An 8 ft (96") deck railing between posts takes 18 wood balusters (1-1/2") at 3-5/8" gaps or 21 metal balusters (3/4") at 3-5/8", both under the IRC 4" sphere. Hook the tape on the post once: the first wood edge goes at 3-5/8", the next at 8-3/4", then every 5-1/8".
96" 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 | 3-5/8" | 4-3/8" | 3.632" | |
| 2 | Leading edge | 8-3/4" | 9-1/2" | 8.763" | |
| 3 | Leading edge | 13-7/8"+ | 14-5/8"+ | 13.895" | |
| 4 | Leading edge | 19"+ | 19-3/4"+ | 19.026" | |
| 5 | Leading edge | 24-3/16"− | 24-15/16"− | 24.158" | |
| 6 | Leading edge | 29-5/16"− | 30-1/16"− | 29.289" | |
| 7 | Leading edge | 34-7/16"− | 35-3/16"− | 34.421" | |
| 8 | Leading edge | 39-9/16" | 40-5/16" | 39.553" | |
| 9 | Leading edge | 44-11/16" | 45-7/16" | 44.684" | |
| 10 | Leading edge | 49-13/16" | 50-9/16" | 49.816" | |
| 11 | Leading edge | 54-15/16" | 55-11/16" | 54.947" | |
| 12 | Leading edge | 60-1/16"+ | 60-13/16"+ | 60.079" | |
| 13 | Leading edge | 65-3/16"+ | 65-15/16"+ | 65.211" | |
| 14 | Leading edge | 70-5/16"+ | 71-1/16"+ | 70.342" | |
| 15 | Leading edge | 75-1/2"− | 76-1/4"− | 75.474" | |
| 16 | Leading edge | 80-5/8"− | 81-3/8"− | 80.605" | |
| 17 | Leading edge | 85-3/4" | 86-1/2" | 85.737" | |
| 18 | Leading edge | 90-7/8" | 91-5/8" | 90.868" |
4x4 posts at 99-1/2" 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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| 18 | 3-5/8" | 5-1/8" | 3-5/8" | 20 | ||
| 21 | 3-5/8"+ | 4-3/8" | 3-5/8" | 24 | ||
| 20 | 3-5/8" | 4-5/8" | 3-5/8" | 22 | ||
| 13 | 3-5/8"− | 7-1/8" | 3-5/8" | 15 |
| 1 | 3-5/8" | 4-3/8" | 3.632" |
|---|---|---|---|
| 2 | 8-3/4" | 9-1/2" | 8.763" |
| 3 | 13-7/8"+ | 14-5/8"+ | 13.895" |
| 4 | 19"+ | 19-3/4"+ | 19.026" |
| 5 | 24-3/16"− | 24-15/16"− | 24.158" |
| 6 | 29-5/16"− | 30-1/16"− | 29.289" |
| 7 | 34-7/16"− | 35-3/16"− | 34.421" |
| 8 | 39-9/16" | 40-5/16" | 39.553" |
| 9 | 44-11/16" | 45-7/16" | 44.684" |
| 10 | 49-13/16" | 50-9/16" | 49.816" |
| 11 | 54-15/16" | 55-11/16" | 54.947" |
| 12 | 60-1/16"+ | 60-13/16"+ | 60.079" |
| 13 | 65-3/16"+ | 65-15/16"+ | 65.211" |
| 14 | 70-5/16"+ | 71-1/16"+ | 70.342" |
| 15 | 75-1/2"− | 76-1/4"− | 75.474" |
| 16 | 80-5/8"− | 81-3/8"− | 80.605" |
| 17 | 85-3/4" | 86-1/2" | 85.737" |
| 18 | 90-7/8" | 91-5/8" | 90.868" |
Every baluster is 5-1/8" on centre after the first.
| 1 | 3-5/8"+ | 4"+ | 3.648" |
|---|---|---|---|
| 2 | 8-1/16"− | 8-7/16"− | 8.045" |
| 3 | 12-7/16" | 12-13/16" | 12.443" |
| 4 | 16-13/16"+ | 17-3/16"+ | 16.841" |
| 5 | 21-1/4" | 21-5/8" | 21.239" |
| 6 | 25-5/8" | 26" | 25.636" |
| 7 | 30-1/16"− | 30-7/16"− | 30.034" |
| 8 | 34-7/16" | 34-13/16" | 34.432" |
| 9 | 38-13/16"+ | 39-3/16"+ | 38.830" |
| 10 | 43-1/4"− | 43-5/8"− | 43.227" |
| 11 | 47-5/8" | 48" | 47.625" |
| 12 | 52"+ | 52-3/8"+ | 52.023" |
| 13 | 56-7/16"− | 56-13/16"− | 56.420" |
| 14 | 60-13/16" | 61-3/16" | 60.818" |
| 15 | 65-3/16"+ | 65-9/16"+ | 65.216" |
| 16 | 69-5/8" | 70" | 69.614" |
| 17 | 74" | 74-3/8" | 74.011" |
| 18 | 78-7/16"− | 78-13/16"− | 78.409" |
| 19 | 82-13/16" | 83-3/16" | 82.807" |
| 20 | 87-3/16"+ | 87-9/16"+ | 87.205" |
| 21 | 91-5/8"− | 92"− | 91.602" |
Every baluster is 4-3/8" on centre after the first.
05 / Field guide
This sheet lays out an 8 ft (96") 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.
96" ÷ (1-1/2" + gap) fits 18 balusters with 19 equal gaps of 3-5/8" (3.632"), 5-1/8" on centre.
From the post face the leading edges fall at 3-5/8", 8-3/4", 13-7/8", 19" and on in 5-1/8" steps. Buy 20 to allow 10% for splits and miscuts.
Thinner balusters need more of them: 21 at 3-5/8"+ gaps, 4-3/8" on centre. The first four marks: 3-5/8", 8-1/16", 12-7/16", 16-13/16".
1" metal or composite takes 20 at 3-5/8"; 3-1/2" flat pickets take 13 at 3-5/8".
With 4x4 posts the centres would be 8' 3-1/2" apart, past the 6'-0" DCA 6 limit for prescriptive guard posts. Add 1 intermediate post (2 bays of about 46-1/4" 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
18 of 1-1/2" wood or 21 of 3/4" metal for 96" between posts, centred with equal gaps. Buy about 10% more.
3-5/8" clear between 1-1/2" balusters (5-1/8" on centre) or 3-5/8" between 3/4" balusters (4-3/8" on centre).
Its leading edge sits one gap from the post face: 3-5/8" for 1-1/2" wood or 3-5/8" for 3/4" metal.
Under AWC DCA 6, yes: guard posts may be at most 6'-0" apart, and 96" clear on 4x4 posts is 8' 3-1/2" on centre. Railing kits rated for longer sections are the exception.
20 at 3-5/8" gaps; 3-1/2" flat pickets take 13 at 3-5/8".
Raised decks, basements and storeys