A 3 ft (36") deck railing between posts takes 7 wood balusters (1-1/2") at 3-3/16" gaps or 8 metal balusters (3/4") at 3-5/16", both under the IRC 4" sphere. Hook the tape on the post once: the first wood edge goes at 3-3/16", the next at 7-7/8", then every 4-11/16".
36" between posts
Hook the tape on the post face once and mark every baluster edge from there; each mark is rounded once, so a 1/16" never compounds down the rail.
| Done | # | Mark | Tape | Centre | Decimal |
|---|---|---|---|---|---|
| 1 | Leading edge | 3-3/16" | 3-15/16" | 3.188" | |
| 2 | Leading edge | 7-7/8" | 8-5/8" | 7.875" | |
| 3 | Leading edge | 12-9/16" | 13-5/16" | 12.563" | |
| 4 | Leading edge | 17-1/4" | 18" | 17.250" | |
| 5 | Leading edge | 21-15/16" | 22-11/16" | 21.938" | |
| 6 | Leading edge | 26-5/8" | 27-3/8" | 26.625" | |
| 7 | Leading edge | 31-5/16" | 32-1/16" | 31.313" |
4x4 posts at 39-1/2" on centre: inside the 6'-0" AWC DCA 6 guard-post limit.
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| 7 | 3-3/16" | 4-11/16" | 3-3/16" | 8 | ||
| 8 | 3-5/16"+ | 4-1/16" | 3-5/16" | 9 | ||
| 7 | 3-5/8" | 4-5/8" | 3-5/8" | 8 | ||
| 5 | 3-1/16"+ | 6-9/16" | 3-1/16" | 6 |
| 1 | 3-3/16" | 3-15/16" | 3.188" |
|---|---|---|---|
| 2 | 7-7/8" | 8-5/8" | 7.875" |
| 3 | 12-9/16" | 13-5/16" | 12.563" |
| 4 | 17-1/4" | 18" | 17.250" |
| 5 | 21-15/16" | 22-11/16" | 21.938" |
| 6 | 26-5/8" | 27-3/8" | 26.625" |
| 7 | 31-5/16" | 32-1/16" | 31.313" |
Every baluster is 4-11/16" on centre after the first.
| 1 | 3-5/16"+ | 3-11/16"+ | 3.333" |
|---|---|---|---|
| 2 | 7-7/16"− | 7-13/16"− | 7.417" |
| 3 | 11-1/2" | 11-7/8" | 11.500" |
| 4 | 15-9/16"+ | 15-15/16"+ | 15.583" |
| 5 | 19-11/16"− | 20-1/16"− | 19.667" |
| 6 | 23-3/4" | 24-1/8" | 23.750" |
| 7 | 27-13/16"+ | 28-3/16"+ | 27.833" |
| 8 | 31-15/16"− | 32-5/16"− | 31.917" |
Every baluster is 4-1/16" on centre after the first.
05 / Field guide
This sheet lays out a 3 ft (36") deck railing between post faces. It compares 1-1/2" wood with 3/4" metal, gives every mark from one hook of the tape, and checks the 4" sphere rule and post spacing.
36" ÷ (1-1/2" + gap) fits 7 balusters with 8 equal gaps of 3-3/16" (3.188"), 4-11/16" on centre.
From the post face the leading edges fall at 3-3/16", 7-7/8", 12-9/16", 17-1/4" and on in 4-11/16" steps. Buy 8 to allow 10% for splits and miscuts.
Thinner balusters need more of them: 8 at 3-5/16"+ gaps, 4-1/16" on centre. The first four marks: 3-5/16", 7-7/16", 11-1/2", 15-9/16".
1" metal or composite takes 7 at 3-5/8"; 3-1/2" flat pickets take 5 at 3-1/16".
With 4x4 posts the centres are 39-1/2" apart, inside the 6'-0" DCA 6 limit for guard posts.
The guard top sits at least 36" above the deck and the bottom rail less than 4" above it.
Questions
7 of 1-1/2" wood or 8 of 3/4" metal for 36" between posts, centred with equal gaps. Buy about 10% more.
3-3/16" clear between 1-1/2" balusters (4-11/16" on centre) or 3-5/16" between 3/4" balusters (4-1/16" on centre).
Its leading edge sits one gap from the post face: 3-3/16" for 1-1/2" wood or 3-5/16" for 3/4" metal.
No. On 4x4 posts the centres are 39-1/2" apart, within the 6'-0" AWC DCA 6 limit.
7 at 3-5/8" gaps; 3-1/2" flat pickets take 5 at 3-1/16".
Raised decks, basements and storeys