Carpeting over hardwood costs $2.50 to $8 per sq ft fully installed, the same as carpet over any plywood subfloor. The cost question is the easy part. The harder question is whether you should be doing this at all, given the tack-strip damage to refinishable hardwood beneath, the $3,000 to $10,000 resale-value impact, and the area-rug alternative that almost always serves the same goal at lower cost and zero permanent damage.
Carpet over hardwood is one of the few flooring decisions where the honest answer is usually no, and the right alternative is an area rug. There are three cases where wall-to-wall carpet over hardwood genuinely makes sense, and most homeowners asking the question are not in any of them.
The first legitimate case is basement-converted living space with old softwood floors. Pine and fir floors from pre-1950 homes that have been sanded and refinished multiple times eventually reach a state where the remaining wood thickness will not support another refinishing pass. In that case the hardwood has no future and carpeting over it is fine. The second case is HOA-mandated carpet in townhouses or condos above another unit, where the building's sound-isolation requirements (typically IIC 50+ rated underlayment) effectively require wall-to-wall carpet rather than rugs. The third case is long-term hold (15+ years) with pets or young children, where the practical reality is that the hardwood is going to take damage anyway and a sacrificial carpet layer protects it for the years that the household most needs the comfort of carpet.
Outside these three cases, the right answer is usually an area rug. A 9×12 or 10×14 rug covers the central conversation area of most living rooms, provides the underfoot comfort that drove the question, costs less than wall-to-wall, is removable for cleaning or refinishing the floor, and does not damage the hardwood beneath. The wood remains visible at the room perimeter, preserving the architectural feature and the resale value.
Tack strips are the wood-or-plastic strips with sharp upward- facing pins that hold wall-to-wall carpet in tension around the perimeter of the room. They are nailed to the subfloor every 6 to 8 inches around the entire room perimeter. On a standard 12×15 living room, the perimeter is 54 linear feet, which means roughly 100 to 200 nail penetrations into whatever subfloor is below. When the subfloor is plywood, the holes do not matter; the plywood is hidden forever. When the subfloor is finished hardwood, every nail penetration is permanent damage to a visible surface.
The nail holes themselves are small, about 1/16 of an inch across, and individually inconspicuous. The problem is that they appear in a regular pattern around the perimeter of the room, which the human eye reads as a clear line under raked light or low-angle sunlight. Filling the holes with wood putty during a later refinishing job partially masks them but rarely completely. The honest expectation is that any room that has been carpeted with wall-to-wall over hardwood for even one cycle will show a perceptible perimeter pattern in the wood after carpet removal.
Hardwood floors are a positive feature in nearly every US residential real estate market. Appraisers note them, listing agents photograph them, and buyers will reliably pay more for a home with exposed hardwood than the same home with the hardwood covered. Industry remodelling reports from the National Association of Realtors consistently put the hardwood-exposed premium at $3,000 to $10,000 on a typical single-family home, and higher in metros where hardwood is considered a baseline feature (Northeast, Pacific Northwest, Chicago). The financial impact of carpeting over hardwood extends beyond the install cost itself; if you are within 5 to 10 years of selling, the carpet install is effectively subtracting future resale value at roughly twice its installation cost.
The install itself is straightforward. The hardwood floor functions as a stable, flat subfloor for the carpet install. Tack strips are nailed around the perimeter (with the unavoidable damage discussed above), 8 lb rebond pad is rolled out, and the carpet is cut, stretched, and trimmed. The labour is identical to a carpet-over-plywood install at $0.50 to $1.50 per sqft labour. The pad is identical at $0.30 to $0.50 per sqft. The carpet is whatever fibre you select. Total all-in is $2.50 to $8 per sqft for standard nylon, the same as the base case. If your room is also above another unit and requires acoustic pad upgrade, add $0.45 to $0.90 per sqft for that.