Custom Sink Sizes for Cabinet Manufacturers: A Working Guide

If you build cabinets and bundle a sink with them, the sink is not a product — it is a component. It has to fit a cutout your CNC programme already knows, align with your worktop machining, and arrive at the same tolerance every time.

Standard catalogue sinks rarely fit that requirement exactly. That is why cabinet manufacturers end up specifying custom dimensions, and why the conversation with a sink factory needs to be more precise than a normal purchase order.

The dimension chain, and where it breaks

Every custom sink is defined by a chain: cabinet width → worktop cutout → sink outer dimension → bowl dimension. A change anywhere in that chain propagates.

The chain breaks most often at the outer-to-cutout relationship, because different rim types have different overlaps:

• A topmount rim overlaps the cutout by 15 to 20 mm per side.
• An undermount flange sits under the counter with its own overlap, typically 12 to 18 mm depending on the fixing design.
• A flush mount has minimal overlap and requires the cutout to match the sink edge nearly exactly.

If your factory quotes “800 mm sink” and you cut an 800 mm hole, you have a 30 to 40 mm gap. Always specify both dimensions explicitly, and ask for a dimensioned drawing that shows both.

What you actually need to send the factory

A complete custom specification has six elements. Factories that receive all six produce correct samples on the first attempt; factories that receive three produce something you have to reject.

1. A dimensioned drawing of the sink, showing outer dimension, bowl dimension, bowl depth, drain hole centre position and diameter, rim type, and corner radii.
2. The gauge and grade — for example 304 at 1.2 mm nominal.
3. The rim and fixing design — topmount with rolled rim, undermount with clip brackets, and the bracket positions.
4. The finish — brushed with grain direction, or PVD with a colour reference.
5. The cutout drawing for your worktop, so the factory can confirm the overlap works.
6. The packaging requirement — carton dimensions if you are palletising to a fixed module, and any print artwork.

The sixth item is the one most often forgotten, and it is the one that causes the most expensive delay when it arrives late, because packaging tooling has its own lead time.

Tolerances: what to ask for and what to expect

Custom does not mean infinite precision, and the tolerance you specify determines the price.

For a welded (handmade) sink, achievable tolerances are roughly:

For a pressed sink, the die controls dimensions, so overall tolerances are tighter, but you cannot vary the dimension at all without a new die.

Practical advice: specify ± 2 mm on bowl dimensions and ± 1.5 mm on overall, rather than demanding ± 0.5 mm across the board. The tighter number adds cost and reject rate without improving the installation, because the cutout tolerance in the worktop is almost always looser than the sink tolerance anyway.

One exception: if you are running flush mount, the rim flatness and the overall dimension both need to be tight, because the joint is visible. Do not compromise there.

Sample approval: the step that saves a container

Never approve a custom sink from a drawing and a photo. Approve from a physical sample that you fit into a real cabinet and a real cutout.

The approval should test four things:

Fit. Does it sit in the cutout with the intended overlap on all four sides? Check the diagonal — a sink that is 2 mm out of square will fit one corner and gap the opposite one.

Rim flatness. Put a straight edge across the rim. Any rocking means the sink will not bed down evenly, and a topmount will leak at the high corner.

Drain alignment. Offer the sink into the cutout and check that the drain centre lands where your plumbing rough-in expects it. This is the most common site problem and it is trivially avoidable at sample stage.

Finish match. If you are producing a run of kitchens, compare the sample’s brushed grain against your reference. Batch variation in brushing is real, and a mismatch across a kitchen run is a visible defect.

Approve the sample in writing with the dimensions recorded, and keep it. When a later batch arrives out of spec, the approved sample is your reference.

MOQ and the economics of custom

Custom sizes on welded construction have no tooling, so MOQ is typically modest — a few dozen pieces per size is often workable. That makes custom viable for a cabinet programme even at low volume.

Custom sizes on pressed construction require a die, so MOQ is set by die amortisation, usually in the hundreds or thousands. This is why most custom sink work is welded.

The cost premium for custom welded versus standard welded is typically small — the main drivers are the size itself and the finishing time, not the fact that it is custom. What costs money is deviation from the factory’s existing jigs: unusual corner radii, non-standard drain positions, or a rim design the factory has not built before.

If your requirement is close to a standard size, ask whether a small modification to an existing jig gets you there. It often does, and it is cheaper than a fully bespoke build.

Lead time planning

For a first custom order, plan the sequence as: drawing approval (1 week) → sample production (2 to 3 weeks) → sample transit (3 to 5 days by air) → approval (1 week) → production (25 to 40 days) → sea freight (25 to 40 days depending on destination).

That is roughly 4 to 5 months from specification to stock on the floor. Most cabinet programmes underestimate this, then pay for air freight on the production run to hit a launch date.

For repeat orders of an approved size, the sequence collapses to production plus freight, so the second order is much faster. The cost of getting the first one right is paid once.

The five mistakes that cause site returns

1. Quoting cutout instead of outer dimension (or vice versa). Confirm which one is on the drawing.
2. Forgetting drain position. A sink that fits but puts the drain where the cabinet’s plumbing cannot reach is a return.
3. Ignoring the tap hole. If your worktop is drilled for the tap, the sink’s rear flange must not interfere with the tap base. Check the rear flange depth.
4. Approving finish from a photo. Brushing direction and reflectivity do not photograph accurately.
5. Skipping the packed-carton test. A custom sink in a standard carton that does not fit properly will arrive damaged, and custom sizes are not replaceable from stock.

Working with the factory as a partner

A cabinet manufacturer buying sinks is a different customer from a distributor. You order fewer SKUs, more consistently, with tighter dimensional requirements and a longer relationship horizon.

That is worth saying explicitly when you approach a factory. A supplier who understands you are building a programme, not testing a market, will allocate sample capacity and hold your jig — and that is worth more than a marginally lower unit price.

Next step

We build custom welded sinks to drawing in 304 and 316, from a few dozen pieces per size, with dimensioned drawings and physical samples before production. If you are aligning a sink to an existing cabinet programme, send us your cutout drawing and cabinet width and we will confirm the rim type and overlap before anything is built.