Full Extension vs Partial Extension — Is the Extra Cost for Drawer Runners Worth It?

A full extension runner opens by 100%, whereas a partial extension runner remains partly within the cabinet carcass and only reveals around 75% of the drawer depth.

When building furniture or retrofitting cabinets, choosing the right runner technology is an essential decision. The choice of drawer slides affects daily access, usable storage space, and the overall ergonomics of the furniture unit. Anyone planning drawers must fully understand the mechanical limitations and installation dimensions of the respective fittings to prevent collisions or insufficient load capacities later on.

What is a partial extension drawer runner?

A partial extension runner is the traditional standard solution in furniture making. With this design, the drawer cannot be pulled completely clear of the cabinet. A section of the drawer box – usually between 80 mm and 100 mm – remains firmly inside the carcass. In technical terms, this is referred to as extension loss.

Technically, this is frequently implemented using simple roller drawer runners, where sliding plastic rollers run within an epoxy-coated metal track. Ball bearing versions also exist for this type. The construction is mechanically simple, making these slides highly robust and rarely prone to faults. They are also forgiving of minor dimensional tolerances when building the wooden cabinet carcass.

What is a full extension drawer runner?

A full extension runner consists of a multi-part telescopic system. Thanks to interlocking steel profiles that glide within one another, the drawer box can be pulled out completely from the carcass. Like a well-organised toolbox that instantly gives a clear view of every tool, this slide provides direct access right into the rearmost corner of the drawer.

Modern full extension drawer runners generally use ball bearing runners (side mounting) or undermount runners (concealed mounting beneath the drawer base). They feature a more complex construction and require precise clearances during installation. For instance, if you fit 500 mm drawer runners, the actual extension travel is precisely 500 mm.

Technical differences in detail

Choosing between the two systems comes down to specific structural and spatial requirements. The following parameters fundamentally distinguish the two designs:

• Extension travel and ergonomics: The most obvious difference. While a partial extension leaves a blind spot at the back, a full extension system provides complete access. This prevents items from disappearing into the rear of the drawer or requiring awkward fumbling to reach.
• Load capacity and leverage: Thanks to their multi-part telescopic construction and ball cages, full extension slides are often rated for significantly higher weights. Heavy duty drawer runners can effortlessly support loads of 30 kg, 45 kg, or even over 100 kg in industrial applications. Partial extension runners reach their structural limits much sooner under heavy loading, as the leverage acting on the front rollers increases sharply when the drawer is opened wide.
• Installation dimensions and tolerances: Side-mounted ball bearing runners typically require precisely 12.7 mm of clearance between the outer drawer side and the inner carcass wall (meaning a total side clearance of 25.4 mm). Here, timber cutting must be millimetre-precise. Roller runners can sometimes cope with slight dimensional variations and are often screwed into place according to standardised System 32 hole spacing (32 mm drilling pitch).
• Convenience features: Both systems can be fitted with additional mechanisms. However, it is essential to distinguish between them clearly. Soft-close (damping) cushions the drawer as it shuts and gently pulls it closed over the final centimetres. Push-to-open (tip-on) is the exact opposite mechanism designed for handleless fronts, where pressing the front mechanically ejects the drawer. Soft-close drawer runners are the absolute technical benchmark for full extension systems, whereas for partial extension runners they are often merely an optional retrofit solution.

Which drawer runner is best suited for each application?

The choice of hardware should always be guided by the intended use, cabinet depth, and the weight of the stored items.

When a partial extension is completely sufficient

For shallow drawers with limited depth where you can see all contents at a glance anyway, a partial extension is a solid choice. Classic examples include small desk pedestals, shallow stationery drawers, or bedside tables. If you are fitting short 300 mm drawer runners, the extension loss of around 75 mm is easily manageable since your hand can comfortably reach the rear panel. Roller runners also show their strengths in projects where quick, forgiving installation is required.

When a full extension is strictly necessary

In kitchens (particularly in pan drawers), in workshops, or in deep wardrobes, the 100-percent solution is indispensable. As soon as large, bulky, or heavy items need to be lifted out vertically from above, full access is an ergonomic necessity.

For deep cabinets requiring 600 mm drawer runners, a partial extension would be impractical. Items in the back quarter would be obscured by the worktop or shelf above and would be nearly impossible to grasp. Furthermore, when using undermount drawer runners in premium furniture making, full extension mechanisms are almost exclusively chosen to combine clean aesthetics with maximum user convenience.

Frequently Asked Questions (FAQ)

Can you simply replace a partial extension with a full extension runner?

Yes, retrofitting is possible in most instances, though it requires precise measurements. The most critical dimension is the side clearance. If the old roller runner used 12.5 mm to 13 mm of space, a standard ball bearing slide will fit neatly into the gap. Pay close attention to the exact nominal length as well. If the original runner measured 400 mm in length, select 400 mm drawer runners in a full extension variant as a replacement.

What does the term over-extension mean?

An over-extension is a specialised variant. With this type, the drawer can be pulled out beyond 100%, extending to roughly 110% of the carcass depth. When fully open, the back of the drawer box actually sits several centimetres in front of the cabinet edge. This is frequently utilised in filing cabinets or specific workshop furniture, allowing tall folders or containers to be lifted straight out without catching on the cabinet frame.

Are there full extension runners that combine push-to-open and soft-close?

In principle, these two mechanisms are mechanically opposed. Push-to-open requires a tensioned spring to push the drawer forwards upon pressing. Soft-close requires a damper to decelerate the drawer and pull it backwards. In the premium segment, highly complex (and installation-heavy) runner systems exist that combine both functions using synchronisation rods. For standard furniture construction, however, one typically opts for either one function or the other. When designing handleless fronts, dedicated push to open drawer runners are the more technically dependable choice.