Broadloom carpet comes off rolls 12 ft (3.66 m), 13 ft 2 in (4 m) or 15 ft (4.57 m) wide, so you pay for whole strips even when the room is narrower. Lay the strips along the longest wall where possible to minimise seams, and allow about 3 in at each end for trimming. Padding and installation are priced on the actual floor area.
How to use the Carpet Calculator
- Room shape
- Room length (or diameter)
- Room width
- Roll width
- Trim allowance per end
- Carpet price
- Padding price
- Installation price
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the room shape and enter its size, the roll width and trim allowance, and prices for carpet, padding and installation. The calculator decides how many strips are needed, how much carpet that is and the total cost.
Tips for an accurate estimate
- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer’s coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.
Common mistakes to avoid
- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.
Inputs explained
| Field | What to enter |
|---|---|
| Room shape | Choose one: Rectangle, Circle |
| Room length (or diameter) | Units: ft, m, in, yd, cm |
| Room width | Units: ft, m, in, yd, cm |
| Roll width | Choose one: 12 ft, 13 ft 2 in (4 m), 15 ft, 5 m |
| Trim allowance per end | Units: in, cm, mm, ft, m |
| Carpet price | Units: /yd², /ft², /m² |
| Padding price | Units: /yd², /ft², /m² |
| Installation price | Units: /yd², /ft², /m² |
What each result means
- Carpet to buy = [Strips (seams = strips − 1)]×([Room length (or diameter)] + 2×[Trim allowance per end])×[Roll width]
- Waste = ([Carpet to buy] – [Floor area])÷[Carpet to buy]×100
- Total cost = [Carpet to buy]×[Carpet price] + [Floor area]×([Padding price] + [Installation price])
Example values
How the main result changes when Room length changes and everything else stays at the example values above:
| Room length (or diameter) (ft) | Carpet to buy (ft²) |
|---|---|
| 7.5 | 96 |
| 11.25 | 141 |
| 15 | 186 |
| 18.75 | 231 |
| 22.5 | 276 |
| 30 | 366 |
Formula
Strips = ceil(room width ÷ roll width)Carpet to buy = strips × (room length + 2 × trim) × roll widthCost = carpet × price + floor area × (pad + installation)Worked example
Inputs — Room shape: Rectangle; Room length (or diameter): 15 ft; Room width: 12 ft; Roll width: 12 ft; Trim allowance per end: 3 in; Carpet price: $30 /yd²; Padding price: $5 /yd²; Installation price: $7 /yd².
Results — Floor area = 180 ft²; Strips (seams = strips − 1) = 1; Carpet to buy = 186 ft²; Waste = 3.2 %; Total cost = $860.00.
Frequently asked questions
How much carpet do I need for a 12 × 15 room?
On a 12 ft roll, one strip 15 ft 6 in long: 186 ft² (20.7 yd²).
What width does carpet come in?
Most broadloom is 12 ft wide; some is 13 ft 2 in (4 m) or 15 ft.
How much padding do I need?
Padding is cut to the floor area, so buy the area of the room plus a little waste.
What formula does the Carpet Calculator use?
Strips = ceil(room width ÷ roll width).