How To Calculate Linear Feet: The Easy Way


You may have noticed that a square foot is not the same as a linear foot (also known as lineal feet) when browsing DIY material online.

A linear feet is a measurement of length, regardless of how wide a material is, while square feet refers to the number of symmetrical portions of 1 foot width by 1 foot length found within an area you want to measure. 

Essentially, these measurements (linear feet and square feet) provide two different ways to calculate the amount of material needed for an area, and their calculations are influenced by the shape of the area, be it a floor, wall, or ceiling.

Here are some tips for determining the linear feet of building materials and how to determine the precise area of a floor or deck especially where things are not nicely rectangular or square.

So for example, if you want to know how much decking you need for your decking project. You could do the math yourself or use a linear foot calculator online. Which approach you choose depends on how complex your project is! Some find it much easier than doing math by hand, especially with more complex scenarios. If you want a more comprehensive analysis of the total likely cost, then this is the way to go.

The 3 Question Approach Of How To Calculate Linear Feet

Here is a quick and dirty DIY approach that will work for most situations where you want to know the Linear Feet amount for a material to cover a certain area square or rectangle area. If you have a project with more than one square or rectangle area, just break it up into a set of sub-areas, and use the method for each sub-area and add everything together at the end. So for a given square or rectangle sub-area, it comes down to 3 very simple questions:

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Question 1: What is the square footage of the material you need to cover?

Lets call this ‘A’.
Square Feet are calculated by multiplying the width by the length of the area you want to cover. Typically, it is the floor of a bedroom or the ceiling of a room. It doesn’t matter. Simply multiply the length by the width to get a square foot value.

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Question 2: What is the width of the material you want to cover with?

Lets call this ‘B’. It needs to be in feet.
If it is a carpet roll, it may be 12 feet wide. It may be a tongue and groove hardwood board that is 6 inches wide (converted to 0.5 feet for the 3 question calculation so it remains in feet). 

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Question 3: What is ‘A’ divided by ‘B’?

We’ll name this ‘C‘.
No matter how wide your material is, ‘C’ is the length (linear feet) of material you must use to cover the area.
Most of the time, it really is that simple. Now we explain why there are some caveats – sometimes.

Caveats To The 3 Question Approach

So usually, the three-question approach is all you need to determine how many linear feet of material you need to cover a given area. But as with anything in life, there are a couple of quick caveats to consider:

Caveat 1 – Aesthetics:

You may not have your answer quite yet if you don’t want to patch the material. It is less of an issue with hardwood floors and decks but is more of a concern with wide materials like carpet or vinyl.

When planning the aesthetics of a material such as a carpet lay for example, if you have a 16 by 20 foot room, and your carpet is 12 feet wide, you might prefer to have two pieces of carpet joined right down the middle to keep everything nicely symmetrical. To do it this way, you would need two pieces at 20 feet length which would be more costly, instead of getting just 26.6 linear feet. The 26.6 linear feet approach is less costly but you will have a patchwork approach with multiple pieces and joins being necessary.

Caveat 2 – Gaps Between Decking Boards

In addition to accounting for width when calculating decking materials, you should also make sure you account for the space between each length of decking board. In order to determine the overall linear feet of the decking material you want to use for the job, you need to add the width of the gap between boards when coming up with the answer to Question 2.

Caveat 3 – Allow For Wastage

Finally, remember that there is also natural wastage of any material you use for a project. Typically you need to add an additional 5% to 10% to the final quantity to account for this.

In Conclusion

So to reveiw, there are two ways to do the calculations:

  • You can use an online linear foot calculator to figure out the linear feet of materials you need for your next project.
  • For a simple rectangular area you want decking material for, you can use the simple 3 question approach.

The good thing about the standardized way to measure such building materials in linear feet is that you don’t need to worry about the width of the decking board materials once you’ve done the calculations – so regardless if you choose 4-inch decking boards or 6-inch boards, you’ll still be talking apples and apples when you discuss with the supplier how much you need for the project.

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