3mm to 15mm: How to Pick the Right Sintered Slab Thickness for Your Project

Most sintered slab specifications start with the question "what colour" and end without anyone asking the more important one: "how thick?" The factory gives you a default — usually 12mm — and the project moves on. That default is right about half the time. The other half, you're either over-spending or asking a 6mm slab to do the work of a structural countertop.

Standard sintered slab thicknesses run 3mm, 6mm, 9mm, 12mm, and 15mm. Each one solves a different problem.

3mm — wall cladding only

A 3mm slab weighs about 8kg per square metre. At 1600×3200mm — the largest standard format — a single panel is roughly 38kg. One installer can carry it. Two installers can mount it on a wall.

This is the thickness for vertical surfaces only: feature walls in lobbies, fireplace surrounds, behind-bar panels, refurbished elevator interiors. It is too thin for any horizontal application that takes weight, too thin to fabricate a square edge that won't chip in transport, and too thin to mitre. Order it pre-finished, pre-cut, and bond it to substrate on site.

6mm — versatile cladding, light flooring

Six millimetres is the workhorse cladding thickness. It is the dimension architects specify for rainscreens, ventilated façades, large-format wall panels indoors, shower walls, and interior partitions. It can also be used for residential floors with proper substrate, though anything with rolling load (commercial trolleys, retail) calls for thicker.

The selling point: continuous coverage. A 1600×3200mm wall panel at 6mm reads as a single piece of marble across an entire wall. The grout joint visible behind a sofa in a marble-tiled wall — gone.

9mm — the under-recognised middle

Nine millimetres is the thickness most distributors don't bother to stock and most architects don't think to ask for. It is the right answer for furniture: dining tables, coffee tables, vanity tops in apartments where the slab edge is exposed but the visual weight of a 12mm or 20mm edge would feel chunky.

It is also the ideal thickness for shower trays, where you want enough mass to set drainage falls reliably and enough thinness to keep the shower flush with surrounding floor tile.

12mm — kitchen countertops by default

Twelve millimetres is what every kitchen-countertop salesperson defaults to, and they are mostly right. It carries the load of standing on it during installation, accepts a clean mitre to fabricate a 30mm or 60mm visual edge, and is thick enough that a chip on the corner can sometimes be filled rather than catastrophic.

It is also the standard thickness for hospitality bar tops, reception desks in commercial fit-outs, and any horizontal surface that will see contact from people, glasses, or restaurant trays.

15mm — heavy commercial and exterior

Fifteen millimetres is overkill for most kitchens. It is the right answer for high-traffic commercial floors, exterior paving where freeze-thaw cycles matter, and pool surrounds where structural reliability under repeat thermal stress is non-negotiable.

Outside of those use cases, 15mm is a budget hit without a corresponding upgrade in performance. We see it specified often by architects defaulting to "thicker is better" — and that instinct is wrong half the time.

Visual edge thickness is a separate question

A 30mm visual edge does not require a 30mm slab. It requires a 12mm slab cut twice with a 45° mitre and bonded with a coloured epoxy. A 60mm edge takes three pieces. The technique is called mitred edge fabrication, every competent stone fabricator does it, and it lets you have the chunky aesthetic of a thick slab while keeping material weight, shipping cost, and installation effort proportional to a thinner one.

Specify thickness for structural performance, not for appearance. The mitred edge handles appearance.

What to ask the supplier

Three questions worth asking before placing an order. What thicknesses do you stock locally versus produce on order — affects lead time. What is the maximum slab dimension at this thickness — affects design. What is the rejection rate at this thickness for visible defects — affects how many spares you need to factor in. A serious factory answers all three without hedging.

If you want to see the full thickness range in stock — 3mm through 15mm across the major colour families — the catalog is filtered by thickness directly.