Carpet Calculator
By Taro Schenker | Updated February 11, 2026
Quick Answer: To calculate carpet, multiply Length (ft) x Width (ft) to get square feet, then divide by 9 to convert to square yards. Carpet rolls are 12 or 15 ft wide; divide room width by roll width and round up for the number of strips. Seams = strips minus 1. Carpet weighs approximately 2.5 lbs per sq yd (~40 oz/sq yd). Padding area equals carpet area. Add 10% for waste. For a 12 x 15 ft room, you need 20 sq yd (about 22 sq yd with waste), one strip from a 15 ft roll, zero seams.
Calculate how much carpet you need for any room, multiple rooms, or stairway. Enter your dimensions to get the exact amount in square yards, linear feet of roll, number of seams, padding area, and estimated cost.
How to Calculate Carpet
The formula for calculating carpet area is straightforward:
- Measure the length and width of your room in feet.
- Multiply length × width to get the area in square feet.
- Divide by 9 to convert to square yards (carpet is sold per square yard).
- Determine how many strips you need based on roll width (12 or 15 ft).
- Add 10% for waste, seams, and pattern matching.
Carpet Sizing Guide
Quick reference for common room sizes and carpet needed:
| Room Size | Square Feet | Square Yards |
|---|---|---|
| 10 × 10 | 100 sq ft | 11.1 sq yd |
| 12 × 12 | 144 sq ft | 16.0 sq yd |
| 12 × 15 | 180 sq ft | 20.0 sq yd |
| 15 × 15 | 225 sq ft | 25.0 sq yd |
| 15 × 20 | 300 sq ft | 33.3 sq yd |
| 20 × 20 | 400 sq ft | 44.4 sq yd |
Understanding Carpet Rolls
- Roll widths: Carpet comes in standard widths of 12 feet and 15 feet. Choosing a roll width that matches or exceeds your room width minimizes seams and waste.
- Seams: When your room is wider than the roll, you need additional strips and seams. Each seam adds a potential wear point, so plan seam placement in low-traffic areas. A 14-foot wide room on a 12-foot roll requires 2 strips and 1 seam.
- Waste: Carpet is sold in rectangular pieces cut from the roll. Irregularly shaped rooms, closets, and doorways increase waste. Budget 10% extra for standard rooms and 15-20% for complex layouts or patterned carpet that requires matching.
- Direction: All carpet pieces in a room should run in the same direction (the pile direction). This affects how you cut strips from the roll and can influence total linear feet needed.
Formula Summary
Carpet Area Formula: To calculate carpet needed, compute the floor area in square feet, convert to square yards, then apply the waste factor.
$$A_{\text{sq yd}} = \frac{L_{\text{ft}} \times W_{\text{ft}}}{9}$$
$$A_{\text{adjusted}} = A_{\text{sq yd}} \times (1 + W_f)$$
Strips and Seams: $$\text{Strips} = \lceil \frac{W_{\text{room}}}{W_{\text{roll}}} \rceil \quad,\quad \text{Seams} = \text{Strips} - 1$$
Linear Feet: $$LF = \text{Strips} \times L_{\text{room}}$$
Weight Formula: $$W_{\text{lbs}} = A_{\text{adjusted}} \times 2.5$$ (carpet density ~40 oz/sq yd = 2.5 lbs/sq yd)
| Constant | Value |
|---|---|
| Sq ft per sq yd | 9 |
| Carpet weight | 2.5 lbs/sq yd (~40 oz/sq yd) |
| Standard roll widths | 12 ft or 15 ft |
| Default waste factor | 10% |
Standard Assumptions: Waste factor of 10% accounts for seams, pattern matching, and cutting. Padding area equals adjusted carpet area. For stairways, each stair area = stair width (in) / 12 x stair depth (in) / 12. Cost = adjusted sq yd x 9 x price per sq ft.
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Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.