An undermount sink attaches to the underside of the countertop, and the counter is cut to match that exact sink. There is no rim to cover a rough edge and no slack once the stone is polished, so a sizing mistake here costs real money in a way drop-in shoppers never experience. Getting undermount sink sizes and dimensions right takes a tape measure and fifteen minutes of homework. This guide covers standard size ranges, measuring your cabinet, clearance rules and spec sheet literacy, whether you are renovating a condo kitchen in Vancouver, a bungalow on the Prairies or a century home in Halifax.
Why undermount fit is stricter than drop-in
A drop-in sink forgives small errors because its rim overlaps the cutout and hides it. An undermount reverses that relationship: the cutout edge is visible, finished and polished to follow the bowl. If the sink is too big for the cabinet, or the stone was templated around a different model than the one that arrives on site, the fix is a new sink or a new countertop. Two habits prevent nearly all of this: buy the sink before the countertop is templated, and confirm cabinet fit before you order.
Standard undermount sink size ranges
Exact dimensions vary by brand, from Blanco and Franke composite models to Kohler and Zomodo stainless, but most undermount sinks land in predictable ranges. These are exterior dimensions, the numbers that decide whether the sink fits your cabinet:
| Sink type | Typical exterior width | Typical front to back | Typical bowl depth |
|---|---|---|---|
| Kitchen, single bowl | 23 to 33 in (about 584 to 838 mm) | 17 to 19 in | 8 to 10 in |
| Kitchen, double bowl | 30 to 36 in | 17 to 19 in | 8 to 10 in |
| Prep or bar | 12 to 18 in | 15 to 18 in | 6 to 8 in |
| Bathroom | 16 to 24 in | 12 to 16 in | 5 to 8 in |
Depth deserves its own decision. A 10 inch bowl hides dirty dishes and cuts splashing, but it eats under-sink storage, drops the drain outlet lower against your existing rough-in, and can strain the back of shorter users. An 8 or 9 inch bowl is the comfortable middle ground for most households. If you like the ledge-and-accessory format, workstation sinks follow the same fit rules but often run larger, so check the minimum cabinet line with extra care.
The three numbers on every spec sheet
- Exterior (overall) dimensions. The full outside footprint, including the mounting flange. This is the number that has to clear your cabinet walls.
- Interior (bowl) dimensions. The usable washing area. Two sinks with identical exteriors can have noticeably different bowls depending on material thickness and corner radius, which matters if you want a roasting pan or baking sheet to lie flat.
- Depth. Measured from the rim to the bottom of the bowl. On an undermount, the countertop adds its own thickness above the rim, so the true reach into the sink is a little deeper than the listed figure.
Most manufacturers also publish a minimum base cabinet size. Treat that line as non-negotiable. If the sheet does not list one, a widely used rule of thumb is a cabinet at least 2 to 3 inches wider than the sink's exterior width, which leaves room for mounting clips and the installer's hardware.
How to measure your space
- Measure the cabinet interior width. Tape between the inside faces of the cabinet walls, not across the doors or face frame. Sink base cabinets in Canada commonly come in 30, 33 and 36 inch nominal widths, but interior clearance is what counts.
- Measure front to back. Run the tape from the back of the cabinet to the inside of the face frame, and note how far the plumbing rough-in intrudes into that space.
- Map the obstructions. Water supply lines, the drain stub-out, a garburator where your municipality permits one, and drawer glides in neighbouring cabinets can all steal room the spec sheet assumes is empty.
- Check the counter, not just the cabinet. Confirm there is enough deck behind the cutout for your faucet, soap dispenser or air gap, especially if a full-height backsplash is planned.
Reveal, plumbing and the code question
Your countertop fabricator will ask about reveal, which is how the polished cutout relates to the bowl. A positive reveal leaves a small lip of sink flange visible, a flush or zero reveal aligns the stone exactly with the bowl wall, and a negative reveal overhangs it slightly. None of these is wrong. What matters is that the fabricator templates from the actual sink or the manufacturer's official template, never from a dimension read out over the phone.
On the plumbing side, look for cUPC or CSA certification marks on the sink and any included drain components. The National Plumbing Code of Canada sets the general framework for drainage and venting, but the rules are adopted and enforced provincially and locally, so leave trap and venting decisions to a licensed plumber in your area. A deeper bowl can also lower the drain outlet enough that an existing rough-in needs adjusting, and that is a conversation to have before demolition, not after.
Common fit mistakes
- Measuring the old bowl instead of the exterior. Interior dimensions tell you nothing about cabinet fit. Always compare exterior to cabinet.
- Upsizing a double bowl into a single-bowl cabinet. Double and low-divide sinks often need 33 to 36 inches of cabinet. Wanting two bowls does not create the space for them.
- Ordering the countertop first. The stone is cut to the sink, so the sink must be on site, or at minimum confirmed and templated, before fabrication starts.
- Ignoring countertop material. Undermounts pair with solid materials such as granite, quartz and solid surface. A standard laminate edge is exposed by an undermount cutout, so laminate counters usually call for a drop-in instead.
- Forgetting the drawers. In bathrooms, the bowl and its drain drop into the vanity's top drawer zone. Check that your vanity has a U-shaped top drawer or a false front before committing to a deep bowl.
If you are at the shortlist stage, compare spec sheets across our kitchen sinks collection, which includes undermount models from Blanco, Franke, Kohler, Bosco and Zomodo, or browse compact prep and bar sinks for islands and butler's pantries. Everything ships Canada-wide, and our buying guides hub has companion reading on faucets, drains and countertop pairings.
Frequently asked questions
What size undermount sink fits a 36 inch base cabinet?
Most single and double bowl sinks up to roughly a 33 inch exterior width will fit a 36 inch base, but always defer to the manufacturer's stated minimum cabinet size, since flange design and mounting hardware vary between brands.
Are sink dimensions listed in inches or millimetres in Canada?
Usually both. Canadian spec sheets typically show imperial with metric in brackets, and European brands such as Blanco, Duravit and Villeroy & Boch often lead with millimetres. Pick one unit and use it for every measurement in your project, because rounding back and forth between the two is exactly where cutout errors creep in.
Can I replace a drop-in sink with an undermount without changing the countertop?
Rarely. The existing cutout was sized for a rim to cover it, so its edges are unfinished and usually the wrong shape for the new bowl. In most cases an undermount conversion happens alongside a new countertop, which is also the ideal moment to get sizing right.
How deep should an undermount kitchen sink be?
Bowl depths of 8 to 10 inches are typical. Go deeper if you regularly wash stock pots and baking sheets and have generous plumbing clearance below. Stay shallower if under-sink storage matters or deep bowls feel uncomfortable, and remember the countertop's thickness adds to the effective reach.
