Finished Raised Deck

Weed Fabric

Laying Your Joists

Installing Decking Boards


Maximize Your Outdoor Space with Our Decking Calculator

At Kelvin Timber, we understand the value of a beautiful deck in enhancing your garden. That’s why we provide complete decking kits that are quick and easy to assemble, perfect for creating a simple, flat deck. With our decking calculator, you can effortlessly input your desired decking dimensions, length, width, and preferred joist width, and we’ll ensure you have everything you need to bring your dream deck to life.

Our kits are supplied flat-packed and ready to build, though some cutting may be required. Instructions for assembly can be downloaded below for your convenience.

What’s Included in Your Kit?

  • All the decking boards necessary for your project
  • Framing timber to construct the substructure
  • Screws required for a safe and secure installation
  • Weed fabric to lay beneath your deck, helping to prevent weed growth
deckplan This calculator uses the following specifications:
With your Decking: Maintain 5mm gap between deck boards for expansion.
With your Joist: This calculator works out the joists at 500mm centers.
Description Quantity Price Each Total Price
Weed Fabric- 14m x 1m = 14m2
Decking Screw PZ2 4.5m x50mm (box of 200pc)
Sub total exVAT
Grand Total

Decking Extras and Facia Boards

If you find yourself in need of extra boards or facia for your decking project, simply add your desired deck kit to the cart and proceed to the basket page. There, you'll have the flexibility to adjust quantities as needed to accommodate any additional materials required.

For any decking extras or facia boards, please refer to the options below

How To Calculate A Decking

How to calculate the area of the deck, if your size doesn’t match our calculator:

Multiply the length by the width to get the total area.

Determine the number of deck boards:

Divide the total area by the area covered by one deck board (including the 5mm gap).
Round up to the nearest whole number since you can’t have a fraction of a deck board.
Calculate the number of carcassing:

Determine the number of joists required based on the size and spacing.
Adjust the number based on the length and width of the deck.
Estimate the quantity of screws:

Determine the number of screws based on the number of deck boards and any additional structural elements.

Find the area of weed fabric:

Match the area of the weed fabric to the area of the deck.

Example Calculation

Let’s perform these calculations for a sample deck size (3.6m x 3.6m):

Area of the deck:

Area = Length x Width
= 3.6m x 3.6m
= 12.96 square meters
Number of deck boards:

Area covered by one deck board = (3.6m – 0.005m) * (3.6m – 0.005m) (to account for the 5mm gap)
≈ 12.59 square meters
Number of deck boards = Total area / Area covered by one deck board
= 12.96 square meters / 12.59 square meters
≈ 1.03 (rounded up to 2 boards)
Number of carcassing:

Based on standard spacing of 500mm, you would typically need approximately 8 to 9 joists for a 3.6m span. We’ll assume 9 for this calculation.
Estimate screws:

Depending on the design, you might need around 2 screws per deck board, so for 2 boards, we’ll estimate around 4 screws.
Weed fabric:

The area of the weed fabric would match the area of the deck, which is 12.96 square meters.

Joists for Your Decking Project

When it comes to constructing a sturdy and reliable deck, choosing the right joists is crucial. Our decking calculator offers several options tailored to different project needs.

Let’s delve into what each option entails and how to make the best choice for your project.

Joist Spacing:
It’s important to note that our calculator works out the joists at 500mm centers. This spacing ensures optimal support and distribution of weight across the deck structure, enhancing its stability and longevity.

100mm Joists:
These joists are ideal if you’re not raising your deck off the ground significantly. They provide ample support and stability for your decking boards while keeping the structure close to the ground. If your deck doesn’t require extensive load-bearing capabilities or if you’re working within height constraints, 100mm joists are an excellent choice.

125mm Joists:
For projects where load-bearing capacity is a priority or if you prefer a bit more clearance from the ground, 125mm joists are the way to go. These joists offer additional strength and resilience, making them suitable for decks that will bear heavier loads or decks that need to be elevated further off the ground. Choosing 125mm joists ensures added durability and peace of mind, especially for larger or more complex decking projects.

150mm Joists for Raised Decks (not added to calculator yet):
If you require significant elevation for your deck, we recommend opting for 150mm joists. These joists provide the necessary support and stability for decks raised off the ground, ensuring structural integrity and longevity. Whether you’re building a raised platform, a multi-level deck, or simply prefer a higher clearance, 150mm joists offer the robustness needed for elevated decking projects.

Considerations for Selection:

  • Load Bearing: Assess the intended use of your deck and the potential weight it will bear. If you anticipate heavy furniture, foot traffic, or other significant loads, opting for 125mm or 150mm joists is advisable.
  • Height Requirements: Evaluate how high you want your deck to sit above the ground. While 100mm joists are suitable for lower elevations, 125mm and 150mm joists provide more clearance if desired.
  • Personal Preference: Some individuals simply prefer the added robustness and stability that larger joists offer, regardless of specific project requirements.

Whether you choose 100mm, 125mm, or 150mm joists, rest assured that each option is designed to meet your decking needs. Selecting the appropriate joist size ensures that your deck is not only functional and resilient but also tailored to your specific preferences and project requirements.

Decking Board Details

Our decking boards are supplied in lengths that are tailored to fit your project seamlessly. Each board is calculated to cover 150mm, comprising 145mm for the board itself and a 5mm gap allowance for expansion and contraction. This thoughtful design ensures not only an aesthetically pleasing appearance but also accommodates the natural movements of the wood, enhancing the longevity of your deck.

Additionally, all screws necessary for installation are included with your decking purchase, eliminating the need for separate sourcing and ensuring a hassle-free installation process.


Delivery Information

For our valued customers in the West of Scotland, we offer local delivery services to ensure your decking kit reaches you promptly and efficiently. We offer Delivery Options Expedited, Standard & Free Delivery over £750.

Outside the West of Scotland?

If you reside outside our local delivery area, don’t worry! Simply send us a message, and our team will be happy to assist you in arranging delivery. We’ll work with you to determine the best delivery options, costs, and timescales for your location. Fill out form and one of our team will get back to you soon