Carpet Calculator — How Much Carpet Do You Need?
Carpet is sold by the linear metre from a roll of fixed width, so you need more than just the room area to order correctly. This calculator works out the square metres needed (with waste) and converts that into the linear metres you quote to the carpet supplier.
How we calculate
Floor area = length × width. Area with waste = floor area × (1 + waste %). Linear metres = ⌈area with waste ÷ roll width⌉ (rounded to 1 decimal).
Worked example
A 4 m × 3 m room (12 m²) with 10% waste needs 13.2 m². From a 4 m wide roll: 13.2 ÷ 4 = 3.3 linear metres.
Common mistakes
- Quoting the room area to the supplier instead of the linear metres — you will get cut short.
- Forgetting that a patterned carpet needs extra for matching repeat patterns (add 15–20%).
- Not checking the roll width — a 3 m wide roll in a 4 m wide room always creates a seam.
- Ignoring the direction of the pile — running the pile the wrong way can make seams more visible.
Frequently asked questions
How do I order carpet from a supplier?+
Suppliers sell carpet by the linear metre from a fixed-width roll (usually 4 m or 5 m wide). Tell them the linear metres you need, not the room area. Use this calculator to convert your room dimensions into the correct linear metre figure.
How much extra carpet should I allow for waste?+
Allow 10% for a plain carpet in a simple rectangular room. Increase to 15–20% for patterned carpets that need pattern matching at joins, and for L-shaped or irregularly shaped rooms with more offcuts.
What roll width should I choose?+
Choose a roll width wider than your room to avoid seams if possible. A 4 m wide roll covers rooms up to 4 m in one direction without a join. For wider rooms, a 5 m roll or carefully planned seam positions are needed.
Does carpet need underlay?+
Yes. Underlay extends the life of carpet, improves comfort underfoot, and provides thermal and acoustic insulation. It is sold separately and is not included in carpet calculations. Use the Underlayment Calculator for roll quantities.