Carpet Calculator
Calculate carpet area and total cost with 10% waste allowance for any room.
By Syed Mubashir Ali · Last updated
Measuring rooms that are not rectangles
Split L-shaped and irregular rooms into rectangles and add them up, but then sanity-check against roll widths. A room that is 4.2 metres wide on a 4-metre roll either needs a 5-metre roll (with nearly a metre of waste across the whole length) or a seam. Your supplier does this layout daily: take your measurements in and ask.
For stairs, measure one tread (the flat part) plus one riser (the vertical), multiply by the number of steps, and add the width. Then add 10 to 15% because stair carpet cannot be pieced from small offcuts the way a flat floor sometimes can.
What flooring actually costs
The carpet price per square metre is only part of it. Underlay, gripper rods, door thresholds and fitting typically add 40 to 60% on top of the carpet itself. A £20 per square metre carpet in a 20 square metre room is £400 for carpet and roughly £600 to £650 fitted with decent underlay.
Laminate and vinyl plank look cheaper per pack but need the same underlay and often more fitting time for trims and thresholds. Get the all-in fitted price for each option before deciding: the per-square-metre figure on the shelf ticket is never the final number.
How to Use Carpet Calculator
- 1Pick your unit: metres or feet and inches.
- 2Enter the room length and width.
- 3Optionally enter a price per square metre to get a cost alongside the area.
- 4Press Calculate.
- 5You get the net floor area, a gross figure with wastage allowed, and the estimated cost if you supplied a price.
- 6Measure at the widest points. Rooms are rarely perfect rectangles: measure the longest length and the widest width, including alcoves and door recesses. It is better to trim off excess than to discover a shortfall at the far wall.
- 7Note doorways and thresholds. Carpet runs under doors, so include the doorway depth in your length. If two rooms share one run of carpet, measure them as a single area rather than two separate ones.
Frequently Asked Questions
Why is the gross area larger than the net?
Because you cannot lay a floor with zero offcuts. The gross figure allows for trimming and fitting, which is what you actually need to buy: ordering the net area guarantees you come up short.
Does it account for carpet roll widths?
No, and for carpet in particular this matters. Rolls come in fixed widths, commonly 4m and 5m, and a room 4.2m wide may require a 5m roll with substantial waste or a seam. Ask your supplier how your room maps onto their roll widths before ordering.
What about pattern repeat?
Patterned carpet and vinyl need extra for matching across seams, sometimes considerably more. This calculator does not model repeats, so add the allowance your supplier specifies.
Can I use it for laminate or vinyl?
Yes for the area calculation. For plank flooring, buy by pack and round up to whole packs, and keep a spare pack, since batch colours vary and a later repair from a different batch is visible.
How do I handle an L-shaped room?
Split it into rectangles, calculate each, and add them together. Then check the result against roll widths, because an awkward shape often drives more waste than the arithmetic suggests.
How much extra do I need for stairs?
Stairs eat carpet. Allow roughly 10 to 15% extra over the tread-and-riser arithmetic, because each step needs a full width of carpet and the offcuts between steps are mostly waste. A typical straight flight of 13 steps needs about 5 to 6 square metres before wastage.
Broadloom or carpet tiles?
Broadloom (roll carpet) is cheaper per square metre and has no visible joins in a domestic room, but waste is higher on awkward shapes. Carpet tiles waste less, are easy to replace one at a time, and suit offices, but the grid of seams looks commercial, which not everyone wants at home.
Should I include underlay in the cost?
Yes, and do not skimp on it. Good underlay (8 to 11mm, high density) extends carpet life by years and changes how it feels underfoot more than the carpet grade does. Budget roughly half the carpet cost again for underlay and fitting.
About Carpet Calculator
The Carpet and Flooring Calculator works out the floor area of a room in metric or imperial units, adds a wastage allowance, and gives you a cost if you enter a price per square metre. Everything happens in your browser.
The gross figure is the one to order against. Net area is the floor; gross is what you have to buy once trimming and fitting are accounted for, and the gap between them is the difference between a finished room and a second trip to the supplier.
The limitation worth knowing is roll width. Carpet and sheet vinyl come in fixed widths, so a room whose dimensions sit just over a roll width can need far more material than its area suggests, or a seam. Area tells you how much floor there is; your supplier tells you how the roll maps onto it.
For patterned material add the repeat allowance the supplier specifies, and for plank flooring buy whole packs with a spare kept back: batch colour variation makes a later patch from a different pack visible.
The figure that matters is the gross (what you buy) not the net. Flooring is one of the few purchases where the waste is not optional: rolls have fixed widths, rooms have awkward corners, and patterns need matching. A calculator that only gave you the net area would be setting you up for a second trip to the supplier.