1. Deck dimensions
Boards are assumed to run along the length; joists run across the width. These are quantity estimates, not a structural design.
2. Decking boards
Confirm board spacing and end-joint rules with the board manufacturer. If stock boards are shorter than the deck, additional support at joints may be needed.
3. Joists and fixings
Joist spacing is an editable assumption, not a recommended structural specification. Fixings estimate assumes screw-fixed boards; hidden-clip systems differ.
4. Your prices
Example prices only, not live quotations. Excludes supports, posts, beams, groundworks, balustrades, fascia, labour and any additional fixings.
Your decking estimate
Boards
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Joists
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Fixings
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Estimated materials + delivery
Based on your editable prices
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Before ordering: Check the manufacturer's board gap, fixing method, support at board ends and joist joints, structural spans, ground conditions, drainage and any building or planning requirements. This is not a deck design or complete bill of materials.
Printable shopping list
How to calculate decking boards in the UK
Measure the deck length and width in metres. Choose the direction the boards will run. The calculator assumes boards run along the length, then divides the width into board rows using the selected face width and gap.
Worked example: 4 m × 3 m
With 145 mm boards and 5 mm gaps, 20 rows span 3 m. A 4.8 m stock board can cover each 4 m row, so that is 20 boards before allowance, or 22 with a 10% extra allowance.
What about the joists?
For a simple quantity illustration, 400 mm centres along a 4 m length give 11 joist lines. Each line crosses the 3 m width. The actual structure, joints, supports and span limits must be designed separately.
Frequently asked questions
Can I use shorter boards?
Yes, but butt joints may need dedicated support and a staggered layout. This estimator counts full stock lengths per row; it does not optimise offcuts or design joint support.
Does this include the full deck frame?
No. Joist quantities are illustrative only. Bearers, beams, posts, noggins, foundations, connectors, steps and railings are not included.
Are the example joist centres suitable for my deck?
Not necessarily. Confirm spacing and span requirements for your chosen board and structural timber, load, ground and local conditions.
Can I print my shopping list?
Yes. Use the print button to print or save a PDF using your browser's print function.