A worked calculation you can check
- 01
Write the measured scope
Deck Boards for a 16 × 20 Deck begins with a visible, checkable scope: Deck field: 16 ft wide × 20 ft running length; Board module: 5.75 in; Stock boards: 16 ft; 10% allowance. Keep the units beside every dimension so feet, inches, square feet and purchase coverage cannot be mixed silently.
- 02
Run the unrounded arithmetic
The 192 in width needs ceil(192 ÷ 5.75) = 34 rows. Those rows contain 34 × 20 = 680 linear ft; 680 ÷ 16 = 42.5 stock boards, and 10% raises that to 46.75.
- 03
Convert to complete stock-length deck boards
Round to 47 sixteen-foot boards as a linear-foot starting point, then create an approved joint layout. Offcuts cannot be assumed reusable without mapping stagger, joists and fastener zones. Round only after the final division, then reconcile the number with the sizes or increments the supplier actually sells.
- 04
Test the result against the real project
A breaker board or different stock-length mix may produce a cleaner, more buildable result than repeating butt joints across the 20 ft run. Use actual board width, installation gap, running direction, stock length and an approved joint or breaker-board plan for the selected product.
Worked inputs and arithmetic
Calculate a 20 ft board run across 16 ft of width when only 16 ft stock boards are used.
The 192 in width needs ceil(192 ÷ 5.75) = 34 rows. Those rows contain 34 × 20 = 680 linear ft; 680 ÷ 16 = 42.5 stock boards, and 10% raises that to 46.75.
- Deck field: 16 ft wide × 20 ft running length
- Board module: 5.75 in
- Stock boards: 16 ft; 10% allowance
What can change this answer
A breaker board or different stock-length mix may produce a cleaner, more buildable result than repeating butt joints across the 20 ft run.
Deck-board arithmetic does not design framing, footings, guards, stairs, connections, permits or structural loading.
- Composite butt-joint gaps and supports are product- and temperature-specific.
- A diagonal field increases row length and edge waste beyond this parallel model.
- The final narrow row may need ripping and cannot always consume ordinary offcuts.
Turn the example into your own order
Open the Decking Calculator, enter the dimensions from your site and replace the example coverage, yield, density, waste, package size or capacity with the exact value that applies to your deck-board quantity choice. Save the first measured result before testing alternatives so the reason for every change remains visible.
Use actual board width, installation gap, running direction, stock length and an approved joint or breaker-board plan for the selected product. Deck-board arithmetic does not design framing, footings, guards, stairs, connections, permits or structural loading.
What usually throws the order off
- Copying the deck boards for a 16 × 20 deck result without matching all three inputs
- Rounding every dimension before the deck-board quantity calculation
- Ignoring the buyable complete stock-length deck boards after the arithmetic
- Using extra deck-board quantity as a substitute for the site and product checks
Frequently asked questions
Can I use the deck boards for a 16 × 20 deck answer for a slightly different project?
Use it only as a reasonableness check. Enter your own dimensions and assumptions in the Decking Calculator; small changes in depth, height, repeat, pitch, coverage or capacity adjustment can alter the rounded purchase unit.
Why does the final number round up?
Complete stock-length deck boards are not normally purchased as the exact decimal produced by division. Round the final requirement to the next available unit, then document any remaining matching stock instead of hiding it as vague waste.
What should I verify before buying?
Use actual board width, installation gap, running direction, stock length and an approved joint or breaker-board plan for the selected product. Also verify this project boundary: Deck-board arithmetic does not design framing, footings, guards, stairs, connections, permits or structural loading.
Technical references
These references support the measurement and planning method. Product instructions, the site and applicable local requirements control the final installation.