Belfast Sink Worktop Overhang: 10mm, and Where It Goes

The short answer on Belfast sink worktop overhang is 10mm, and it goes on three sides only. The worktop should lip over the back and both sides of the bowl by about 10mm so water runs into the sink instead of down the outside of the ceramic and into your base unit. The front is different: the front wall of the sink is meant to stand proud of the worktop edge, not tuck under it.

That asymmetry is the bit that catches out first-time fitters, and it is not a stylistic choice. It comes straight off the manufacturer’s own fitting sheet.

The manufacturer’s numbers

Rangemaster’s Belfast fitting instructions, the ones that ship in the box with a fireclay Belfast for solid wood worktops, give three figures worth writing on the back of your hand:

• Overhang: approximately 10mm on the back and the sides of the bowl.
• Front: the cut-out depth should let the front wall of the sink project out by half the depth of the sink wall thickness. On a typical fireclay Belfast with a wall around 20mm thick, that means roughly 10mm of ceramic standing proud of the worktop’s front edge.
• Clearance: try to leave 5mm around the sink once everything is offered up, so the wood can move without pressing on the ceramic.

The marking method follows from that. You take the internal measurements of the bowl, measure 10mm out from each of them, and that is your cut line on the underside of the worktop. Working from the internal dimension rather than the external one is what produces the overhang automatically, and it sidesteps the fact that fireclay sinks are hand-finished and vary. Rangemaster says as much in the same document: because of dimensional tolerances in all ceramic sinks, the instructions are guidelines and you should check against the sink in front of you, not a catalogue figure.

The other line worth reading twice: if the worktop is granite or marble, a fabricator cuts the hole, not you. A jigsaw or router is for solid timber and laminate.

Why the front edge sticks out

Three reasons, and they all matter more than they sound.

Water. A Belfast bowl gets splashed at the front more than anywhere else. If the timber overhangs the front lip, every splash runs back under the worktop, sits on unsealed end grain and stays there. Overhanging timber at the front is the single most common cause of a black, swollen worktop edge two winters after a smart kitchen fit.

Cleaning. A proud ceramic front means you wipe crumbs and water straight off the worktop into the bowl. A recessed one means you wipe them into a 10mm ledge you cannot reach.

Fitting tolerance. Ceramic is not straight. A hand-glazed fireclay front face can wander a couple of millimetres across 595mm. If you try to make the timber sit flush with it, every wobble shows as a gap. Let the sink stand proud and the eye reads it as a deliberate step, not a bad joint.

The dimensions you are fitting around

A standard single-bowl Belfast is roughly 595mm wide, 455mm front to back and 250 to 255mm deep, designed to drop into a 600mm base unit. Common listed sizes are 595 x 455 x 254mm and 595 x 455 x 250mm. That external width leaves almost nothing spare in a 600mm carcase, which is why the base unit under a Belfast is usually a purpose-built sink unit with the back and part of the front removed, or a bespoke frame.

The height is the number that reorganises a kitchen. A 255mm-deep sink hung from the underside of a 900mm worktop leaves only about 615mm of usable cupboard below it, and the waste and trap eat into that too. Plan the base unit around the sink, not the other way round. Our Belfast sink buying guide covers the bowl sizes and the double-bowl options; kitchen base units and kitchen cabinet sizes cover the carcase side.

While you are here: a Belfast has a weir overflow slot at the back of the bowl, a traditional butler’s sink does not. That slot changes nothing about the overhang, but it does change your waste kit, so check which one you actually bought before ordering parts. See sink waste traps.

Supporting the sink, and the silicone

The worktop overhang is not structural, and this is the second thing people get wrong. A fireclay Belfast sits on the base unit or on its own rails and carries its own weight, plus the weight of the water. Fill a 595mm Belfast to the weir and you are holding roughly 30 litres, so around 30kg of water on top of a sink that already weighs 30 to 40kg dry. That load goes into the cabinet or the frame. The 10mm of timber above it is a water deflector.

