Carpet Calculator
Estimate the carpet area and cost for a room, including waste and padding.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
For a rectangular room, this estimate compares the roll length in both room orientations, then adds your waste allowance. It uses roll width to estimate carpet purchased; seams, doorways, pattern matching and stair cuts need a supplier’s measured plan.
Worked example
calculated with the default values below
Room length 15 ft · Room width 12 ft · Waste allowance 10 % · Carpet roll width 12 ft · Price per square yard 22 $ · Padding per square yard 5 $ Room area 180.0 sq ft · Carpet area with waste 22.00 sq yd · Carpet cost 484.00 $ · Padding cost 110.00 $ · Total cost 594.00 $
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
Total = L × W × (1 + w ÷ 100) ÷ 9 × (p + p_pad)
- L
- Room length (ft)
- W
- Room width (ft)
- w
- Waste allowance (%)
- p
- Carpet price per sq yd
- p_pad
- Padding price per sq yd
- Total
- Total carpet cost
Room area = length × width. Estimate the shorter carpet roll run in either room orientation; purchased carpet area = roll width × roll run × (1 + waste%). Carpet and padding costs use the estimated purchase area. Layout details such as stairs, doorways and pattern matching are not modeled.
Frequently asked questions
How does roll width change the carpet estimate?
The estimate calculates room floor area, compares the roll length needed with the room in both orientations, then applies the waste percentage. At 15 × 12 ft with a 12-ft roll and 10% waste, the estimated carpet order is 22 sq yd. Padding and carpet costs use that estimated purchase area. The layout does not model doorways, stairs, pattern matching or installer-specific seams, so confirm measurements with a flooring professional.