Construction

Deck Board Spacing Calculator

Find an even deck-board layout that keeps both outside margins equal, then estimate linear feet, joists, and fasteners from the same board count.

Inputs

Adjust your numbers

Results update as you type.

Enter dimensions in inches. Use actual board width and subtract any picture-frame border from the deck width first.

Deck width across boards (in) (required) Measure perpendicular to the boards. Use the field width after subtracting borders or picture-frame boards.

Actual board width (in) (required) Use the finished face width: nominal 6 in decking is usually 5.5 in actual; nominal 4 in is usually 3.5 in.

Preferred gap (in) (required) Starting target for board spacing. The calculator may nudge it so both deck edges land symmetrically.

Deck length along boards (in) Used for linear feet, joist count, and fastener estimates.

Joist spacing on center (in) Typical values are 12, 16, or 24 inches on center depending on material and installation angle.

Fasteners per board-joist crossing Use 2 for two-screw face fastening or 1 for many hidden-clip systems.

Waste allowance (%) Adds extra linear footage for cuts, defects, and ordering buffer.

Results

Live answer

Boards across 25

Achieved gap 0.250 in (≈ 1/4 in)

Edge margin 0.250 in (≈ 1/4 in)

Board-start marks

Showing first 12 of 25. Every 5th board highlighted for tape-measure scanning.

#10.250 in (≈ 1/4 in)
#26.000 in (≈ 6 in)
#311.750 in (≈ 11 3/4 in)
#417.500 in (≈ 17 1/2 in)
#523.250 in (≈ 23 1/4 in)
#629.000 in (≈ 29 in)
#734.750 in (≈ 34 3/4 in)
#840.500 in (≈ 40 1/2 in)
#946.250 in (≈ 46 1/4 in)
#1052.000 in (≈ 52 in)
#1157.750 in (≈ 57 3/4 in)
#1263.500 in (≈ 63 1/2 in)
#1369.250 in (≈ 69 1/4 in)
#1475.000 in (≈ 75 in)
#1580.750 in (≈ 80 3/4 in)
#1686.500 in (≈ 86 1/2 in)
#1792.250 in (≈ 92 1/4 in)
#1898.000 in (≈ 98 in)
#19103.750 in (≈ 103 3/4 in)
#20109.500 in (≈ 109 1/2 in)
#21115.250 in (≈ 115 1/4 in)
#22121.000 in (≈ 121 in)
#23126.750 in (≈ 126 3/4 in)
#24132.500 in (≈ 132 1/2 in)
#25138.250 in (≈ 138 1/4 in)

Linear feet 440.0 ft

Joists 13

Fasteners 650

How it works

Enter your deck field width, actual board width, and preferred gap, then add the deck length, joist spacing, fastener pattern, and waste allowance if you want a material estimate. The calculator solves the number of full boards that fit, adjusts the gap so both outside margins match, and shows board-start marks along with linear feet, joists, and fasteners.