How the length is worked out
The area is the room length multiplied by the room width. That is the figure you compare with the price per square metre.
The length off the roll is different. If the room is wider than the roll, the carpet is laid in strips, so the length ordered is the room length multiplied by the number of strips.
A 5 m by 4 m room on a 4 m roll needs one 5 m length. The same room on a 3 m roll needs two strips, which is 10 m of carpet for 20 square metres of floor.
Worked example
A room 5 m by 4 m is 20 square metres, or 23.92 square yards. On a 4 m roll that is a 5 m length, and with 5 per cent waste it is 5.25 m.
The square yard figure matters because some carpet is still priced that way, and a square yard is 0.836 square metres.
Waste, direction and pattern
Five per cent covers trimming and a simple layout. A patterned carpet needs more, because each strip has to be matched, and the match can waste most of a strip.
Pile direction matters. Two strips cut from different parts of a roll can look different shades if the pile runs the other way, so order all the carpet at once.
Underlay and gripper are separate. Underlay is sold by the square metre and is usually worth more than the difference between a cheap and a good carpet.
Limits of this calculator
It assumes a rectangular room. An L-shaped room, a bay or a room with a chimney breast needs each rectangle measured, and the total length is not simply the sum of the areas.
It does not account for the roll width available for your chosen carpet, which may be narrower than the standard.
It does not include fitting, underlay, gripper, door bars or the cost.
For a hard floor instead, use the tile calculator.
Inputs for the carpet calculator
Room length
Length of the room in metres, measured wall to wall.
Room width
Width of the room in metres, measured at the widest point.
Carpet roll width
Width the carpet is woven in, usually 4 m or 5 m.
Waste allowance
Extra for trimming and pattern matching. Five per cent suits a plain carpet.
CALCULATOR QUESTIONS
Carpet calculator questions
How much carpet for a 5 by 4 metre room?
20 square metres, which is a 5 m length off a 4 m roll, or 5.25 m with waste.
Why order by length, not area?
Carpet comes off a roll of fixed width, so you pay for the full width whether you use it or not.
How many square yards is a square metre?
One square metre is 1.196 square yards, so 20 square metres is 23.92 square yards.
Does this include underlay?
No. Underlay, gripper and fitting are separate.