How Do I Calculate How Much Decking Do I Need?

This is one of the most commonly asked questions from every person who has a certain decking design on their mind. You need make your own decking calculator and figure out the surface of your future decking and express is in square metres.

Why is this important? First of all, it is what all your costs for your future decking are based on. The construction material is sold in that way, and the decking installation costs are calculated based on the surface that needs installing.

How Do I Calculate Decking Material?

First, you need to think about your decking design. Do you want a simple rectangle floating decking that doesn’t have any connection to the house? Will one side of your decking be leaning on the front of your house? What is the shape of your decking? What will be the length of the sizes of your decking?

It is best if you try and draw your decking and then measure the space to have the idea about the decking measurements. If you plan on making a square or a rectangle decking, your decking calculator will be easy. Simply multiply the width of your decking with the length. For example:

The surface of the rectangle decking is a x b = 3 m x 1.5 m = 4.5 m2

Square is even easier. You just multiply the value of one side. In this case a x a = 3 x 3 = 9 m2

If you have an L shaped decking, you just need to break it down to shapes that are easy to calculate. This is very easy if your decking can be turned into squares and rectangles, like this:

In this case you need to turn this surface into two surfaces. The smaller one is c x d. The larger one has one side which is a and another side which is e.

Therefore, the larger area is a x e = 1.5 m2 and the smaller area is 2 x 1.5 = 3 m2. When you add these two together you get 4.5 m2.

So far it is all easy. Some more serious calculations begin when you want to calculate some irregular shapes. You may want to do this yourself and you may want to leave that to a professional.

Either way, with these calculations, you will get the area that needs to be covered with your decking.

How Do You Work Out Linear Metres?

Linear metres are important for you because that is how you’ll probably buy your decking timber. To calculate that, you need to know the width of your boards and to determine the spacing between them.

As a rule of thumb, your decking boards should be around 3 mm apart. You should also calculate 10% of wastage.

You get linear metres by dividing your square metres with the width of one decking board plus the 3 mm gap. Check that with the manufacturer, but they usually come in the width of 64mm, 86mm, 130mm and 135mm.

Let’s say you are making that rectangle timber decking from above. It is 3 x 1.5 m. That is 4.5 m2.

Now let’s assume that you are using the 86 mm board. That is 0.086 m. If we add the 0.03 gap, we will get 0.089.

This means that for the 4.5 m2 decking, you need 4.5 m2 / 0.086 m which is 52.3 m. Let’s add 10% to it to calculate the waste in, as well. This brings us to 57.5 m.

Let’s say that your boards are 1.2 m long. This means that you need 49 boards that are 8.6 cm x 120 cm for your decking cover.

However, the decking boards are not the only material that you need to make your decking. You need joists, fixing and bracing.

How Many Joists Do I Need for a Deck?

When calculating your decking surface, keep in mind that it is best to place your joists around 450 mm apart. Again don’t forget to calculate the width of your joists and don’t use joists that are more than 1.2 m long. Longer joists will create that bouncy feeling when you walk over your decking.

Screenshot source: Meyer Timber

Your joists don’t have to be of the same material like your decking cover. Also, you need to include the bearers, ledgers and posts. They can be timber or even treated pine, but in that case they need to be at least H4 and H5. Planning and calculating this structural timber is a task for a professional.

When you plan on the stirrups, bolts, screws and nails, as well as the hangers, plates and other fixings, make sure that they are hot dipped galvanised. They need to have protective coating or to be made out of stainless steel.

Of course, there is the matter of pouring the concrete basis for the pillars on which the entire construction will rely. While a couple of concrete blocks, some nails and screws aren’t expensive, these little things add up easily and ramp up the price of your decking. Therefore, you need to keep your eye on them, as well.

Your decking calculator should include all the decking, structural timber, fixings, concrete blocks and any additional elements of your decking. If you want roof, stairs or fence, all those items are calculated into your final cost.

The last, but not the least is the price of labour. While there are those decking installers who charge by the hour, the majority of them in Australia, charge by the square metre of the decking installed.

When negotiating, you need to make sure if the price you are getting is the price with or without the material. That is the only way you will be able to calculate the budget.

You can ask your decking installer to give you the estimate in material, as well. How many nails and screws do they need approximately. You don’t need to know the exact number, just learn whether that is something within the ballpark of $50 or $100.

Then, you can negotiate the price of labour. The best way not to overpay your decking project is to get several quotes and see how much you should pay, what is too much and what is too little.

Ask for precise quotes from Australian decking professionals and pick the best one for your project.