Kitchen Sink Cut-Out Dimensions — How to Measure and Allow

A stainless deck with a hob let into it, a stainless shelf above, stemware hanging from a rail at the left and a timber section at the top right. — Everything on this deck sits where it was set out from a datum: hob, shelf and rail. Centring a cut-out by eye is how a tap ends up fifteen millimetres off the line.

01The template beats the catalogue

The single most common cause of a sink that does not fit is a cut-out dimension taken from a catalogue or a website instead of from the bowl that will be installed.

Manufacturers change pressing tools between model years without changing the model code, and a revised bowl can be 4 mm wider than the drawing you have. Two rules follow: get the physical template or the bowl itself, and if neither exists, cut 2 mm small and open it up on site. Opening an aperture is a router job; closing one is a new top.

02Allowance per side, by mounting method

The allowance is the gap between the bowl and the edge of the hole. It is the number that actually has to be right, and it is different for the three mounting methods.

Fig. 1 — Allowance per side. The undermount figure is the one that gets underestimated, because clips need a land, not just a seal.

Those allowances are for the aperture. They are not the clearance to a wall, a hob or another cut-out: leave at least 50 mm of plate between two apertures in a 5–6 mm top, and more in a thinner one.

03Corner radius and the crack that starts there

Every aperture corner concentrates stress, and a sharp internal corner in plate is a crack initiator under thermal cycling. R10 is our minimum, R15 for a top over 2000 mm, and the corner must be a true radius rather than a chamfer.

R0 (sharp) — not offered. It will crack at the corner, eventually.
R10 — the practical minimum for a 5–6 mm top.
R15–R20 — matches most bowls and is easier to seal.
R30+ — only with a bowl that has matching corners; otherwise the plate radius is hidden and pointless.

04Tap holes, centres and the reach problem

Tap holes are drilled after the aperture is cut, from the same datum, which is why they belong on the same drawing rather than in an email two days later.

Tap hole conventions
Fitment	Hole	Centres	Note
Single lever mixer	Ø35 mm	—	Most common; needs 60 mm clear behind
Two-handle pair	2 × Ø30 mm	180–200 mm	Check handle swing against the upstand
Three-hole, mixed	3 × Ø30 mm	200 mm	Middle hole is the spout
Filtered drinking tap	Ø12–16 mm	—	Separate supply; decide before drilling

Then check reach. A tap's spout has to clear the rim of the bowl and land inside it, so a deeper bowl needs a taller tap — and the tap is often chosen before the bowl. A 300 mm deep bowl with a 200 mm reach tap will wet the back edge and nothing else.

05Position from a datum, never from an edge

An aperture dimensioned from the front edge of the top is a dimension that changes when the top is trimmed. Dimension from the back edge and the left edge as datums, and every number survives.

Fig. 2 — The method. Steps one and six are the ones that get skipped and the ones that cause the argument.

We cut to ±0.5 mm from that drawing and record the measured aperture position on the inspection sheet that travels with the top. Our plate is grade 304 or 316L at 5, 6, 8 or 10 mm, and our thickness is checked with a micrometer on arrival, because a nominal 6 mm sheet that arrives at 5.6 mm changes the tolerance the aperture is sitting in. Lead time is 15 working days from a confirmed drawing and packing is on-edge with the rim protected.

If the bowl is ours, we check the drawing against the bowl before the plate is cut. That check costs nothing and it is the one that saves a top. The measured numbers on the inspection sheet are also what we settle a warranty claim against.

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