation length and cabinet depth must be matched precisely.
• System 32: A standardised row-of-holes grid with 32 mm spacing, used when mounting the installation length to the cabinet side panel.