How much is…..?

“How much is it going to be to”…?

“Can you give me a price for”….?

“What’s it likely to cost me to”…?

These are the things at Forestrall Timber and Fencing Merchants we hear again and again throughout our day…  And it’s music to our ears!  Quoting prices for timber and fencing is what we do best, and with such a wide range of stock we’re able to be competitive and provide our clients with what they need.

However, there are two types of call….

“How much is it going to cost me to put an area of decking in my garden, in the far corner, fairly big but not too big?”


“How much is it going to cost me for 200 deck boards, preferably around 145mm width?”

As you can imagine, the second question is far easier to assist with!

With any project, it’s all about the planning.  As the saying goes – fail to plan, plan to fail!

Calculating decking is quite straightforward and if you remember to measure twice then you shouldn’t have problems. Below is how we would suggest measuring a space and then calculating the deck boards required.

In many instances the decking area is rectangle and as such the two basic dimensions are the width and the length. When measuring it’s easy to make a mistake, and when calculating an area this mistake is compounded. So always remember Measure Twice.

We use metric measurements when measuring and it really is simple. Measure the width and the length and jot down the measurements : i.e.: width = 3.15 metres or 315 cm and the length 4.85 metres or 485 cms. To calculate the area just multiply width x length.  Area = 3.15 x 4.85 = 15.3 sq.metres (rounded up).

If your decking area is more than just a basic rectangle then multiply the width times the length of each section for the total square metreage of each section and add the square metreage of each section together.

For example, a deck with a main portion of 4 by 5 metres with an additional section that is 3 by 3 metres, the square metreage of the main section is 20 square metres and the square metreage of the additional section is 9 square metres. In this example, the total square footage is 29 square metres.

Look up the specifications for the length and actual width of deck boards you will use for decking.

You will often find that decking is sold per linear metre and so a calculation is required to convert square metres to linear metres which can, on first impressions, seem rather complicated.

It helps to think in terms of the number of linear metres required to cover an area of 1 square metre, (1m x 1m).

To calculate this, first assume that the 1m ‘length’ of the area is always covered by 1m long decking boards.

Then, establish how many boards need to be laid side by side to cover the areas 1m ‘width’.

Always allow 5mm for spacing alongside each board, so assume a 140mm wide decking board provides 145mm width of face coverage.

Given that the total width of the area to be covered is 1m (or 1000mm), a total of 6.9 boards are required, (1000mm ÷ 145mm).

If these boards are laid to end, they would provide a total linear metre run of 6.9 – the amount required to cover a one square metre area.

This ratio can be used to calculate the linear metre equivalent of any m2 area being covered by a 140mm wide board and vice versa.

For instance:
50 square metres x 6.897 = 344.85 linear metres
100 linear metres ÷ 6.897 = 14.5 square metres


A simple formula can be used to establish the conversion ratio for any width of decking board:

Conversion ratio = 1000 ÷ (width of board in mm + 5mm)

Some common examples, rounded to two decimal places:

90mm Board = 1000 ÷ 95 = 10.53
115mm Board = 1000 ÷ 120 = 8.33
130mm Board = 1000 ÷ 135 = 7.41
140mm Board = 1000 ÷ 145 = 6.90
145mm Board = 1000 ÷ 150 = 6.67

There is a handy chart available on the QDeck site, which will help when estimating your decking requirements.

Don’t forget that it’s best to add 15 percent more boards for miscuts and miscalculations if the boards will be installed at 90 degrees and add an additional 15 percent more for deck boards that will be installed on a diagonal pattern. Round up to the nearest whole number and add that to the number of deck boards.  For example, if you’ve worked out that your area for decking requires 128 deck boards, then adding 15 percent for a 90 degree installation will add 20 more boards and another 15 percent for a diagonal pattern will add a cumulative 42 boards.

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