Baluster Calculator
Find how many balusters a railing needs so no gap exceeds 4 in, and lay them out evenly with the spacing and center marks.
Change the values and press Calculate to work out your own figures.
Balusters for a railing
Enter the railing's length, the posts and the baluster size and largest gap.
Show the working
- section = (railing − posts × post width) ÷ (posts − 1)
- per section = ⌈(section − gap) ÷ (baluster + gap)⌉
Spacing for one section
Enter the section's length between posts, the baluster width and the largest gap.
| Baluster | Center | Decimal |
|---|---|---|
| 1 | 4 3/8″ | 4.364 in |
| 2 | 9 1/2″ | 9.477 in |
| 3 | 1′ 2 9/16″ | 14.591 in |
| 4 | 1′ 7 11/16″ | 19.705 in |
| 5 | 2′ 13/16″ | 24.818 in |
| 6 | 2′ 5 15/16″ | 29.932 in |
| 7 | 2′ 11 1/16″ | 35.045 in |
| 8 | 3′ 4 3/16″ | 40.159 in |
| 9 | 3′ 9 1/4″ | 45.273 in |
| 10 | 4′ 2 3/8″ | 50.386 in |
Show the working
- balusters = ⌈(section − gap) ÷ (baluster + gap)⌉
- even gap = (section − balusters × width) ÷ (balusters + 1)
How to use it
Enter the railing's length, the posts and the baluster size and largest gap. Enter the section's length between posts, the baluster width and the largest gap.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
balusters per section = ⌈(section − gap) ÷ (baluster + gap)⌉ even gap = (section − balusters × baluster) ÷ (balusters + 1)
Code
The IRC allows no opening a 4 in sphere can pass through; measure tapered balusters at their narrowest. Check your local code.
Questions
How many balusters for a 10 ft railing?
About 20 with 1.5 in balusters, 3 posts of 3.5 in and gaps of at most 4 in.
How many balusters per foot?
About 2.2 at 1.5 in wide and 4 in apart.
Formulas
balusters per section = ⌈(section − gap) ÷ (baluster + gap)⌉ even gap = (section − balusters × baluster) ÷ (balusters + 1)
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.