Formula
Measured area = room length × room width. Planning area = measured area × (1 + waste percent ÷ 100). Approximate roll length = planning area ÷ roll width. Optional material cost = planning area × price per square metre.
Carpet Calculator
Estimate carpet area, waste allowance, roll length and optional material cost from room measurements and carpet roll width.
Worked example
For a 4.8 m × 3.6 m room, measured area is 4.8 × 3.6 = 17.28 m². A 10% allowance gives 17.28 × 1.10 = 19.008 m², shown as 19.01 m². With a 3.66 m roll width, approximate roll length is 19.008 ÷ 3.66 = 5.19 m.
Professional note
Master’s Tip: print the measured area and the allowance separately before ordering. A supplier or installer may choose a different seam layout, especially for patterned carpet, stairs, bay windows or rooms wider than the roll.
Regional and unit assumptions
Standard or basis: transparent rectangular area arithmetic in metres. Carpet roll width, waste percentage, seam layout, pattern repeat and supplier rounding are practical job assumptions that must be checked against the selected product.
Assumptions and limitations
- The room is treated as a simple rectangle; alcoves, closets, stairs and irregular edges need separate measurement or added allowance.
- Waste allowance is a planning input, not a guarantee. Pattern matching, pile direction, seams and installer layout can change the order quantity.
- Roll length is approximate and should be rounded using the supplier’s ordering increments and carpet width.
- The optional cost is material-only arithmetic. It excludes underlay, gripper, trims, delivery, labour, removal, stairs and tax unless you include them separately.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Measured area = room length × room width. Planning area = measured area × (1 + waste percent ÷ 100). Approximate roll length = planning area ÷ roll width. Optional material cost = planning area × price per square metre.
Standard or basis
Standard or basis: transparent rectangular area arithmetic in metres. Carpet roll width, waste percentage, seam layout, pattern repeat and supplier rounding are practical job assumptions that must be checked against the selected product.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: print the measured area and the allowance separately before ordering. A supplier or installer may choose a different seam layout, especially for patterned carpet, stairs, bay windows or rooms wider than the roll.
Related calculators
Questions
How do I calculate how much carpet I need?
Multiply room length by room width to get measured square metres, then add a waste or trimming allowance. Divide the planning area by roll width if you need an approximate linear roll length.
How much extra carpet should I allow?
A simple room may use a modest allowance such as 5–10%, while patterned carpet, joins, stairs, closets or awkward shapes can require more. The calculator lets you change the allowance visibly.
Does roll width affect carpet quantity?
Yes. The square-metre area is the same, but the linear metres from the roll depend on roll width and seam layout. Supplier rounding can also change the final order.
Can this calculator price a carpet job?
It can estimate material cost if you enter a price per square metre. It does not include labour, underlay, trims, delivery, removal, stair work, tax or installer-specific charges.
Is this enough for patterned carpet?
Use it as an early planning worksheet only. Pattern repeat, pile direction and seam placement should be checked by the supplier or installer before ordering.
Calculation note
Carpet estimating is a practical area calculation with a real-world ordering layer. The arithmetic is simple, but the buying decision depends on roll width, seams, trimming, pattern repeat and the installer’s layout plan.
Measured floor area is only the starting point
A rectangular room can be measured with length multiplied by width, but carpet is not poured into the room like liquid. It arrives in rolls, is cut, seamed and trimmed, and may need extra material for direction or pattern alignment.
Allowances should be visible, not hidden
A waste percentage is a planning assumption. Showing it separately helps homeowners, tenants, landlords and tradespeople discuss whether the allowance fits the room shape, closets, stairs, doorways and chosen carpet.
Printable records help quotes stay comparable
A printed carpet worksheet can be attached to supplier quotes or site notes. Keeping measurements, roll width, formula, allowance and notes together makes it easier to compare offers without losing the original measurement basis.