A 4 ft (48" level) stair railing on a 7-1/2" × 10" stair takes 9 wood balusters at 3-7/16" gaps or 10 metal at 3-11/16", under the 4-3/8" stair sphere. Along the 36.9° rail every mark is the level one × 1.250: wood balusters sit 6-3/16" apart on the rail.
48" between posts (level)
Hook the tape on the post face at the top of the bottom rail and mark down the slope. Marks along the rail are the level positions × 1.2500 (1 ÷ cos 36.9°).
| Done | # | Mark | Along rail | Centre (rail) | Level |
|---|---|---|---|---|---|
| 1 | Leading edge | 4-5/16" | 5-1/4" | 3-7/16" | |
| 2 | Leading edge | 10-1/2" | 11-7/16" | 8-3/8"+ | |
| 3 | Leading edge | 16-11/16" | 17-5/8" | 13-3/8"− | |
| 4 | Leading edge | 22-7/8" | 23-13/16" | 18-5/16" | |
| 5 | Leading edge | 29-1/16" | 30" | 23-1/4" | |
| 6 | Leading edge | 35-1/4" | 36-3/16" | 28-3/16" | |
| 7 | Leading edge | 41-7/16" | 42-3/8" | 33-1/8"+ | |
| 8 | Leading edge | 47-5/8" | 48-9/16" | 38-1/8"− | |
| 9 | Leading edge | 53-13/16" | 54-3/4" | 43-1/16" |
Fillets: cut each one to the gap along the rail with the rake angle on both ends.
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" · 6-3/16" | 4-5/16" | 10 | ||
| 10 | 3-11/16" | 4-7/16" · 5-9/16" | 4-5/8" | 11 | ||
| 10 | 3-7/16"+ | 4-7/16" · 5-9/16" | 4-5/16" | 11 | ||
| 7 | 2-15/16" | 6-7/16" · 8-1/16" | 3-11/16" | 8 |
| 1 | 3-7/16" | 4-3/16" | 4-5/16" | 4.313" |
|---|---|---|---|---|
| 2 | 8-3/8"+ | 9-1/8"+ | 10-1/2" | 10.500" |
| 3 | 13-3/8"− | 14-1/8"− | 16-11/16" | 16.688" |
| 4 | 18-5/16" | 19-1/16" | 22-7/8" | 22.875" |
| 5 | 23-1/4" | 24" | 29-1/16" | 29.063" |
| 6 | 28-3/16" | 28-15/16" | 35-1/4" | 35.250" |
| 7 | 33-1/8"+ | 33-7/8"+ | 41-7/16" | 41.438" |
| 8 | 38-1/8"− | 38-7/8"− | 47-5/8" | 47.625" |
| 9 | 43-1/16" | 43-13/16" | 53-13/16" | 53.813" |
Along-rail marks are the level distance ÷ cos 36.9° (× 1.2500).
| 1 | 3-11/16" | 4-1/16" | 4-5/8"− | 4.602" |
|---|---|---|---|---|
| 2 | 8-1/8" | 8-1/2" | 10-1/8"+ | 10.142" |
| 3 | 12-9/16"− | 12-15/16"− | 15-11/16" | 15.682" |
| 4 | 17"− | 17-3/8"− | 21-1/4"− | 21.222" |
| 5 | 21-7/16"− | 21-13/16"− | 26-3/4" | 26.761" |
| 6 | 25-13/16"+ | 26-3/16"+ | 32-5/16" | 32.301" |
| 7 | 30-1/4"+ | 30-5/8"+ | 37-13/16"+ | 37.841" |
| 8 | 34-11/16"+ | 35-1/16"+ | 43-3/8" | 43.381" |
| 9 | 39-1/8" | 39-1/2" | 48-15/16"− | 48.920" |
| 10 | 43-9/16" | 43-15/16" | 54-7/16"+ | 54.460" |
Along-rail marks are the level distance ÷ cos 36.9° (× 1.2500).
05 / Field guide
This sheet lays out a 4 ft (48") stair railing between post faces, measured level along a 7-1/2" × 10" stair. It compares 1-1/2" wood with 3/4" metal, gives every mark from one hook of the tape, and checks the 4-3/8" 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 level and 6-3/16" along the rail.
From the post face the leading edges fall at 4-5/16", 10-1/2", 16-11/16", 22-7/8" and on in 6-3/16" 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 (5-9/16" along the rail). The first four marks: 4-5/8", 10-1/8", 15-11/16", 21-1/4".
1" metal or composite takes 10 at 3-7/16"; 3-1/2" flat pickets take 7 at 2-15/16".
On a 7-1/2" rise and 10" run the rail climbs 36" over this 48" run and measures 60" along its length. Clear gaps are measured level, square to the plumb balusters; every tape mark along the rail is the level distance ÷ cos 36.9° = × 1.2500.
Cut fillet strips to 4-5/16" for wood or 4-5/8" for metal, with 36.9° on both ends. Keep the bottom rail within 1-1/2" of the nosing line so the tread-riser triangle stays under a 6" sphere.
With 4x4 posts the centres are 51-1/2" apart, inside the 6'-0" DCA 6 limit for guard posts.
The rail sits 34" above the nosings (34" to 38" where it is also the handrail).
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), measured level; along the sloped rail the centres are 6-3/16" and 5-9/16".
Its leading edge sits one gap from the post face: 4-5/16" for 1-1/2" wood or 4-5/8" for 3/4" metal, measured along the rail.
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