5mm, 6.5mm or 8mm? SPC Flooring Thickness, Explained

Almost every customer who calls us asks the same question within the first two minutes: how thick should my floor be? It is a fair question and a badly answered one. Most of what is written about it online confuses total thickness with wear layer, and treats "thicker" as a straight synonym for "better." It isn't.

Here is what the number actually means and what it changes.

What the millimeter number measures

The millimeter figure is the total thickness of the plank — the rigid stone-polymer core, the printed decor film, the clear wear layer on top, and on most products an attached underlayment pad on the bottom. It is not the wear layer. The wear layer is measured separately in mils, and that is the number that governs how long your floor resists scratching and scuffing. We cover it properly in our guide to wear layer.

So what does total thickness do? Three things, in order of how much you will notice them:

1. It hides subfloor imperfections. A thicker, stiffer core bridges small dips and high spots instead of telegraphing them through to the surface. This is the biggest practical difference.
2. It changes how the floor sounds and feels. Thicker planks with a good attached pad feel more solid underfoot and sound less hollow.
3. It affects height at doorways. An 8mm floor plus pad is close to half an inch. Interior doors and appliance clearances sometimes need attention.

What thickness does not do is make the floor more waterproof or more scratch resistant. Those come from the core material and the wear layer respectively.

The subfloor is what decides this

If you take one thing from this page, take this: choose thickness based on your subfloor, not your budget.

Rigid core plank is a floating floor. It does not stick down, so it can only ever be as flat as what it sits on. Every manufacturer specifies a flatness tolerance — commonly in the region of 3/16" over 10 feet — and ignoring it is the single most common cause of a floor that clicks, flexes or separates at the seams a year later.

• A clean, flat concrete slab — new construction, a well-poured basement — is the easiest case. A 5mm plank is genuinely fine here.
• Plywood over joists in an older home is usually the hardest case. Older houses around central New Jersey frequently have some deflection between joists and a few decades of settling. Go thicker.
• Over existing tile, the grout lines must be filled and the surface leveled first, whatever thickness you choose. A thicker plank is more forgiving but it is not a substitute for prep.

How our four series compare

We carry four series. They differ in exactly two ways that matter — core thickness and wear layer — plus plank format.

Picking in practice

Choose Alpine (5mm) when the subfloor is flat and sound and you are covering a lot of ground. It is our most affordable series and it carries the same 22 mil wear layer as Montclair and Harper, so you are not giving up surface durability — only core stiffness. It is the right call for a rental turnover or a bedroom level over a decent slab.

Choose Montclair or Harper (6.5mm) for most houses. This is the thickness that handles a normal, slightly imperfect subfloor without complaint, feels solid underfoot and still sits at a sensible height against existing thresholds. Montclair and Harper are built the same way — the difference is the plank. Harper is a 9" wide, 48" long board, which reads calmer and more contemporary in an open room because you see fewer seams.

Choose Citadel (8mm) when the subfloor is the problem, the household is hard on floors, or the space sees something closer to commercial traffic. It is also the only one of our four with a 32 mil wear layer, which is above what most residential products carry and into the range usually specified for commercial work.

A note on "thicker is quieter"

Thickness helps, but it is not the whole story, and if you live in a condo or co-op it is almost certainly not the number your building wants. Buildings that regulate floor noise specify an IIC or STC rating for the finished assembly — plank plus underlayment plus structure — not a plank thickness. If your building has a sound requirement in writing, send it to us before you order and we will tell you honestly whether we can meet it.

Still not sure?

Order samples of the two series you are deciding between. Put them on the actual floor, in the actual room, and walk on them. Five minutes of that settles the question better than any article, including this one.