A 6 ft (72") deck railing between posts takes 13 wood balusters (1-1/2") at 3-3/4" gaps or 16 metal balusters (3/4") at 3-1/2", both under the IRC 4" sphere. Hook the tape on the post once: the first wood edge goes at 3-3/4", the next at 9", then every 5-1/4".
72" 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 | 3-3/4" | 4-1/2" | 3.750" | |
| 2 | Leading edge | 9" | 9-3/4" | 9.000" | |
| 3 | Leading edge | 14-1/4" | 15" | 14.250" | |
| 4 | Leading edge | 19-1/2" | 20-1/4" | 19.500" | |
| 5 | Leading edge | 24-3/4" | 25-1/2" | 24.750" | |
| 6 | Leading edge | 30" | 30-3/4" | 30.000" | |
| 7 | Leading edge | 35-1/4" | 36" | 35.250" | |
| 8 | Leading edge | 40-1/2" | 41-1/4" | 40.500" | |
| 9 | Leading edge | 45-3/4" | 46-1/2" | 45.750" | |
| 10 | Leading edge | 51" | 51-3/4" | 51.000" | |
| 11 | Leading edge | 56-1/4" | 57" | 56.250" | |
| 12 | Leading edge | 61-1/2" | 62-1/4" | 61.500" | |
| 13 | Leading edge | 66-3/4" | 67-1/2" | 66.750" |
4x4 posts at 75-1/2" on centre exceed the 6'-0" AWC DCA 6 guard-post limit: add a middle post or use a railing kit rated for this length.
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| 13 | 3-3/4" | 5-1/4" | 3-3/4" | 15 | ||
| 16 | 3-1/2"+ | 4-1/4" | 3-1/2" | 18 | ||
| 15 | 3-9/16" | 4-9/16" | 3-9/16" | 17 | ||
| 10 | 3-3/8" | 6-7/8" | 3-3/8" | 11 |
| 1 | 3-3/4" | 4-1/2" | 3.750" |
|---|---|---|---|
| 2 | 9" | 9-3/4" | 9.000" |
| 3 | 14-1/4" | 15" | 14.250" |
| 4 | 19-1/2" | 20-1/4" | 19.500" |
| 5 | 24-3/4" | 25-1/2" | 24.750" |
| 6 | 30" | 30-3/4" | 30.000" |
| 7 | 35-1/4" | 36" | 35.250" |
| 8 | 40-1/2" | 41-1/4" | 40.500" |
| 9 | 45-3/4" | 46-1/2" | 45.750" |
| 10 | 51" | 51-3/4" | 51.000" |
| 11 | 56-1/4" | 57" | 56.250" |
| 12 | 61-1/2" | 62-1/4" | 61.500" |
| 13 | 66-3/4" | 67-1/2" | 66.750" |
Every baluster is 5-1/4" on centre after the first.
| 1 | 3-1/2"+ | 3-7/8"+ | 3.529" |
|---|---|---|---|
| 2 | 7-13/16" | 8-3/16" | 7.809" |
| 3 | 12-1/16"+ | 12-7/16"+ | 12.088" |
| 4 | 16-3/8" | 16-3/4" | 16.368" |
| 5 | 20-5/8"+ | 21"+ | 20.647" |
| 6 | 24-15/16" | 25-5/16" | 24.926" |
| 7 | 29-3/16"+ | 29-9/16"+ | 29.206" |
| 8 | 33-1/2" | 33-7/8" | 33.485" |
| 9 | 37-3/4" | 38-1/8" | 37.765" |
| 10 | 42-1/16"− | 42-7/16"− | 42.044" |
| 11 | 46-5/16" | 46-11/16" | 46.324" |
| 12 | 50-5/8"− | 51"− | 50.603" |
| 13 | 54-7/8" | 55-1/4" | 54.882" |
| 14 | 59-3/16"− | 59-9/16"− | 59.162" |
| 15 | 63-7/16" | 63-13/16" | 63.441" |
| 16 | 67-3/4"− | 68-1/8"− | 67.721" |
Every baluster is 4-1/4" on centre after the first.
05 / Field guide
This sheet lays out a 6 ft (72") 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.
72" ÷ (1-1/2" + gap) fits 13 balusters with 14 equal gaps of 3-3/4" (3.750"), 5-1/4" on centre.
From the post face the leading edges fall at 3-3/4", 9", 14-1/4", 19-1/2" and on in 5-1/4" steps. Buy 15 to allow 10% for splits and miscuts.
Thinner balusters need more of them: 16 at 3-1/2"+ gaps, 4-1/4" on centre. The first four marks: 3-1/2", 7-13/16", 12-1/16", 16-3/8".
1" metal or composite takes 15 at 3-9/16"; 3-1/2" flat pickets take 10 at 3-3/8".
With 4x4 posts the centres would be 6' 3-1/2" apart, past the 6'-0" DCA 6 limit for prescriptive guard posts. Add 0 intermediate post (1 bays of about 72" clear), or use a railing kit rated for this section length.
The guard top sits at least 36" above the deck and the bottom rail less than 4" above it.
Questions
13 of 1-1/2" wood or 16 of 3/4" metal for 72" between posts, centred with equal gaps. Buy about 10% more.
3-3/4" clear between 1-1/2" balusters (5-1/4" on centre) or 3-1/2" between 3/4" balusters (4-1/4" on centre).
Its leading edge sits one gap from the post face: 3-3/4" for 1-1/2" wood or 3-1/2" for 3/4" metal.
Under AWC DCA 6, yes: guard posts may be at most 6'-0" apart, and 72" clear on 4x4 posts is 6' 3-1/2" on centre. Railing kits rated for longer sections are the exception.
15 at 3-9/16" gaps; 3-1/2" flat pickets take 10 at 3-3/8".
Raised decks, basements and storeys