How to Calculate How Many Decking Boards I Need

Will a Composite Decking Board Rot?

How to Calculate How Many Decking Boards I Need

• M. John
• July 18, 2021
• Installation

Ensuring you get your decking board calculations correct is important. If you want to build a deck using composite decking boards, you will need to know the number of boards required to complete your project and help to determine how much you need to budget.

If you don’t know how to calculate how many composite decking boards you will need, reviewing this article will help you.

Calculating Your Decking Boards

The simplest way to determine how many decking boards you will need is to calculate it yourself or use an online decking calculator. However, some other factors need to be considered to determine the exact number of boards needed.

You will need to know the square meterage of your decking area and also consider how the design layout of your decking could affect the number of decking boards you will need. Don’t forget to add 5% to 10% for wastage if your decking design is complex or includes diagonal or curved shapes and multiple cuts. You will also need to know the size of the composite decking boards you plan to use.
You can use a calculator to calculate the number of decking boards you need. The first step to take if you want to calculate the number of composite or wood decking boards for making your deck is to determine your deck size. How large do you want your deck to be? Do you want it small or big? Estimate the dimensions of your deck to know its size.

Use a tape measure to discover the length and width of your deck. Once you know the length and its width, multiply both together to determine the deck area.

Decking Board Length

Next, you also need to know the lengths of the decking board you want to use. Most wood and composite decking boards have different board lengths that range from 2.4m, 3m, 3.6m & 4m. The widths of composite decking boards range from 120mm up to 160mm and wider. Once you get the board length you want, choose your joist spacing. Most domestic joist spacings are 30cm (300mm) to 40cm (400mm) in the centre, depending on whether your decking is for residential or commercial use. For commercial use, place joists centres at 20cm (200mm) to accommodate for the additional footfall and weight. This should be checked with the composite decking manufacturer or supplier.

You should always check with your local authority for any building regulations to determine adequate spacing required for your decking joists.

Steps to Calculate the Number of Decking

You can calculate the number of decking boards you need for your deck project in three simple steps. You will need a jotter, pen and a calculator.

Step 1 – Estimate the Deck Area

Multiply the length and width to calculate the total size of the decking area.

Step 2 – Calculate the Board Area

Knowing the total area of your deck, proceed to find the total area of the decking board you want to use. You have to multiply the board length together with its width in centimetres or metres.

For instance, if the length of your decking board is 360 cm (3.6m) and the width is 15cm, multiply by each other to give you the area of your decking board.

Step 3 – Calculate the Boards

You can now calculate how many decking boards you will need since you have your deck and board area. To find the number of decking boards you need, divide the total deck area by the board. Your result is the number of decking boards you will need to complete your decking project. However, it’s advisable to purchase extra decking boards to account for waste. In addition to that, it is also good to purchase extra fasteners for your decking.

For example: A total deck area of 5sqm x 4sqm = 20sqm

You will then work out the board’s sqm value by converting all to millimetres. To do this, multiply the length of the board by 1000; for example, if you have a 3.6m board, this = 3600mm. You then multiply the width of the board by mm, which a high percentage of board dimension will already be quoted in millimetres.

For example, Ultra Decking’s home choice premier is 3.6m by 140mm, which would be 3600mm x 140mm Multiplying these together = 504,000 sqm, then divide by 1 million, which will give you the board’s sqm value which in this instance is 0.504sqm. Always round up, even if you do not have a single number.

Then lastly, you can calculate by taking the sqm area of 20sqm and the board’s sqm value of 0.504 and then dividing.

20/0.504 = 39.68, always round up providing 40 boards; please note this does not include wastage, and it’s always advisable to add wastage of 5 % to 15% with designs requiring unique shapes and cuts.

Decking Board Width

The next method of calculating how many decking boards you will require is using the width of the boards. Again convert width to mm if not already provided. With this example, we will use home choice premier again at 140mm width.

Convert the metres to millimetres by multiplying by 1000. With this method, you need to convert to mm where the boards are running the width of the decking; For example, if your boards are running parallel to the 5m area, the boards will run the width of the 4m, so covert this to mm which x 1000 = 4000mm

Now you are almost ready, don’t forget the clips; if you are using 3mm, clips add 3mm to each 140mm board width.

Now you ready 4000mm divided by 143mm = 27.97 always round up = 28

Now covert to linear metres. 28 x the length 5m = 140 linear metre then / (divide by 3.6 boards length) = 38.888 =39 boards

These are the two ways of calculating. In our experience, the first option is always the best unless you have an exact width, like 4m or 5m, etc.

Conclusion

If you want to build a deck, it is good to calculate how many decking boards you will need. Follow the simple steps in this article to calculate the number of decking boards needed for your next project.

Also, check out Do You Leave Gaps Between Composite Decking Boards