Rangemaster’s sequence is worth following exactly:

1. Offer up the sink, waste kit and trap together and check they all fit inside your cut-out before you commit.
2. Fit the rails and worktop supports once you are happy with the sink position and the waste position.
3. Lift the sink out, run a bead of silicone on the base unit and on the underside of the worktop overhang, then set the sink back and leave it to go off.

That second bead is the one people skip. It is not sealing a gap for appearance; it is bedding the top rim of the ceramic against the timber so the two are not tapping against each other every time someone leans on the worktop.

Use a translucent silicone, not a coloured one, and do not fill the 5mm expansion gap solid with adhesive. Timber moves across its width with the seasons and ceramic does not move at all. Something has to give, and if it is glued rigid it will be the glaze or the worktop.

Solid timber: seal the cut before the sink goes near it

Every face you cut is raw end grain, and end grain drinks water at many times the rate of a flat surface. On an oak or iroko top, oil the cut-out edges, the underside of the overhang and 50mm back from them, and do it before the sink goes in. Two or three coats, each one allowed to soak in and be wiped back. Then re-oil the front edge and the sink surround every few months for the first year.

A drainage groove set is worth adding on the draining side while the top is out and accessible, and Worktop Express reaches the same 7 to 10mm overhang figure from the timber supplier’s side of the job. Straight grooves are the usual choice in a country kitchen; fan and fountain patterns exist and read as fussier. The groove has to run towards the bowl, which sounds obvious until someone routs them level.

For a painted or laminate top, seal the cut edges with the manufacturer’s sealant or a colourless silicone rather than oil. The failure mode is identical: water gets into the core through a cut edge nobody sealed.

Taps, and the reason wall-mounted ones are common here

A Belfast has no tap ledge. The tap goes either through the worktop behind the sink or on the wall above it.

If it goes through the worktop, remember that the bowl has already eaten 455mm of a 600mm-deep top and your 10mm overhang has taken another 10mm off the space behind it. You are drilling into a strip of timber perhaps 100 to 130mm wide, and the tap needs a spout long enough to reach past the back wall of the bowl and over the drain. Check the spout projection against your actual layout before buying.

Wall-mounted bridge taps sidestep both problems and suit the period look, at the cost of chasing pipes into the wall. That decision is much cheaper to make before the plaster goes on. Our farmhouse and country kitchen ideas page has more on how the two look in practice.

The mistakes worth avoiding

• Marking the cut from the sink’s outside dimension. You get a flush fit with no overhang and water down the cabinet.
• Overhanging the front. Looks tidy on day one, rots the front edge by year two.
• Cutting tight with no expansion gap. A solid timber top pushing against fireclay will crack the worktop or chip the glaze.
• Relying on the worktop to hold the sink. It cannot, and the silicone joint will fail as it tries.
• Oiling after fitting. You can no longer reach the edges that matter most.
• Cutting stone yourself. Belfast cut-outs in granite and quartz are a fabricator job, measured from your actual sink.

Frequently asked questions

How much worktop overhang should a Belfast sink have? About 10mm on the back and both sides. Mark the cut-out by taking the internal dimensions of the bowl and measuring 10mm outwards from them, which produces the overhang without any further arithmetic.

Should the worktop overhang the front of a Belfast sink? No. The front wall of the sink should project out past the worktop by roughly half its wall thickness, which is around 10mm on a typical fireclay Belfast. Timber overhanging the front traps splashes against unsealed end grain.

How much clearance should I leave around the sink? About 5mm once the sink, waste and trap are offered up together. That gap lets a solid timber worktop expand and contract without bearing on the ceramic.

Does the worktop hold the Belfast sink up? No. The sink is supported by the base unit or its own rails and carries its own weight plus the water, which can be 60kg or more when full. The overhang and its silicone bead only deflect water and stop the rim tapping against the underside of the top.

Can I cut a Belfast sink hole in a granite or quartz worktop myself? No. Stone and engineered stone tops have to be templated and cut by a fabricator. Only solid timber and laminate are a jigsaw or router job at home.

Do I need to seal the cut edges of a wooden worktop? Yes, and before the sink goes in. Oil the cut-out edges, the underside of the overhang and the area around them with two or three coats, then keep re-oiling the sink surround for the first year. The cut edges are end grain and absorb water far faster than the face.