Carpet Calculator
How much carpet do you need? Measure any number of rooms, add a waste factor, and get the square footage, quantity and cost to order.
A worked example
A 12 × 15 ft room is 180 square feet. Adding the 10% waste factor this calculator defaults to brings that up to 198 square feet to buy — 17 roll feet, at 12 sq ft each. At the mid-range price of $6.00 per square foot that is about $1,188.00.
| Grade | Price per sq ft | 180 sq ft room, installed |
|---|---|---|
| Budget | $3.00 | $594.00 |
| Mid-range | $6.00 | $1,188.00 |
| Premium | $12.00 | $2,376.00 |
Price ranges are broad US ballpark figures for material plus typical installation, gathered as placeholders and not yet verified against sourced pricing. Use them to sanity-check a quote, not to replace one. Broadloom carpet comes on 12 ft wide rolls, so one lineal foot of roll covers 12 sq ft.
To compare quotes on the same basis, see how to calculate price per square foot.
Roll width changes everything
Carpet is the one floor covering where the area alone does not tell you what to order. It comes off a roll of fixed width — usually 12 feet, sometimes 15 — and that width has to span one direction of the room in a single piece. A 13 foot wide room cut from a 12 foot roll needs a seam and a second strip, and the leftover from that strip is waste you still pay for.
Work in square feet for the estimate, then let the fitter confirm the cutting plan. On a room that only just exceeds the roll width, a 15 foot roll can work out cheaper overall despite the higher price per square foot.
Square feet or square yards
Carpet is quoted both ways, and the two differ by a factor of nine — one square yard is exactly nine square feet. A price that looks three times higher than another is very often the same price expressed per square yard, so check the unit before comparing quotes. The calculator shows the area in both.
Waste, alcoves and stairs
Ten percent is a reasonable allowance for a simple rectangular room. Allow more when the room is wider than the roll, because the offcut from the second cut is rarely usable elsewhere. Measure a doorway alcove or a bay window into the main rectangle rather than adding it separately — the carpet has to be cut from one piece, so its extent is what matters, not its area.
Stairs are quoted by the tread rather than by area, and are usually priced separately. Underlay covers the same floor area but comes in different roll sizes and has no pattern to match, so 5% waste is normally enough where the carpet needs 10 — expect the two orders to round up differently.
Frequently asked questions
How do I calculate how much carpet I need?
Measure the floor area in square feet as usual, then remember that carpet is sold from a roll of fixed width — usually 12 ft, sometimes 15 ft. The roll width has to span one direction of the room, so a 13 ft wide room cut from a 12 ft roll needs a seam and a second strip, and the offcut is waste you still pay for. Work in square feet for the estimate and let the fitter confirm the cutting plan.
Is carpet sold by the square foot or the square yard?
Both, depending on the supplier, and the difference is a factor of nine — one square yard is exactly 9 square feet. A price that looks three times higher is usually the same price quoted per square yard, so check which unit a quote uses before comparing two of them. This calculator shows the area in both.
How much extra carpet should I allow?
Ten percent on a simple rectangular room, and more when the room is wider than the roll, because the leftover strip from the second cut is rarely usable elsewhere. Stairs are quoted separately by the tread rather than by area, and a room with a doorway alcove or a bay window needs the alcove measured into the main rectangle, since the carpet has to be cut from one piece.
Do I need to measure for underlay separately?
Underlay uses the same floor area, but it is sold in its own roll widths and lengths, so the two orders round up differently — you can easily need 10 square feet more of one than the other. Underlay has no pattern to match, so 5% waste is usually enough where the carpet needs 10%.