For a 28-inch undermount sink, measure the countertop cutout opening, not the sink’s outer lip — the sink hangs under the counter, so the opening decides the fit.
For the full breakdown, see our best 28-Inch Undermount Kitchen Sink guide.
On a drop-in sink, the rim rests on the counter and the hole underneath doesn’t matter. An undermount flips that: the counter edge is the visible border, and a cutout that runs long leaves exposed cabinet or a gap you cannot hide. Get the opening right and the rest falls in line — overall width, bowl size, depth, drain opening, and the cabinet that has to swallow all of it. Below are the measurements that matter, the template trick installers use before any saw touches stone, and the mistakes that turn a weekend job into a countertop replacement.
What Measurements Actually Decide The Fit?
Five numbers decide whether a 28-inch undermount sink works: cutout length, cutout width, overall sink size, bowl depth, and minimum cabinet width. The cutout and the cabinet fail most often.
Measure the countertop opening left to right for length, then back to front for width, per Home Depot’s sink measuring guide. Measure basin depth from the counter edge straight down to the deepest point of the bowl, not from the rim.
Overall sink dimensions tell you what fits beneath the counter; bowl dimensions tell you whether your largest sheet pan clears the sides. Minimum cabinet width is the spec people skip at the store and discover at home with a saw in hand.
Setting Up The Template Before You Cut
Professional guidance recommends building a plywood template rather than cutting straight from the spec sheet: place the sink upside down on plywood, trace its perimeter, then adjust the outline for the reveal you want. Align the template’s center with the countertop center mark and clamp it down before cutting.
The reveal is the sliver of counter showing around the sink’s edge. An overhang reveal hides the sink edge almost entirely; a positive reveal leaves a thin visible rim of stainless. Each changes the cutout differently, so the template must be built for the reveal you’ve chosen. When a sink ships with its own template, use it — Foster’s installation instructions note that the actual sink or its supplied template gives the most accurate cutout. Foster’s guidance also places the sink roughly 2 to 2½ inches back from the front edge, depending on countertop overhang and sink type.
Confirm the countertop material and fabrication method first. These instructions are for professional installers working with routers and templates, and laminate or solid-surface behaves nothing like quartz or granite.
A Real 28-Inch Sink, By The Numbers
Concrete specs beat vague advice. Here’s what a verified 28-inch undermount single-bowl model lists — a Ruvati 16-gauge stainless sink with a 26.25-inch cutout length and a 33-inch minimum cabinet.
| Specification | Verified Example | Why It Matters |
|---|---|---|
| Overall sink size | 28 in x 18 in | Must fit beneath the counter opening |
| Cutout length | 26.25 in | Defines the counter hole, not the sink lip |
| Cutout width | 17.99 in | Too wide leaves an exposed edge |
| Bowl depth | 9 in | Controls how much fits in the basin |
| Drain opening | 3.5 in | Must match your drain assembly |
| Minimum cabinet | 33 in | Cabinet must be wider than the sink |
| Interior bowl | 26 in x 16 in | The usable washing area |
Notice the gap between 28 inches and 33 inches. Many 28-inch sinks need a cabinet wider than 28 inches, and other models list minimums at 31 inches, so check cabinet width before you order. If you’re comparing models, this tested roundup of the best 28-inch undermount kitchen sinks breaks down specs side by side.
The Mistakes That Cost You A Countertop
Almost every failed installation traces back to five errors, and four happen before the saw comes out.
- Measuring the rim. On an undermount sink, the outer lip is hidden — the cutout opening is the real dimension.
- Ignoring the cutout spec. Overall sink size and cutout size are different numbers, and the cutout is the one being cut.
- Skipping the template and reveal step. A mismatched reveal leaves a visible edge or a gap sealant can’t fix.
- Not checking minimum cabinet width. A 28-inch sink often needs 31 to 33 inches of cabinet interior.
- Overlooking drain diameter. Several 28-inch sinks list a 3.5-inch drain opening — confirm yours matches.
Work through them in order, template first. Ruvati’s product documentation and Home Depot’s measuring guide both list the cutout and cabinet specs for a reason: they’re the two numbers that make or break the fit. Measure the opening twice, build the template, and check the cabinet before the countertop gets touched.
FAQs
Why is the cutout smaller than the sink itself?
Because the sink hangs below the counter, the counter edge has to overlap the sink slightly to support it and hide the rim. A 28-inch sink typically has a cutout around 26 to 26.25 inches, leaving roughly an inch of counter bearing on each side.
Can a 28-inch undermount sink fit a 30-inch cabinet?
Usually not. Verified 28-inch models list minimum cabinet widths of 31 inches and 33 inches, and cabinets are measured on their interior. Confirm your exact cabinet interior before buying, not the exterior width on the box.
What does “reveal” mean on an undermount sink?
Reveal is the visible strip of countertop edge around the sink opening. An overhang reveal covers the sink edge; a positive reveal shows a thin line of the sink. The template gets adjusted for whichever reveal type you choose before cutting.
References & Sources
- Home Depot. “How to Measure a Kitchen Sink” Supports measuring the countertop opening rather than the sink rim on undermount sinks.
- Ruvati. “28-Inch Undermount Kitchen Sink, 16 Gauge Stainless” Source of the verified 28-inch specs: cutout, drain, and minimum cabinet size.
- Foster. “Undermount Sink Installation Instructions (US)” Supports the plywood template method, reveal adjustment, and sink placement from the front edge.
