A 4 ft (48") deck railing between posts takes 9 wood balusters (1-1/2") at 3-7/16" gaps or 10 metal balusters (3/4") at 3-11/16", both under the IRC 4" sphere. Hook the tape on the post once: the first wood edge goes at 3-7/16", the next at 8-3/8", then every 4-15/16".
48" 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 | 3-7/16" | 4-3/16" | 3.450" | |
| 2 | Leading edge | 8-3/8"+ | 9-1/8"+ | 8.400" | |
| 3 | Leading edge | 13-3/8"− | 14-1/8"− | 13.350" | |
| 4 | Leading edge | 18-5/16" | 19-1/16" | 18.300" | |
| 5 | Leading edge | 23-1/4" | 24" | 23.250" | |
| 6 | Leading edge | 28-3/16" | 28-15/16" | 28.200" | |
| 7 | Leading edge | 33-1/8"+ | 33-7/8"+ | 33.150" | |
| 8 | Leading edge | 38-1/8"− | 38-7/8"− | 38.100" | |
| 9 | Leading edge | 43-1/16" | 43-13/16" | 43.050" |
4x4 posts at 51-1/2" on centre: inside the 6'-0" AWC DCA 6 guard-post limit.
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| 9 | 3-7/16" | 4-15/16" | 3-7/16" | 10 | ||
| 10 | 3-11/16" | 4-7/16" | 3-11/16" | 11 | ||
| 10 | 3-7/16"+ | 4-7/16" | 3-7/16" | 11 | ||
| 7 | 2-15/16" | 6-7/16" | 2-15/16" | 8 |
| 1 | 3-7/16" | 4-3/16" | 3.450" |
|---|---|---|---|
| 2 | 8-3/8"+ | 9-1/8"+ | 8.400" |
| 3 | 13-3/8"− | 14-1/8"− | 13.350" |
| 4 | 18-5/16" | 19-1/16" | 18.300" |
| 5 | 23-1/4" | 24" | 23.250" |
| 6 | 28-3/16" | 28-15/16" | 28.200" |
| 7 | 33-1/8"+ | 33-7/8"+ | 33.150" |
| 8 | 38-1/8"− | 38-7/8"− | 38.100" |
| 9 | 43-1/16" | 43-13/16" | 43.050" |
Every baluster is 4-15/16" on centre after the first.
| 1 | 3-11/16" | 4-1/16" | 3.682" |
|---|---|---|---|
| 2 | 8-1/8" | 8-1/2" | 8.114" |
| 3 | 12-9/16"− | 12-15/16"− | 12.545" |
| 4 | 17"− | 17-3/8"− | 16.977" |
| 5 | 21-7/16"− | 21-13/16"− | 21.409" |
| 6 | 25-13/16"+ | 26-3/16"+ | 25.841" |
| 7 | 30-1/4"+ | 30-5/8"+ | 30.273" |
| 8 | 34-11/16"+ | 35-1/16"+ | 34.705" |
| 9 | 39-1/8" | 39-1/2" | 39.136" |
| 10 | 43-9/16" | 43-15/16" | 43.568" |
Every baluster is 4-7/16" on centre after the first.
05 / Field guide
This sheet lays out a 4 ft (48") 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.
48" ÷ (1-1/2" + gap) fits 9 balusters with 10 equal gaps of 3-7/16" (3.450"), 4-15/16" on centre.
From the post face the leading edges fall at 3-7/16", 8-3/8", 13-3/8", 18-5/16" and on in 4-15/16" steps. Buy 10 to allow 10% for splits and miscuts.
Thinner balusters need more of them: 10 at 3-11/16" gaps, 4-7/16" on centre. The first four marks: 3-11/16", 8-1/8", 12-9/16", 17".
1" metal or composite takes 10 at 3-7/16"; 3-1/2" flat pickets take 7 at 2-15/16".
With 4x4 posts the centres are 51-1/2" 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
9 of 1-1/2" wood or 10 of 3/4" metal for 48" between posts, centred with equal gaps. Buy about 10% more.
3-7/16" clear between 1-1/2" balusters (4-15/16" on centre) or 3-11/16" between 3/4" balusters (4-7/16" on centre).
Its leading edge sits one gap from the post face: 3-7/16" for 1-1/2" wood or 3-11/16" for 3/4" metal.
No. On 4x4 posts the centres are 51-1/2" apart, within the 6'-0" AWC DCA 6 limit.
10 at 3-7/16" gaps; 3-1/2" flat pickets take 7 at 2-15/16".
Raised decks, basements and storeys