Carpet Calculator
Estimate carpet area and cost for a room, with a waste allowance for cuts and seams.
How to use this calculator
- 1Measure the area. For an irregular space, split it into rectangles, work each out, and add them.
- 2Set the unit you measured in — the calculator converts everything for you.
- 3Check the coverage figure against the bag or tin you are actually buying; it varies between brands.
- 4Leave the waste allowance on. Running short mid-job costs far more than one spare unit.
How the calculation works
Units = ⌈ (Area × (1 + waste)) / Coverage per unit ⌉- Area
- Surface area of the job
- waste
- Allowance for cuts, breakage and spillage
- ⌈ ⌉
- Round up — you cannot buy a fraction of a unit
Every dimension is converted to metres internally, so feet, yards and metres can be mixed with inches or centimetres without error.
Carpet is sold from a roll of fixed width — commonly 3.66 m (12 ft) or 4 m broadloom. If the room is wider than the roll a seam is unavoidable, and waste rises sharply because the offcut strip is often too narrow to use elsewhere.
Set coverage to 1 to work in square metres. For carpet tiles set it to the area of one tile and the result becomes a tile count.
Worked example
A 20 × 12 ft area
- 1.20 ft × 12 ft = 240 sq ft, which is 22.30 m².
- 2.Divided by the coverage per square metre, that gives the raw requirement.
- 3.A 10% waste allowance is added, then the figure is rounded up to whole square metres.
Result: See the result panel — it updates live as you change the numbers.
What this assumes, and where it stops
Assumptions
- The area is flat and regular as described. Slopes, steps and obstructions change the quantity.
- Coverage figures are the manufacturer’s stated values, which assume good conditions and an even surface.
- The area entered is the finished floor area to be covered.
Limitations
- This estimates material only — not labour, tools, delivery, hire or disposal.
- Manufacturer coverage varies between brands and batches. Always check the packaging.
- Does not account for roll width. A room wider than the available broadloom needs seam planning, which can add more waste than a flat percentage captures.
- Underlay, gripper rod, door bars and fitting are not included.
- Patterned carpet needs matching across seams, which adds waste the same way wallpaper does.
Common questions
How much extra carpet should I order?
Around 10% for a simple rectangular room. Add more for L-shaped rooms, several doorways, or if the room is wider than the carpet roll and needs a seam. Stairs are a separate calculation and need considerably more than their floor area suggests.
Do I need underlay as well?
For broadloom carpet, almost always — it extends carpet life substantially and adds comfort and insulation. Underlay is bought to the same floor area, though without the pattern-matching allowance. Carpet tiles usually have integral backing and need none.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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