From a count to marks on the rail
- 01Count one opening first
- Balusters per opening describes the fitted layout. Total balusters also includes identical openings and any extras you deliberately entered; extras do not change the spacing.
- 02Use the right kind of spacing
- The equal clear gap is the empty space between faces. Centre-to-centre spacing includes one baluster width. A spacer block and a centre-mark template therefore use different numbers.
- 03Keep one measuring origin
- Use the cumulative edge or centre marks from the same inside post face. Check the far-end gap against the near-end gap rather than accumulating a rounded spacing with each step.
Compare an opening and a repeated order
1. Two 1.8 m openings plus spares
Complete inputs
Measurements
- Clear opening
- 1800 mm
- Baluster width
- 50 mm
- Maximum clear gap
- 100 mm
Project quantity
- Identical openings
- 2
- Extra balusters
- 2
Expected result
- Balusters per opening
- 12
- Total balusters
- 26
- Calculated clear gap (not rounded up)
- 92.307 mm
- Centre-to-centre
- 142.308 mm
- Extra balusters
- 2
Manual derivation
- N = ceil(1700 / 150) = 12 per opening.
- Two openings require 24 balusters; adding two spares gives 26.
2. Eight-foot clear opening
Complete inputs
Measurements
- Clear opening
- 8 ft
- Baluster width
- 1 1/2 in
- Maximum clear gap
- 4 in
Project quantity
- Identical openings
- 1
- Extra balusters
- 0
Expected result
- Balusters per opening
- 17
- Total balusters
- 17
- Calculated clear gap (not rounded up)
- 3.9166 in
- Centre-to-centre
- 5 7/16 in
- Extra balusters
- 0
Manual derivation
- N = ceil((96 in - 4 in) / (1.5 in + 4 in)) = 17 balusters.
- Seventeen balusters occupy 25.5 in; the remaining 70.5 in divides across 18 equal gaps, giving 3.9166 in clear and 5.4166 in centre to centre.
Example drawing
Fit-to-width summary
Opening 8 ft · centres 5 7/16 in. The gap display is never rounded above the calculated maximum. The complete keyboard-focusable diagram follows.
Cumulative markout from the left inside face
Measure every position from the same fixed datum. Do not step off a rounded gap or centre interval; repeated rounded intervals can accumulate error.
| Baluster | Left edge | Center mark | Right edge |
|---|---|---|---|
| 1 | 3 15/16 in | 4 11/16 in | 5 7/16 in |
| 2 | 9 5/16 in | 10 1/16 in | 10 13/16 in |
| 3 | 1 ft 2 3/4 in | 1 ft 3 1/2 in | 1 ft 4 1/4 in |
| 4 | 1 ft 8 3/16 in | 1 ft 8 15/16 in | 1 ft 9 11/16 in |
| 5 | 2 ft 1 9/16 in | 2 ft 2 5/16 in | 2 ft 3 1/16 in |
| 6 | 2 ft 7 in | 2 ft 7 3/4 in | 2 ft 8 1/2 in |
| 7 | 3 ft 7/16 in | 3 ft 1 3/16 in | 3 ft 1 15/16 in |
| 8 | 3 ft 5 13/16 in | 3 ft 6 9/16 in | 3 ft 7 5/16 in |
| 9 | 3 ft 11 1/4 in | 4 ft | 4 ft 3/4 in |
| 10 | 4 ft 4 11/16 in | 4 ft 5 7/16 in | 4 ft 6 3/16 in |
| 11 | 4 ft 10 1/16 in | 4 ft 10 13/16 in | 4 ft 11 9/16 in |
| 12 | 5 ft 3 1/2 in | 5 ft 4 1/4 in | 5 ft 5 in |
| 13 | 5 ft 8 15/16 in | 5 ft 9 11/16 in | 5 ft 10 7/16 in |
| 14 | 6 ft 2 5/16 in | 6 ft 3 1/16 in | 6 ft 3 13/16 in |
| 15 | 6 ft 7 3/4 in | 6 ft 8 1/2 in | 6 ft 9 1/4 in |
| 16 | 7 ft 1 3/16 in | 7 ft 1 15/16 in | 7 ft 2 11/16 in |
| 17 | 7 ft 6 9/16 in | 7 ft 7 5/16 in | 7 ft 8 1/16 in |
Before transferring the marks
- Measuring to post centres instead of the clear inside opening.
- Treating a common gap preset as a local code approval.
- Rounding an equal gap up after calculation.
Clear gaps and actual widths
- Does the spacing include both end gaps?
- Yes. A layout with N balusters has N + 1 equal clear gaps, including one at each inside post face.
- Can this calculate stair balusters?
- No. This calculator handles a level clear opening. Stair angle, tread and riser geometry, handrail transitions, and product-specific stair rules need a separate layout.
- Why must I enter the actual baluster width?
- Nominal product names may not equal the installed width. The count and centre marks use the physical width you enter.
MaterialNest last reconciled this level-opening layout on September 13, 2026; the published count and marks are separate from a project-specific guard review. Editorial and correction policy.
Auditable calculation record
The equal-gap calculation record
These equal-gap marks are a planning layout for the clear opening and baluster width you entered. Confirm the permitted opening, selected product, guard details, and local requirements before building; the marks do not certify a compliant or safe guard. Ask a qualified professional to review critical railing work.
- Formula version
- 1.1.0
- Last reconciled
- September 13, 2026
- Measurement datum
- Measure the finished clear opening between the two inside post faces.
- Rounding
- The baluster count rounds up to a whole item. The equal gap keeps full precision and is never displayed above the calculated maximum.
- Known exclusions
- Level openings only; stair geometry, guard design, connections, and the permitted project gap are not selected.