The most expensive measurement in an outdoor kitchen is the one nobody wrote down. A grill listed as 40 inches wide does not need a 40-inch hole — it needs a 38-inch hole, because the two inches of difference are the flange the grill rests on. Cut it at 40 and the grill drops straight through.
This page is the reference we send to homeowners and fabricators before anyone touches stone. It covers how a drop-in grill actually seats, what each of the three cutout dimensions means, a model-by-model table for KoKoMo built-in appliances, and the mistakes that turn a finished island into a rebuild.
How a drop-in grill actually sits
A built-in grill head has a flange running around the full perimeter — on KoKoMo units, roughly one inch on all four sides. The grill lowers into the opening and the flange lands on the countertop lip, carrying the weight and concealing the rough cut edge underneath.
That geometry produces three rules that govern everything else:
- The opening is always smaller than the grill. If the cutout equals the grill’s outside width, there is nothing for the flange to sit on.
- The countertop carries the load, not the cabinet interior. On a 40-inch head that is well over a hundred pounds resting on a two-inch lip of stone. The material and its support matter.
- The cutout dimensions come from the manufacturer, never from measuring the grill. Measuring the grill body gives you the outside dimension, which is exactly the wrong number.
What the three numbers mean
Width is the horizontal opening across the face of the island. Height is the vertical drop of the opening below the countertop — the space the firebox occupies inside the cabinet. Depth is front to back. Height is the one people forget to check, and it is the one that stops a grill from seating flush.
KoKoMo built-in cutout dimensions
Cutout figures below are the manufacturer’s published opening dimensions. Overall dimensions are the physical unit, listed so you can sanity-check clearance inside the cabinet and plan the lift.
KO-BAK3BG23½″8⅝″21¼″25″ × 18½″ × 24⅜″
KO-PRO-4BG30⅞″8⅝″21¼″32½″ × 18½″ × 24⅜″
KO-BAK5BG38″8⅝″21¼″39¾″ × 18½″ × 24⅜″
KO-PRO-5BG38″8⅝″21¼″39¾″ × 18½″ × 24⅜″
KO-CHAR3231″12″18½″32½″ × 24½″ × 24″
KO-GRDL30-PRONot published——28½″ × 9″ × 19¼″
Three things worth noticing in that table. First, the four gas grills share an identical cutout height and depth — 8⅝ inches by 21¼ inches — so only the width changes across the line. Second, the Classic and Professional 40-inch models take the same opening, which means you can change your mind between those two lines late without touching the island. Third, the charcoal unit is a genuinely different shape: deeper vertically, shallower front to back. Do not assume it drops into a gas cutout.
The perimeter flange is what conceals the cut edge — which is why the opening has to be undersized relative to the grill.
The dimensions that are not on the cutout sheet
A correct opening in the wrong structure is still a failed install. Four requirements sit alongside the cutout numbers.
Non-combustible construction
The island must be built from non-combustible material throughout. Framing a grill cutout in wood is the most common and most serious error in do-it-yourself outdoor kitchen builds, and it is not made safe by lining the opening.
Clearance to combustibles
KoKoMo specifies a minimum of 14 inches from the sides and 16 inches from the back to adjacent combustible construction. The use-and-care section of the Professional manual also directs users to keep the appliance at least 18 inches from combustible material — follow the more restrictive figure that applies to your installation.
Gas access and shutoff
Route the line away from heat sources and sharp edges with as few bends as possible, and confirm the connection point and shutoff stay accessible once the grill is seated and the panels are on. Connection work belongs with a licensed gas professional.
Electrical, if the model needs it
Professional Series models with interior lighting, hood lights, or illuminated knobs require an outdoor-rated grounded supply. Getting power into the plan before anything is poured costs almost nothing; retrofitting it into finished masonry is an expensive afternoon.
The sequence that avoids rework
Pick the appliance first
The grill is an input to the island design, not a decision you make after it. Every dimension downstream depends on which head you chose.
