Carpet Calculator

How the carpet calculator works

The calculator gives the room's floor area:

Area (m²) = length (m) × width (m)

Carpet is different from other flooring, though, because it comes off a roll of fixed width. You buy lineal metres off the roll, so the amount you pay for is often more than the floor area.

Roll widths

In Australia, carpet is commonly made in 3.66 m (12 ft) widths, with some ranges at 4 m. The aim is a layout with as few joins as possible, with any joins placed out of the main traffic and light.

Worked example: a 4.2 m × 3.5 m bedroom

1. Floor area: 4.2 × 3.5 = 14.7 m²
2. The room is 3.5 m wide, which fits within a 3.66 m roll, so there's no join
3. Carpet to buy: room length plus about 100 mm of trim each end = 4.4 lineal metres
4. 4.4 × 3.66 = 16.1 m² of carpet bought for 14.7 m² of floor

A 4.5 m wide room would need either a 4 m roll plus a strip, or a join across a 3.66 m roll. That's why the room's shape matters more than its area when pricing carpet.

Also allow for

• Underlay: the floor area plus about 5%
• Stairs: each step needs roughly 0.9 m × the stair width, depending on tread and riser size. Carpet layers usually price stairs per step.
• Smooth edge (gripper) and trims: measure the room perimeter and doorways

Common mistakes

• Pricing by floor area when you're paying for roll width × length.
• Letting joins run across doorways or in front of windows, where they show most.
• Not allowing for pile direction. All pieces must run the same way or the shade will look different.

How much carpet do I need for a room?

Measure the room, then work out lineal metres off a 3.66 m or 4 m roll. Add 100 mm at each end for trimming.

How do I calculate carpet for stairs?

Allow about 0.9 m of carpet per step (tread plus riser plus wrap) for a standard stair, then confirm with your carpet layer.

What is the standard width of carpet?

3.66 m (12 ft) is most common in Australia, with some ranges at 4 m.

Written by Sam Alex, civil engineer. About the author