If you haven’t already done so, it is highly recommended that you read about how to measure for carpet before reading this article, to have a firm grasp of the basics of measuring before you move on to the more difficult calculations.
Once you have figured out your room dimensions, you are ready to start determining how to lay on your carpet. The first thing to note is the direction of the carpet pile.
Direction of the Pile
The most important rule in carpet is that you must always keep the carpet running in the same direction. You can't turn one piece sideways to the other. Doing so will cause the two pieces to look very different from each other, sometimes even like different colors.
In order to keep the carpet running in the same direction, you may need to buy more carpet than you actually need. Consider this: a hallway 3' wide by 12' long runs into a room that is 12' by 9', so that the room and the hall together form a T shape (see the above image, where the lines represent the pile direction).
With a carpet that comes in a 12' width, the shortest measurements would dictate that you buy a piece of carpet 12' by 9' for the room, and another 12' by 3' for the hall. However, this would mean that the 12' by 3' piece of carpet for the hall was turned sideways to fit. This is represented in the above image by the lines, which indicate the direction of the carpet.
Keep the Pile Direction Consistent
There are two ways to handle the situation described on the previous slide, with one way being optimal for carpet performance.
Option 1: The best way to install this would be to purchase a 12' by 9' piece of carpet for the room and another 12' by 12' for the hall. It's a lot of extra carpets that you don't need. But doing it this way not only maintains the direction of the carpet but gives a better performance of the carpet in the hallway. Carpet should run in the direction of the traffic. Repeated traffic against the grain, or pile direction, leads to premature wear of the carpet. This option is represented in the image above.
Option 2: The second option would be to purchase a 12' by 12' for the room, and a 12' by 3' for the hall. This would result in less waste (i.e., carpet that doesn't get used) as it would leave you with only 3' by 12' of leftover carpet, instead of 9' by 12' in the first option.
Even though it costs more and leaves more carpet unused, Option 1 is the best option because the carpet will stand up better in the hallway. However, Option 2 could be considered for lower traffic households, or for a more budget-friendly installation. Additionally, if you are carpeting stairs which lead off the hallway, Option 2 may be necessary (depending on the layout) to keep a patterned carpet lined up as it goes over the edge of the stairs.
Installing the carpet in either of these two ways avoids having seams in the high-traffic area of the hall. And hopefully, you will be able to find a use for the extra material -- maybe you'll also be carpeting your stairs, and can use the off-cuts to cover them. Or, perhaps turn the leftover carpet into a runner or area rug.
Rooms Wider Than the Roll of Carpet
If your room is wider than the width of the carpet roll, you will need to have a seam (or several seams) running along the edge of your room. For example, if your room is 18’ by 20’, you will require extra carpet to fill in space beyond the width of the carpet.
Let’s say you choose a carpet that comes on a 12’ roll. For the above-sized room, you would buy a 12’ by 20’ piece of carpet, and then you would have 6’ by 20’ of room left to fill in.
The most cost-effective way to handle this situation is to purchase another piece of carpet that is half the length of the room. Why half? Well, since you have 6’ of room left to fill in, and your carpet comes in a 12’ width, you can cut the width in half (12 divided by 2), and use two pieces to fill in the remaining space. So, for this scenario, you would buy an extra 12’ by 10’ piece of carpet, which would then be cut in half to give you two pieces 6’ by 10’ each. These can then be laid end-to-end, to fill in the remaining space.
Closets have a bit more leeway in their requirements because they are often small and dark. Obviously, large walk-in closets should follow the same guidelines outlined thus far, because a change in pile direction will be just as noticeable as it would be in other areas. But for smaller closets, it's possible to get away with bending the rules.
If the closet is standard size (usually about 2'6" deep) and has a sliding door that is on a track, then the direction of the carpet is not as important, unless it is a patterned carpet. Because the track divides the carpet, it will not be noticeable if the pile is turned in the closet. This allows you to make use of some off-cuts from other areas, rather than having to purchase extra carpet for the closet.
Some carpets feature a pattern, either printed on the carpet like the one featured above or made from altering cut fibers with looped ones. If you have to join two pieces of patterned carpet together, you need to be sure that the pattern will line up on both pieces.
Manufacturers will list a size for pattern match on the back of the carpet sample. This is the extra amount of carpet you need to buy, to be certain that you will have enough to match up the two pieces of carpet. The amount required for pattern match is the size of the pattern – so for example, if you have a carpet that has a pattern consisting of 3” squares, then the extra amount of carpet you would need to buy would be 3”.
The amount for pattern match must be added on to every piece of carpet that will be seamed together, except for the first piece. This is because the installer will lay the first piece down, and then have to shift the next piece to get it to line up with the first.
Keep in mind that, depending on how you are seaming your carpet, you may have to add the pattern match to the width as well as the length. So, for the above example, you would need to add 3” to the length (if you are seaming two pieces of carpet on the side) and 3” to the width (if you are seaming two pieces of carpet on end).
Go With a Pro
As you can see, calculating the requirements for carpet can be a complex task, depending on the area being carpeted. This article is meant as a guideline only, to help you understand the process of figuring out how much carpet is required. If you have an unusual layout, are working with a pattern match, or are seeking to carpet several areas in your home, I highly recommend having a professional come in to do the measuring and calculating. Professionals will know what to look for, and can potentially point out some things you did not consider, such as placement of seams.
If you have stairs involved in the area to be carpeted, then calculating how much carpet you will need gets even more complicated. If you feel you have a good understanding of the process thus far, then move on to the next article, How to Measure and Calculate Carpet for Stairs.