Carpet Calculator

Carpet Ordering Guide

How Carpet Is Sold

Carpet is unusual among home materials in how it's sold — it comes off a single roll as one continuous piece cut to length, and you pay for the rectangular area of the cut piece even if your room shape doesn't use all of it. Standard UK carpet roll widths are 4 m, 5 m, and (less commonly) 3 m, 3.66 m, and 2.74 m. You order the roll width multiplied by the length of strip you need to cover the room — so the amount you pay for is always a rectangle, not your actual room shape. For a room 5.5 m × 3 m using a 4 m wide roll: you can't get the 5.5 m length out of a 4 m wide strip without joining, so the calculation goes one of two ways. Option 1: order a 5.5 m length of 4 m wide carpet (22 m²), then have a seam to extend the width from 4 m to 5.5 m using a remnant — wasteful. Option 2: order a 5 m wide roll if available (5.5 × 5 = 27.5 m²) so the carpet covers full width with offcuts at the end — less waste but more expensive roll. Option 3: orient the carpet with pile running across the room rather than along, using less length but potentially compromising the look. For irregular L-shaped rooms or rooms with bays, the rectangle that contains the room (the bounding box) is what you order, with significant offcut waste. A worked example: a 4.2 m × 3.5 m room with a 1.5 m × 0.5 m alcove takes 4.2 × 3.5 = 14.7 m² of bounding rectangle, plus the alcove's 0.75 m² if it sits outside that rectangle, plus 5–10% for trimming, fitting, and pattern matching. Calculating carpet from your actual area underestimates; calculating from the roll-width × room-length bounding box is correct. This calculator gives the practical figure including roll width considerations and waste.

Seams and Direction

Carpet seams and pile direction matter more than people expect, and getting them right separates a good fitting job from one that looks visually wrong even when the carpet itself is fine. The standard rule: run the carpet pile in the direction of natural light, towards the main window of the room. The pile lay catches light differently from different angles — looking with the pile makes the carpet appear darker and richer; looking against the pile makes it appear lighter and sometimes patchy. Running pile towards the main light source gives the most flattering view from the entrance of the room and minimises visible variation in tone across the floor. For seams (unavoidable in rooms wider than the roll), the principle is to put them where they're least seen — away from the main sight lines and out of high-traffic areas. Seam placement options: along a wall (least visible but lots of trimming); under a piece of fixed furniture if any exists; running parallel to and offset from the main doorway sight line. Modern seaming with hot-melt seam tape is invisible when done well, but always shows as a faint line if positioned in the wrong light. For pattern-matching carpets (any with a discernible pattern beyond plain cut-pile texture), allow an extra 5–10% in length so the fitter can offset and align patterns across seams — this is essential, and most pattern-matched carpets fail when fitted by inexperienced installers who don't allow enough material to align the pattern. Stripes and herringbone patterns need particular care to run in the right direction relative to the room shape. A professional fitter calculates pile direction and seam placement before cutting; for DIY, plan it before ordering. This calculator gives you the basic quantity; the layout planning belongs at the survey stage.

Underlay First

Underlay is often treated as an afterthought to carpet, but it deserves more attention because it dramatically affects how the finished floor feels, sounds, and how long the carpet lasts. Quality underlay (10–11 mm thick PU foam, or quality rubber crumb) extends carpet life by an estimated 50% — the underlay absorbs the wear stress that would otherwise compress the carpet fibres and break them down over time. The same carpet on cheap thin underlay versus quality 10 mm PU underlay can last 7 years versus 12+ for the same family use. Underlay also adds significant warmth (improves the floor's R-value, reducing heat loss through the floor) and acoustic insulation (sound absorption underfoot, which transforms how a wood-floor-style apartment feels). For underlay quantity: use the same m² calculation as the carpet itself (it goes underneath, after all), but typically a slightly smaller waste allowance (5% instead of 10%) since underlay rolls are wider than carpet rolls and need less complex cutting. Don't reuse old underlay when fitting new carpet — modern carpets are designed for modern underlays, and 10–15-year-old underlay has often degraded to brittle foam that performs much worse than new. Specific situations: for underfloor heating, specify low-tog underlay (under 1.0 tog, ideally 0.7 or less) — high-tog underlay insulates against the heating and defeats the system; cork or specialist UFH-compatible underlay is the right choice. For stairs and high-traffic landings, use heavier-grade underlay rated for these areas. Avoid the cheapest underlay: spending 15–25% of the carpet cost on underlay versus 5% gives a noticeably better floor for decades. This calculator includes underlay area; specify quality and tog separately.

Energy Efficiency Priorities

Home energy improvements should be prioritised by payback period. Quickest payback: draught proofing (£50-200 cost, saves £60-100/year — under 2 years). Loft insulation (£300-500 DIY, saves £150-200/year — 2-3 years). Switching to LED lighting (under £100, saves £40-60/year — under 2 years). Longer payback: cavity wall insulation (3-5 years). New efficient boiler (5-10 years). Solar panels (7-15 years). Heat pump (10-25 years at current energy prices). For homes eligible for ECO4 funding, the pa