Carpet Padding Calculator

Installing carpet requires purchasing both the carpet itself and the pad underneath. The pad (also called underlay) provides cushioning, insulation, and extends the life of the carpet. This calculator estimates both quantities, including a standard waste allowance for cuts and seams.

The formula:

Room Area = Length × Width

Order Area = Room Area × (1 + Waste Factor)

A typical waste factor is 10% for simple rectangular rooms. For rooms with multiple angles, alcoves, or closets, use 15–20%.

Standard carpet roll widths, and why the area figure is not what you pay for

Carpet comes off a roll, almost always 12 feet (3.66 m) wide in North America, occasionally 15 feet. You cannot buy 198 square feet of it. You buy a length of full-width roll, and the offcut is yours whether you want it or not.

That changes the number badly once a room is wider than the roll:

• A 12 × 15 ft room fits inside one roll width. You buy 15 running feet of 12 ft carpet: 180 sq ft, no seam, and almost nothing wasted.
• A 13 × 15 ft room does not. Whichever way you turn it, a second strip is needed. Running the strips the short way is the cheaper of the two, at 2 × 13 ft: 312 sq ft bought to cover 195 sq ft of floor, and one seam down the middle.

One extra foot of room width adds 132 sq ft to the order. That is why installers ask for the width before anything else, and why a 15-foot roll is worth asking about even at a higher price per yard.

The calculator tries both orientations and quotes the cheaper one. Ask your installer which way they intend to run it, because the seam should follow the light from the main window rather than cross it.

The calculator below reports both figures: the area with waste, which is what a pad priced by the square foot costs, and the roll-based purchase, which is what the carpet actually costs.

Carpet padding types and thicknesses:

Typical carpet costs (United States):

• Budget carpet: $1–3 per ft² ($10–32 per m²)
• Mid-range carpet: $3–5 per ft² ($32–54 per m²)
• High-end carpet: $5–10+ per ft² ($54–108+ per m²)
• Carpet padding: $0.50–2.00 per ft² ($5–22 per m²)
• Installation: $1–2 per ft² ($10–22 per m²)

Metric note:

• 1 square yard = 0.836 m²
• 1 square foot = 0.0929 m²
• Carpet is often sold by the square yard in older US pricing

Tips for buying carpet:

• Always measure twice before ordering.
• Buy from the same dye lot for color consistency.
• Thicker pads feel more luxurious but are not always better. Check the manufacturer’s recommendation for your carpet type; many warranties are void over a certain pad thickness.
• Berber and loop carpets require a thinner, firmer pad to avoid stretching.
• Ask your installer about the seam placement before cutting begins.