Deck Railing Calculator
Railing posts, balusters and rail length.
Enter your values
Enter the railing perimeter in ft.
Enter the post spacing in ft.
Enter the baluster width in in.
Enter the max gap allowed in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Posts needed
- 11
- Rail sections
- 10
- Balusters per section
- 14
- Total balusters
- 140
Quick answer
Railing posts are spaced along the perimeter and balusters are spaced to meet the code maximum gap, usually 4 inches.
balusters per section = ceil((post spacing - baluster width)/(gap+width))
At a glance
| What it does | Railing posts, balusters and rail length. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Railing perimeter, Post spacing, Baluster width, Max gap allowed |
| Main output | Posts needed |
| Formula | balusters per section = ceil((post spacing - baluster width)/(gap+width)) |
| Cost | Free — no sign-up, no download |
How to use the Deck Railing Calculator
- 1Measure the total railing perimeter and choose a post spacing (commonly 6 ft max).
- 2Enter baluster width and the maximum code gap, usually 4 inches so a sphere cannot pass.
- 3The calculator spaces balusters evenly within each section to meet the gap limit.
Inputs explained
- Railing perimeter(ft)
- Enter the railing perimeter in ft.
- Post spacing(ft)
- Enter the post spacing in ft.
- Baluster width(in)
- Enter the baluster width in in.
- Max gap allowed(in)
- Enter the max gap allowed in in.
Worked example
Using the values the calculator loads with:
Inputs
- Railing perimeter60 ft
- Post spacing6 ft
- Baluster width1.5 in
- Max gap allowed4 in
Results
- Posts needed11
- Rail sections10
- Balusters per section14
- Total balusters140
Frequently asked questions
What is the standard baluster gap rule?
Most codes require gaps small enough that a 4-inch sphere cannot pass through.
Do corner posts count twice?
Enter true perimeter length; the calculator already adds one extra post for the closing corner.
What do I need to enter into the Deck Railing Calculator?
Just 4 values: railing perimeter, post spacing, baluster width, max gap allowed. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Deck Railing Calculator work out the answer?
Railing posts are spaced along the perimeter and balusters are spaced to meet the code maximum gap, usually 4 inches. It applies the formula balusters per section = ceil((post spacing - baluster width)/(gap+width)) and shows the working so you can check each step by hand.
Is the Deck Railing Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.