Deck Board Calculator
Count the deck boards, linear feet and joists for a rectangular deck.
Calculator
| Board rows | 26 rows |
|---|---|
| 12 ft boards (before waste) | 26 boards |
| 16 ft boards (before waste) | 26 boards |
| Joists at 16 in on center | 10 joists |
How it is calculated
A 5/4×6 board is about 5.5 in wide plus a 1/8 in gap = 5.625 in per row. 12 ft × 12 ÷ 5.625 = 26 rows of 12 ft = 312 linear feet; +10% = 343 ft.
About this calculator
Deck boards run in rows across the joists. A common 5/4 × 6 board is about 5.5 inches wide, and a small gap is left between boards for drainage, so each row takes about 5.625 inches. The calculator counts rows, linear feet and how many 12- or 16-foot boards that makes.
Choosing board lengths that land on joists reduces waste. Stairs, fascia and borders take extra boards, and diagonal patterns need more.
Worked examples
| Project | Linear feet of 5/4×6 decking (+10%) | Rough cost |
|---|---|---|
| a 12x12 ft deck with 5/4×6 boards | 343 ft | $515 – $2,059 |
| a 10x16 ft deck with 5/4×6 boards | 385 ft | $578 – $2,310 |
| a 16x20 ft deck with 5/4×6 boards | 757 ft | $1,135 – $4,541 |
| a 20x24 ft deck with 5/4×6 boards | 1,144 ft | $1,716 – $6,864 |
Buying notes
- Board spacing depends on the material; follow the manufacturer's guidance for the gap.
- Add boards for stairs, fascia and any picture-frame border.
- Deck screws, joist hangers and railings are not included.
Quick answers by size
Click a size for the exact quantity and cost.
How to measure and use this calculator
- Measure the deck's length (the direction the boards run) and its width.
- Read the number of board rows and the linear feet required.
- Pick board lengths that fit the deck with the least waste.
- Check joist spacing against the decking manufacturer's rules.
Common mistakes
- Leaving out the gap between boards in the row count.
- Ignoring stairs and fascia boards.
- Choosing board lengths that leave short cut-offs.
Tips
- Standard 5/4×6 deck boards are actually about 5.5 inches wide.
- Plan board lengths to land on joists and minimize waste; 12 or 16 ft boards are common.
- Joists at 16 inches on center suit most composite and wood decking, but follow the manufacturer's spacing.
Frequently asked questions
How many deck boards do I need for a 12x12 deck?
About 26 rows of 12 ft boards, roughly 28–29 boards with waste.
How wide is a 5/4×6 deck board?
About 5.5 inches in actual width.
How many deck boards for a 12x12 deck?
About 26 rows of 12-foot boards, roughly 28 or 29 boards once you add waste.