Measuring Irregular Spaces For Carpet Installation

When you’re measuring a room for new carpet installation to try to find out how much material to buy, the process is usually straightforward. Everyone knows that you multiply the length of the room by the width and the number you’re left with is the amount of carpet that you need to buy in square metres. Right?

Measuring And Fitting Carpet
Measuring And Fitting Carpet

Not necessarily. While that calculation works wonders for rooms that are square or rectangular, what happens when you’re working with irregular spaces? So long as you keep a few key calculations in mind, you’ll find the process is just as painless as you had hoped.

Trapezoidal Rooms

If you want to find out how much carpet you’ll need for a room that is shaped like a trapezoid, start by measuring both of the room’s parallel sides in metres. Next, find the height of the room, or the distance between the top side and the bottom side.

Next, take the height and divide it by two. Add the length of the parallel sides together and multiply your two numbers together. The answer that you arrive at is the amount of carpeting you need to buy.

If you had a room with base dimensions of 10 metres and 15 metres and a height of 20 metres, for example, you would start by dividing 20 by 2. Then, add 10 and 15. Multiply the two remaining numbers to arrive at the 250 square metres of carpeting it would take to cover that particular room.


Measuring rooms that are shaped like a parallelogram (or a square that is slightly slanted) is thankfully straightforward. Take the base of the floor plan and multiply it by the height to arrive at the answer. A room with a base of 10 metres and a height of 15 metres breaks down to 10 by 15, or 150 square metres.

Triangular Rooms

If you’re dealing with a room shaped like a triangle (as you might in a situation with something like an attic), you will find the area by first finding the base length and multiplying it by the height, the same way you would in a situation with a parallelogram. Once you have that, multiply it by 1/2 to arrive at the amount of carpet you need to buy. To continue the example of the room above, you would multiply 150 square metres by 1/2 to arrive at 75 square metres of carpeting to install.

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At Fowles, we are proud to be your premiere source for all of your carpet installation and other home improvement needs. Our carpet showroom stocks over 5000 rolls of the latest quality carpet designs at prices up to 40% less than other retailers. Our weekly carpet auctions offer top branded carpet at up to 90% off retail price, and with a free measure and quote service alongside a network of professional carpet fitters, it couldn’t be easier!