Carpet Calculator

1. Measure the room. Record the longest length and widest width in feet and inches. Measure at the widest points, including doorway recesses and closet openings. Older rooms often have walls that are not perfectly square, so measure both ends and use the larger number.
2. Enter feet and inches. Type the feet in the first field and extra inches in the second. For a room that measures 15 ft 6 in, enter 15 in feet and 6 in inches. This carpet calculator converts automatically to give you carpet square footage.
3. Set room quantity. If you have multiple identical rooms (such as three matching bedrooms), enter the count instead of measuring each one separately.
4. Choose a waste factor. Use 10% for simple rectangular rooms. Increase to 15% for stairs, patterned carpet, L-shaped rooms, or rooms with multiple seams. Angled walls and hallways with turns also waste more material.
5. Add stairs (optional). Enter the number of steps, stair width, tread depth, and riser height. Standard residential stairs are about 3 ft wide with 10 in treads and 7 in risers. The stair carpet calculator section handles the extra area automatically.
6. Enter price (optional). Add the carpet price per square foot if you want a carpet cost estimate. This covers carpet material only, not padding, installation labor, tack strips, or removal of old flooring.

Pro tip: Measure into doorways and include closets before adding waste. Carpet installers cut from a single roll when possible, so the roll width (12 ft or 15 ft) matters more than raw carpet square footage. A room that is 13 ft wide needs a 15 ft roll with 2 ft of waste on each row.

Common mistake: Measuring only the visible floor and forgetting closets, hallway recesses, and the area under door swings. These missed spots add up quickly. A single missed closet can mean a second trip to the store or a costly short-roll order.

This carpet calculator estimates how much carpet to buy in four steps: calculate the area, add stairs, apply waste, and convert units. Use it as a carpet square foot calculator, carpet yardage calculator, or carpet cost calculator depending on your inputs.

Room area:

Room area (sq ft) = Length (ft) × Width (ft) × Number of rooms

Convert any inches to decimal feet first. For example, 15 ft 6 in becomes 15.5 ft (6 / 12 = 0.5).

Stair area (optional):

Stair area (sq ft) = Stair width (ft) × (Tread depth + Riser height) / 12 × Number of steps

Each step needs carpet across the tread (horizontal surface) and the riser (vertical face). A 3 ft wide stair with a 10 in tread and 7 in riser covers 1.42 sq ft per step.

Waste:

Adjusted area = Total area × (1 + Waste % / 100)

Waste covers cuts at walls, seam overlaps, pattern matching, and irregular edges. A 10% waste factor on 200 sq ft adds 20 sq ft.

Conversion:

Square yards = Adjusted area (sq ft) / 9

Roll length (linear ft) = Adjusted area / Roll width (ft)

Variables:

• Length = longest wall measurement in feet and inches
• Width = widest wall measurement in feet and inches
• Number of rooms = count of identical rooms sharing the same dimensions
• Waste % = extra material for cuts, seams, and fitting (default 10%)
• Roll width = carpet roll width, typically 12 ft or 15 ft
• Tread = horizontal depth of one stair step in inches
• Riser = vertical height of one stair step in inches

Example:

A bedroom measures 12 ft × 15 ft. A closet adds 4 ft × 6 ft. You choose 10% waste.

• Bedroom area = 12 × 15 = 180 sq ft
• Closet area = 4 × 6 = 24 sq ft
• Total area = 180 + 24 = 204 sq ft
• Waste = 204 × 0.10 = 20.4 sq ft
• Adjusted area = 204 + 20.4 = 224.4 sq ft
• Square yards = 224.4 / 9 = 24.93 sq yd
• Roll length (12 ft roll) = 224.4 / 12 = 18.7 linear ft
• At $3.50 per sq ft, the carpet estimate comes to $785.40 for material

Assumptions and limitations:

• This carpet calculator estimates material quantity for rectangular rooms. L-shaped or irregular rooms should be split into rectangles and measured separately.
• Carpet rolls come in fixed widths (usually 12 ft or 15 ft). If your room is wider than the roll, the installer adds seams. Seam placement affects the actual amount of carpet needed, so your final purchase quantity may differ from this carpet estimate.
• Stair calculations assume standard straight-run stairs. Winder stairs, pie-shaped steps, and landings require separate carpet measurement.
• The carpet price estimate covers material only. It does not include padding, tack strips, seam tape, installation labor, or old carpet removal. Budget $1 to $3 per square foot for padding and $3 to $6 per square foot for professional installation (2026 prices).
• Round up your purchase quantity. Carpet remnants from the same dye lot are hard to find later if you need repairs.