Easy Wood Calc

How many balusters for an 8 ft railing section?

Short answer

An 8 ft railing section (92½ inches between 4×4 posts) takes 17 balusters of 1½ inch stock with an even gap of 3.72 inches — a hair under 3-3/4 in on a tape — and 5-1/4 inches on center.

How to work it out

  1. (92-1/2 in − 3-3/4 in) ÷ (1-1/2 in + 3-3/4 in) = 16.9 → round up to 17 balusters
  2. (92-1/2 in − 17 × 1-1/2 in) ÷ 18 gaps = a hair under 3-3/4 in (3.72 in)

Here the exact gap, 3.72 in, falls between the marks on a tape. Round it up to 3¾ in and eighteen gaps grow by half an inch, leaving a short last gap; round it down to 3-11/16 in and the extra lands in the end gaps, which can creep to 4 in. Rip the spacer a hair under 3¾ in and dry-fit the section before you fasten.

Eight-foot posts also mean longer rails, which flex more between posts. Many railing systems and codes limit the rail span — check the manufacturer’s instructions and your local code before you settle on 8 ft.

Adjust for your project

On a stair, pick the stair option and measure along the sloped rail.
in
Level: 6 ft centers with 4×4 posts = 68½ in. Stair: measure along the rail, post face to post face.
in
2×2 = 1½ in; round metal ≈ ¾ in
in
US: keep deck gaps under 4 in; on the open side of a stair the IRC allows up to 4-3/8 in. UK: under 100 mm.
More options: Layout
An odd count puts a baluster in the middle, an even count a gap. Matching every section looks tidier.
Balusters per section17 balusters
Gap (cut your spacer to this)a hair under 3-3/4 in
Exact gap (decimal)
3.72 in
Middle of the section
A baluster, centered
Balusters for all sections
17 balusters
Center-to-center spacing
5-1/4 in
Post face to first baluster center
4-1/2 in
Screws (2 top, 2 bottom each)
68 screws
  • Balusters and 2×2s are not perfectly uniform. Measure a few, and cut a spacer block to the exact gap instead of measuring each one.
Check your codeCode limits vary by jurisdiction — confirm with your building department before you cut or build. (IRC R312)

For this job · affiliate link
Cordless drill/driver kit68 screws, each within an inch of a baluster end — pre-drill every one or the 2×2s split. A drill and a driver (or two batteries) makes it one pass.
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Balusters for an 8 ft section, by largest gap allowed

Balusters for an 8 ft section, by largest gap allowed
Largest gap allowedBalusters per sectionExact gap (decimal)Center-to-center spacing
3 in20 balusters2.98 in4-1/2 in
3.25 in19 balusters3.2 in4-11/16 in
3.5 in18 balusters3.45 in4-15/16 in
3.75 in17 balusters3.72 in5-1/4 in

What to know about an 8 ft railing section

Eighteen gaps of 3.72 in stay under the 4 in sphere limit in IRC R312.1.3 with only about ¼ in to spare — roughly half the margin of the 6 ft layout. Buy straight, dry balusters for these sections. A post that leans in or out changes the section length by more than that margin, so measure between the posts at the top rail and at the bottom rail and use the larger figure.

If your plans or inspector ask for a 3½ in design gap, set the maximum to 3½ in: the section then takes 18 balusters with gaps a hair over 3-7/16 in. One more baluster per section is a small price for a railing that will still pass after a summer of drying.

Four 8 ft sections — 32 ft of railing, such as both 16 ft sides of a freestanding 12×16 deck — take 68 balusters and 272 screws. Fewer posts is the appeal of 8 ft spacing; the rail span is the cost, so size the rails to the railing maker’s or your plans’ limits.

The tidier layout is How many balusters for a 6 ft railing section, where the gap comes out to exactly 3½ in. For the steps that usually meet the railing, see How many steps for a 3 ft deck.

Different size? Use the full Baluster Spacing Calculator.

What you’ll need

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Frequently asked questions

How many balusters for four 8 ft railing sections?

68 balusters — 17 balusters per section — and 272 screws at two per end.

How many balusters for an 8 ft section with a 3½ in maximum gap?

18 balusters, with gaps a hair over 3-7/16 in (3.45 in) and 4-15/16 in on center.

Other common sizes

Sources