Carpet calculator

The same pure function powers the free browser tool and the paid API, so a quote you generate on a phone matches the line item a script posts later. Zero or negative room edges and roll width are rejected with a clear invalid_input message instead of a silent divide-by-zero.

How the carpet linear-metre and area formula works

Start from how carpet is sold in practice: shops cut a fixed-width roll by linear metre, not by freeform polygons. Two strip layouts cover that rectangle. The calculator keeps the cheaper of those two raw linear totals so a four-metre roll in a four-by-five room does not force an unnecessary second strip when one strip already spans the shorter edge. Room area, waste area, and area with waste are reported in parallel so you can audit the plan against a floor-area quote. Waste percent must be non-negative so a zero-waste perfect fit remains expressible without inventing negative material. Your room is a rectangle of room_length by room_width, and the product is a roll of roll_width. In the first orientation, strips run along the room length: you need ceil of room_width divided by roll_width strips, each of length room_length, so linear_along_length equals that strip count times room_length. In the second orientation, strips run along the room width: ceil of room_length divided by roll_width strips each of length room_width gives linear_along_width. After the orientation is chosen, waste_factor equals one plus waste_percent divided by one hundred, linear_meters equals linear_raw times waste_factor, and area_needed equals linear_meters times roll_width—the sheet area you pay for when that length is cut from the roll. The pipeline is deterministic floating-point arithmetic with no random seeds, no wall-clock timestamps, and no network calls, so identical inputs always produce identical JSON. Room length, room width, and roll width must all be strictly positive: zero or negative dimensions are rejected with invalid_input because a zero edge would make coverage undefined and a negative edge is non-physical.

What you send and what you get back

All four fields are required. Classic checks include a five-by-four metre room with a four-metre roll and ten percent waste: one strip along the length yields five raw metres, five point five linear metres after waste, and twenty-two square metres of carpet area. Send four finite numbers: room_length and room_width for the rectangular floor plan in matching linear units, roll_width for the carpet roll width as printed on the product (for example four for a four-metre roll), and waste_percent as the extra material percentage (for example ten for a ten percent allowance). Missing fields, non-numeric strings, NaN, and Infinity fail with invalid_input and are not charged. When any room edge or the roll width is zero or negative the request fails with a message that dimensions must be positive, so clients can correct measurements before retrying instead of receiving Infinity metres. On success the response echoes cleaned inputs, room_area, waste_factor, waste_area, area_with_waste, both orientation candidates (strip counts and raw linear runs), the chosen orientation label, strips, linear_raw, linear_meters after waste, area_needed, spare_area_vs_room (how much purchased sheet area exceeds the bare room), a unit_note reminder to keep one unit system, and a short formula string for documentation. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.

Where carpet calculators show up in real work

Homeowners refreshing bedrooms, living rooms, and hallways need a trustworthy linear-metre figure before a showroom visit or online order, especially when broadloom has a high unit price and dye-lot continuity matters. If you later need floor tile box counts, underlay roll lengths, stair runners with tread and riser breakdowns, or L-shaped room polygons, treat those as separate search intents and landings rather than overloading this carpet linear-metre calculator page. Flooring contractors build room schedules from measured edges and manufacturer roll widths; a single deterministic endpoint that picks the cheaper strip orientation and applies waste reduces spreadsheet drift between the estimator and the purchasing clerk. Interior designers comparing three roll SKUs for the same plan can swap only roll_width and waste_percent while holding room edges fixed, then rank linear_meters and area_needed without re-deriving strip counts each time. Property managers planning multi-unit refreshes feed a batch of room sizes through the API and attach linear_meters to purchase orders so overstock stays intentional rather than accidental. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.