Carpet pad is chosen at the end of a long shopping process, usually from a wall of samples that all feel more or less the same underfoot in the showroom. Two numbers are printed on them: a thickness in fractions of an inch and a density in pounds. Most people assume the bigger number in each case is better. Density and thickness pull in opposite directions more often than they agree, and getting that backwards is what causes carpet to ripple, wrinkle, and wear out years early.
Density Is Not Thickness
Density is the weight of one cubic foot of the pad material, written as 6 lb, 8 lb and so on. It describes how tightly packed the foam is, which is what determines whether the pad springs back after a footstep or gradually stays compressed.
Thickness is simply how tall the pad is, typically between 1/4 and 1/2 inch. It determines how soft the floor feels the moment you step on it.
The two are independent. A thick, low-density pad feels wonderful in the store and is the worst thing you can put under most carpet, because it lets the carpet backing flex too far with every step. That flexing breaks down the latex that holds the tufts in place, and it lets the carpet shift on the tack strip until it ripples. A thinner, denser pad feels firmer in the showroom and keeps the carpet flat for a decade.
The practical rule: density is the durability number and thickness is the comfort number, and durability should win wherever people actually walk.
What Each Density Rating Is For
| Density | Where it belongs | What to expect |
|---|---|---|
| 3–4 lb | Rentals and short-term flips | Landlord grade. Compresses permanently within a couple of years and often falls below carpet warranty minimums. |
| 5 lb | Closets, guest rooms, low-use spaces | Acceptable where nobody walks daily. Not enough for a hallway. |
| 6 lb | Bedrooms | Softer underfoot, adequate for light traffic. The common builder default. |
| 8 lb | Living rooms, family rooms, whole-house | The best general answer. Costs very little more than 6 lb and holds its shape far longer. |
| 10 lb and up | Stairs, hallways, home offices with chairs | Firm underfoot. Necessary where the pad takes concentrated or rolling loads. |
The gap between 6 lb and 8 lb is where most of the decision sits, and it is worth knowing that the price difference is usually a few cents per square foot. On a 200 square foot bedroom that is often under twenty dollars across the life of the carpet. There are few upgrades in a house with that ratio of cost to consequence.
The Warranty Clause Nobody Reads
Carpet manufacturers specify a minimum pad density and a maximum pad thickness for each carpet line, and installing outside that window can void the wear warranty. This matters because the two failure modes it prevents are exactly the ones people cause by choosing on feel.
The minimum density stops you from putting a soft pad under a carpet that needs support. The maximum thickness surprises people more: a pad thicker than the specification allows the carpet to move enough that the seams and the stretch fail, and the manufacturer will not cover the resulting wrinkles. Berber and other low-profile loop carpets have the strictest limits, often 3/8 inch or less at a high density, because their tight construction has almost no give of its own.
Get the specification from the carpet manufacturer rather than the salesperson. It is normally on the product page or the warranty sheet, and it takes one phone call otherwise. If you are having carpet installed, confirm in writing which pad is being used, because pad is a common place for a quote to be quietly downgraded.
Three Rooms That Break the General Rule
- Stairs. Every step concentrates a person's full weight on the nosing, which is the worst load case in the house. Use a high-density pad at reduced thickness, typically 8 to 10 lb at 3/8 inch or less. A thick pad on stairs makes the carpet roll over the nosing edge and wear through there first, and it is also a genuine trip hazard on the tread edge.
- Basements and concrete slabs. Concrete releases moisture upward year-round. A pad with a bonded moisture barrier keeps that from reaching the carpet backing, where it feeds mildew you will smell long before you see it. This matters more than the density number in a basement, and rubber pads outperform foam here.
- Rooms with rolling chairs. A desk chair is a rolling point load, and it will trench a soft pad in the shape of your movement radius. Treat a home office like a hallway: 10 lb or firmer, or a chair mat over a standard pad.
Pad Types, Briefly
| Type | Density range | Notes |
|---|---|---|
| Rebond (bonded urethane) | 5–10 lb | The multicoloured recycled foam that covers most residential jobs. Best value; buy 8 lb. |
| Frothed foam | 12+ lb | Denser and longer-lived than rebond; costs more. |
| Slab rubber | 18–22 lb | Very firm and very durable. Common over concrete and in heavy-use areas. |
| Fiber (felt) | Rated in ounces | Firm and low-profile. A good fit under Berber and looped styles. |
| Memory foam | Varies | Sold on showroom feel. Check it against the carpet's density minimum before buying. |
Rebond is what almost everyone ends up with, and that is fine. The decision inside rebond is the density number, not the brand.
Ordering Pad
Pad is sold by the square foot or square yard in rolls, most commonly 6 feet wide, which is half the width of a standard 12-foot carpet roll. That difference matters when you estimate: your pad seams will not line up with your carpet seams, and they should not, because overlapping seams create a ridge you can feel through the carpet.
Order pad to the same square footage as the carpet including waste, then add a little for the stairs if you are running a different pad there. Pad is easier to cut and piece than carpet, so the waste factor is lower, but running short mid-installation means a second trip for a partial roll. For room-by-room square footage and the carpet waste factor, the carpet calculator gives both.
The Bottom Line
Buy 8 lb rebond for most of the house. Step up to 10 lb or firmer for stairs, hallways and rooms with rolling chairs, and add a moisture barrier over concrete. Keep 6 lb for bedrooms only if the price difference genuinely matters, and treat anything at 4 lb or below as a rental-grade product. Before you finalise, check the carpet's own specification for its minimum density and its maximum thickness, because that document, not the way the sample feels in your hand, is what decides whether the warranty stands.
Frequently Asked Questions
Is 6 lb or 8 lb carpet pad better?
For anywhere with daily foot traffic, 8 lb. The higher density keeps its shape under repeated compression, which keeps the carpet flat and protects the backing from flexing. A 6 lb pad is reasonable in a bedroom or a guest room where it will not be walked on constantly. The price difference between the two is usually a few cents per square foot, which makes 8 lb the default worth buying almost everywhere.
Does thicker carpet padding mean better padding?
No, and past a point it is actively worse. Thickness controls how soft the floor feels; density controls how long the carpet lasts. A thick low-density pad lets the carpet backing flex too far with every step, which breaks down the latex holding the tufts and allows the carpet to shift and ripple. Most carpet warranties specify a maximum pad thickness for exactly this reason.
What carpet pad should I use on stairs?
A high-density pad at reduced thickness, usually 8 to 10 lb at 3/8 inch or less. Stairs concentrate a person's whole weight on the nosing edge, and a thick pad lets the carpet roll over that edge so it wears through there first. A softer, thicker pad on stairs also creates a spongy tread edge that is a real trip hazard.
Can the wrong carpet pad void my carpet warranty?
Yes. Carpet manufacturers publish a minimum pad density and a maximum pad thickness for each carpet line, and installing outside that range can void the wear warranty. Berber and other low-profile loop carpets have the tightest limits, often 3/8 inch or less at a high density. Ask for the specification sheet rather than relying on a salesperson's recommendation, and if you are hiring an installer, confirm in writing which pad they are using.
Do I need a moisture barrier pad in a basement?
Over a concrete slab, yes. Concrete releases moisture upward continuously, and without a barrier that moisture reaches the carpet backing and supports mildew growth, which you will smell before you see it. A pad with a bonded moisture barrier, or a rubber pad, is the standard answer below grade. In a basement this decision matters more than the density rating does.