Carpet Calculator

Carpet is one of the few things you buy where you also pay for the parts that get thrown away. It comes off a roll in a fixed width, the pile has to run the same direction across the whole room, and everything the fitter trims off at the skirting board is still on the invoice. This calculator turns two room measurements into the numbers that decide your order: the floor area, the quantity to buy once waste is allowed for, and what that costs at the rate you have been quoted.

What the calculator works out

Four inputs drive every result — length, width, a waste factor and a price per unit area. The maths is deliberately simple, so you can check it by hand:

• Total area is length × width. The default 12 ft × 10 ft room gives 120 sq ft.
• Waste is that area multiplied by your waste percentage — 10% of 120 sq ft is 12 sq ft.
• Carpet needed is area plus waste, so 132 sq ft.
• Estimated cost is the carpet needed × your price. At $3.50 per sq ft that is $462.00, not $420 — you are billed on the full quantity ordered, waste included, exactly as a real quote works.

The unit tabs switch the whole tool over. Feet mode starts at 12 × 10 at $3.50 per sq ft; metres mode at 4 × 3.5 at $25 per m². Switching resets those fields to samples rather than converting your entries, so treat each tab as a fresh start. To move a figure between systems, use the area converter.

Measuring the room so the number is right

• Measure at the widest point, wall to wall. Take the length in two or three places and use the largest. Walls bow, and carpet cut to the narrow measurement cannot be stretched to fit the wide end.
• Include alcoves and the doorway. Bay windows, chimney recesses and the floor inside a doorway all need covering. Carpet usually stops under the closed door, so measure to the centre of the opening.
• Enter decimals. Each field takes one number, so 12 ft 6 in is 12.5 — a half foot is 6 in, a quarter is 3 in. In metric, 3 m 40 cm is 3.4.
• Split awkward shapes into rectangles that do not overlap at the corner, then run the calculator once for each.
• Deduct nothing for furniture. Carpet is fitted under and around it, and you pay for the full floor.

Choosing a sensible waste factor

The waste field starts at 10% and accepts up to 50%. As a general rule of thumb in the flooring trade, around 10% suits a plain carpet in a simple rectangular room, and you go up when the job is harder to cut efficiently:

• Patterned carpet has to be matched across seams, which means cutting extra length at every join. Large repeats waste the most.
• Roll width matters more than people expect. Carpet is sold in fixed widths, so a room wider than the roll gets a seam plus a full-length offcut. A percentage is a cushion, not a cutting plan.
• Stairs and hallways generate heavy waste, because every tread and turn is a separate piece.
• Angled walls leave triangular offcuts that cannot be reused elsewhere.

What the estimate leaves out

This is a materials figure for the carpet alone. Underlay, gripper rods, door bars, removal of the old floor, fitting labour, delivery and sales tax are all extra, and on a small room they can rival the carpet itself. The tool also assumes your price is per square foot or per square metre; some suppliers still quote per square yard, which is nine square feet, so divide such a price by 9 first. Redecorating at the same time? The paint calculator handles wall area and coverage on the same principle.

How to use the Carpet Calculator

1. Choose Feet / Inches or Meters / cm at the top — this sets every label and result unit.
2. Enter the room length and width as decimals, measured at the widest points.
3. Set the waste factor: 10% for a plain carpet in a plain room, higher for patterns, stairs or awkward shapes.
4. Enter the price per sq ft (or per sq m) as quoted, converting from square yards first if needed.
5. Read the four cards — total area, carpet needed, estimated cost and waste. Everything updates as you type.
6. For an L-shaped room, note the first rectangle's result, enter the second, and add the two carpet-needed figures.

Frequently Asked Questions

How much extra carpet should I order?

The 10% default is a common starting point for a rectangular room with a plain carpet. Push it to 15–20% for patterned carpet, several alcoves, or a job including stairs. If your fitter has quoted a quantity, use theirs — they can see the roll width and seam positions.

Does the estimated cost include underlay and fitting?

No. It multiplies the carpet quantity by the price you enter, nothing more.

My room is L-shaped. Can the tool handle it?

Not in one pass, since it multiplies a single length by a single width. Split the floor into rectangles, calculate each, and add the carpet-needed figures. That also over-allows slightly for waste, which is the safer direction.

Can I type feet and inches, like 12' 6"?

No — enter 12.5. Divide the inches by 12 to get the decimal part.

My supplier quotes per square yard. What do I enter?

Divide by 9, because a square yard is 3 ft × 3 ft. A $27 per square yard carpet is $3.00 per square foot.

Does it account for roll width and seams?

No, and that is its main limitation. It calculates area and adds a percentage; it does not plan how your room is cut from a roll of a given width, which is what decides real waste on wide or oddly proportioned rooms. Use the result as a budget estimate and let a fitter produce the cutting plan.