Carpet Calculator
Estimate carpet for a room, accounting for the fixed roll width that broadloom carpet comes in — which drives more waste than tile-based flooring. Get the linear length, total area and cost.
How to use this calculator
- Enter the room length and width.
- Choose the carpet roll width — 4 m is most common.
- The calculator picks the orientation with least waste and adds trimming allowance.
Formula used
Because broadloom comes in a fixed width, a room narrower than the roll still buys the full width — the leftover strip is waste. The calculator compares both orientations and picks whichever wastes less carpet.
Example calculation
A 5 m × 4 m room (20 m²) with a 4 m roll: the 4 m side fits the roll exactly, so buy 5 m of length. With 10% trim → 5.5 m × 4 m = 22 m² purchased for a 20 m² room.
If the room were 4.5 m wide, you'd need two widths or a seam — jumping the purchase well above 20 m².
Why carpet wastes differently
Unlike tiles or planks that come in small units, broadloom carpet is one continuous piece off a fixed-width roll (commonly 4 or 5 m). That changes the waste maths entirely: a room narrower than the roll still pays for the full roll width, and a room wider than the roll needs a seam and a second width, which can nearly double the purchase.
Orientation therefore matters a lot — running the carpet the "right" way can be the difference between one clean width and an expensive seam. Seams also want to run away from doorways and main sightlines where they'd show and wear. The calculator picks the lower-waste orientation, but for tricky rooms a professional fitter's plan can save more than the fitting costs.
Why use this calculator?
- Accounts for fixed roll width — the thing that makes carpet waste unusual.
- Compares both orientations to minimise cost.
- Shows how much you're paying over the bare room area.
Frequently asked questions
How is carpet measured and sold?
By the linear metre off a fixed-width roll (usually 4 or 5 m wide). So you buy "5 metres of 4 m carpet" = 20 m², regardless of your room's exact shape — narrower rooms still pay for the full roll width.
How much extra carpet should I allow?
About 10% for trimming and fitting, more for stairs, irregular rooms or where seams and pattern matching are involved. Getting the room measured professionally before ordering avoids costly mistakes on big rooms.
Why might a small room need more carpet than its area?
The fixed roll width. A 3 m wide room cut from a 4 m roll wastes a 1 m strip along its length — you pay for carpet you don't use. Choosing the roll width and orientation carefully minimises this.