Carpet Calculator: Room Size & Roll Length
Compare measured rectangular floor area with full-roll carpet cut length and purchase area, using your chosen direction, roll width, explicit extras or confirmed fitter cut list.
How the estimate works
For each complete rectangle, measured floor area = lengthM × widthM, excluding fitting extras. In your selected direction, unrounded cut length = measured run axis + its explicitly supplied total extra; across-roll need = other measured axis + its total extra. Blank extras add nothing and give only a minimum-before-extra bound. Across-roll need must not exceed rollWidthM. Only plain/nonmatching carpet and, for multiple rooms, explicitly separate unjoined rooms qualify. A supplied positive roundingStepM rounds each cut upward separately using safe final whole-increment counts; no step means no rounding. Total cut length is the sum of qualified cuts only when the whole active list is complete; full-roll purchase area = rollWidthM × totalCutLengthM. Confirmed fitter cuts replace rectangle arithmetic, without extra allowances. No area ÷ roll width order calculation, strip splitting, orientation choice or intermediate rounding.
Pure supplied-fact arithmetic for one selected carpet/roll width and only the entered list. Blank fitting extras are minimum-before-extra, not guaranteed order-ready. Nonrectangular rooms, stairs, matching patterns, needed or uncertain joins, incomplete rows and unknown roll width cannot produce a complete rectangle-derived order. No seam/cutting optimisation, offcut reuse, product suitability, pile-direction, fitting, price, stock, seller-order or Materials List guarantee. No automatic quantities for underlay, grippers or doorbars.
Worked example
Hypothetical supplied-fact example, not a product quote or fitting recommendation: a complete rectangle has length 4 m and width 3 m, so measured floor area is 12 m². You choose a 4 m roll and a cut running along the length. Your fitter supplies total length extra 0.2 m and total width extra 0.1 m: the cut is 4.2 m long, needs 3.1 m across, and fits by width arithmetic. If your seller separately specifies a 0.5 m each-cut step, that cut rounds up to 4.5 linear metres; full-roll purchase area is 4 × 4.5 = 18 m², not 12 m². The 6 m² difference is not promised reusable offcut. Plain/nonmatching carpet is explicitly confirmed; no defaults, seam plan, stock or sufficient-order guarantee are implied.
What to measure and check
Measure the room’s complete dimensions, including relevant doorways, bays and alcoves. Confirm that those dimensions describe an actual complete rectangle, not a bounding box for an irregular floor. Choose the roll width from your exact carpet listing and choose the cut direction yourself. Confirm no pattern/stripe matching and, for multiple rooms, separate unjoined rooms. Enter only seller/fitter-supplied total fitting extra along each axis; extras are not per-edge and are never doubled. For complex or joined layouts, use complete fitter-supplied cuts instead. Numeric inputs start blank.
How should I measure a room?
Record actual longest/widest dimensions including doorways, bays and alcoves. Rectangle mode requires those dimensions to describe the complete rectangular floor. Do not call an irregular bounding box actual floor area; use professional measuring/planning and the fitter-cut shortcut for irregular layouts.
Why is full-roll purchase area larger than floor area?
A cut uses the entire selected roll width, even if the room is narrower. Explicit fitting extras and any supplied each-cut rounding step can add more. Measured rectangular floor area excludes extras; purchase area is roll width times total cut length. The difference is not guaranteed waste or reusable offcut.
Is a standard fitting or waste allowance included?
No. Source guidance differs: Online Carpets describes adding a DIY extra, while Tapi records actual dimensions and adds allowances later. Supply fitter/seller-confirmed total extra along each axis; it is not doubled or applied per edge. Blank extras give clearly labelled minimum-before-extra quantities, not an order-ready guarantee. Explicit zero is accepted only as your supplied fact.
What if my room is wider than the roll?
The chosen across-roll dimension plus its total extra must fit the selected roll. The calculator never swaps orientation, divides area by roll width, or splits the room into strips. It may flag that the opposite direction fits by width arithmetic, but you must explicitly choose it after checking pile/direction needs. If neither fits, obtain a fitter cut list for joins.
Can it plan patterned carpet, joins or stairs?
No. Pattern/stripe matching, stairs, nonrectangular floors, connected rooms and uncertain joins need a fitter cutting plan. Rectangle-derived totals require explicit no-matching confirmation and, for multiple rooms, separate unjoined rooms. There is no seam optimisation, offcut reuse, pile-direction or fitting guarantee.
Can I enter measurements in other units?
Use the interface length-unit choices where available; stored fields and this calculation remain canonical metres. Commercial outputs are clearly labelled linear m and m². Changing display units must not change the measured quantity or round it prematurely; these lengths are not roll counts.
How does the fitter-cut shortcut work?
Choose cut-list mode, select the exact roll width, enter every complete fitter-supplied cut length and explicitly confirm the list came from your fitter. No second fitting or pattern allowance is added. Only a seller rounding step you supply rounds each cut upward. Floor area cannot be inferred from that list; keep different carpets or roll widths separate.
What happens with blank rows, missing facts or seller rounding?
Wholly unused blank rows are ignored, but a named or partially started row prevents a complete total until resolved. Available individual facts remain visible. Missing roll width, directions or required confirmations do not produce a whole-list order. A blank rounding step leaves cuts unchanged; a positive supplied step rounds each qualified cut separately before summing. Always check the seller’s final rules and fitter’s completed plan.
Where the numbers come from
Formula version v1.0. Implemented and tested 11 November 2026. Product-dependent figures remain your supplied facts; a cited example is not a selected product or a universal yield.
- Online Carpets — quick room measurement guide (fixed roll widths and measuring guidance; no universal allowance adopted) — checked 2026-11-11
- Tapi — how to measure a room (actual measurements before later allowances) — checked 2026-11-11
- Tapi — measuring and planning (professional help for complex rooms and stairs) — checked 2026-11-11