How to calculate deck boards needed for a job...

Updated: Apr 2

To calculate how many deck boards you will need for a job is relatively simple to do. The first thing that you would need to determine is direction that your decking is going To be running on your deck. You will want to measure the distance that is perpendicular to the direction your boards are running.

e.g If your deck boards are running parallel to your house, you would measure the distance from the house to the outside edge of your deck.

It is important to remember that the lengths of the deck boards available are in 12’,16’ and 20’ lengths. You will want to pick the length that is closest to what your deck size is to minimize waste. If you have a very large deck over twenty feet or more, you will need to get creative and add a breaker board. A breaker board simply divides your deck into sections and is perpendicular to the actual decking direction that you chose.

e.g a deck that is 32’ long will need a breaker board in the middle of the deck and you will use 16’ deck boards.

To calculate the amount of deck boards needed:

1) Measure the distance perpendicular to the direction of the decking direction. Let’s say that distance is 12‘. Take the 12 foot measurement and multiply that by inches(12)=144” total. You will gap your deck boards so that gap will be included in the conversion.

Length of area perpendicular to decking/board width plus the gap

Example #1

1.) 144”(overall width) (divided by /)(5.5”(deck board width)+(.25” gap))

2.)144”/5.75”=25.04 boards needed. You will always want to round this number up. In this case 25 boards will be sufficient. If you calculation was 25.5 you would want 26 boards.

Example #2 (Deck that is 24’ long and decking is parallel to the house)

1.)23’x12”=276” then divide 276” by 5.75(deck board width plus gap)

276”/5.75= 48 boards total

The same measurements will be used if the decking is running perpendicular to the house you will calculate the measurements the same way.

To calculate the amount of deck fasteners you would need.

1.) Stowaway hidden fasteners- Calculate the total square foot size of your deck and multiply that number by 1.5(stowaways per SQFT) E.g. a 200 square foot deck multiplied by 1.5 = 300. You will need approximately 300 stowaway hidden fasteners.

To calculate how many stair tread boards you would need

1.) Measure the width of the stair tread (4 feet is very common and is code in many places. Please check your local building codes and guidelines) you will need to boards that are (5.5”+0.25” gap)= 5.75” multiply this by 2 to get close to a 12” stair tread (11.5” wide stair tread)

To calculate the amount of Fascia you will need

Measure the perimeter of your deck and and any sets of stairs that you may have. If your deck is attached to the house or free standing very close to the house you do not need to include that measurement.

If you have a 12’x14’ deck with a set of 4 steps coming of the deck, this is how you would calculate the fascia.


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