Get the current cutout sheet in writing
Not a retailer listing, not a forum post, not this page. The manufacturer document for your exact model and revision. Print it.
Design the island around the opening and the clearances
Width of the run, depth of the cabinet, position of the grill within the run, and where the counter space lands on each side.
Rough in gas and power before the shell closes
Both are trivially easy at this stage and painful at any later one.
Take delivery and verify against the physical unit
Measure the grill you actually received against the sheet. This is the step that catches revision changes, and it takes five minutes.
Then cut
Stone is unforgiving. A cutout can always be made larger; it can never be made smaller.
Seven cutout mistakes we see repeatedly
1. Cutting to the grill’s overall width
The single most common failure. A 39¾-inch grill needs a 38-inch opening. Cut it at 39¾ and there is no flange bearing surface at all.
2. Ignoring the cutout height
Width gets checked. Height gets assumed. If the vertical opening is short, the grill sits proud of the counter and nothing about the install looks right.
3. Using an older revision of the spec sheet
Manufacturers revise these. Cutout figures on one KoKoMo sheet carry a revision code precisely so installers can confirm they are working from current data.
4. Building the island first and shopping later
This inverts the whole process. You end up choosing from whatever grill happens to fit the hole you already made, which is a much smaller list than the one you started with.
5. Forgetting the clearance to combustibles
Fourteen inches from the sides and sixteen from the back is a design constraint on the island, not an installation detail. It changes cabinet depth.
6. No access to the gas shutoff after the build
Every appliance eventually needs service. If the shutoff ends up sealed behind finished stone, that service call becomes a demolition call.
7. Planning a one-person install
A 40-inch head runs around 138 pounds crated and the manual specifically calls for two people to seat it. Freight delivery is typically curbside or driveway, and placement into the island is not included.
Cutout questions we answer on the phone
What happens if the cutout is slightly too big?
It depends how slightly. The flange gives you about an inch of coverage per side, so a small overcut may still be concealed — but you lose bearing surface, and bearing surface is what holds a hundred-plus pounds of grill. If you have overcut, stop and have your fabricator assess whether the lip is still adequate before seating anything.
What if it is too small?
Better problem. Stone can be taken away. Have the fabricator enlarge it to spec rather than forcing the grill, which can distort the flange and leave the unit sitting unevenly.
Can I replace an old built-in with a new one using the existing hole?
Sometimes, and it is worth checking before you assume otherwise. Measure the existing opening — width, height, and depth — and compare it against the cutout figures for the models you are considering. Both KoKoMo 40-inch grills take a 38-inch opening, so if that is what your island has, you have options. Send us the measurements and we will tell you what fits.
Do built-in grills need an insulated jacket?
It depends on the appliance and the enclosure. Requirements come from the specific model’s current installation instructions, so confirm the enclosure material, ventilation openings, combustible clearances, and any jacket requirement against those documents rather than a general rule.
Does the countertop material change the cutout?
Not the dimensions, but it changes how the cut is made and how the edge is finished. Granite, concrete, porcelain, and tile all behave differently under a saw. This is your fabricator’s domain — give them the manufacturer sheet and let them determine method.
Can I get the cutout sheet before I order?
Yes. We send the current spec sheet and installation guide for the exact model you are considering, including confirmed cutout dimensions and electrical requirements, before you build. Ask at 833-777-2962 or info@smokeforges.com.
Send us the numbers before your fabricator commits
Ten minutes confirming a cutout costs nothing. A freight return on a 138-pound crate, or a recut on finished stone, costs considerably more. We will check your opening against the exact unit shipping to you, confirm gas configuration and clearances, and flag anything that looks off in the plan.
Prefer email? Reach us at info@smokeforges.com
Related reading: How to Plan an Outdoor Kitchen and Built-In vs. Freestanding Grill. Browse the KoKoMo built-in collection.
