Project estimating guide
Deck Board Width, Gap and Count: A Worked Example
Deck boards cover width in repeating rows separated by gaps. Use actual width and the specified edge gap, then check whether each row can be supplied by one stock board or needs more.
Reviewed September 6, 2026Count gaps between boards
For N boards, the covered width is N × board width + (N − 1) × gap. Solving for N gives round up((deck width + gap) ÷ (board width + gap)).
12 ft width and 5.5 in boards
Use the gap specified for your actual product and conditions.
| Illustrative edge gap | Board rows |
|---|---|
| 0 in | 27 |
| 0.125 in | 26 |
| 0.25 in | 26 |
Stock length changes the purchase
At 16 ft deck length, 26 rows can use twenty-six 16 ft boards before allowance. If using 12 ft stock without sharing offcuts, each row requires two boards: 52 before allowance. An optimized supported layout could differ, but total linear footage alone would hide the cutting problem.
Check the real installation layout
Actual board width differs from some nominal lumber labels. End gaps, supporting joists, temperature effects, borders, stairs, and diagonal patterns can also change the takeoff. The calculator estimates straight surface boards; it does not size structural framing or approve unsupported joints.
Sources and product references
- Trex — deck board spacing
Board spacing depends on the product and installation method.