Railing Calculator
Work out a railing's quantities — from its length and your spacings — in balusters, posts and total length.
A railing is gaps plus one — balusters and posts both count that way. This calculator is that count, from your length and spacings.
Enter the length; the quantities follow.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the railing length.
- Enter the baluster spacing and the post spacing.
- Read the balusters, the posts and the total length.
Worked example
| Railing | 5 m long |
|---|---|
| Baluster spacing | 100 mm |
| Balusters | ceil(5,000 ÷ 100) + 1 = 51 |
| Post spacing | 1.5 m |
| Posts | ceil(5 ÷ 1.5) + 1 = 5 |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
Why 100 mm baluster spacing?
Because many codes require that a 100 mm sphere cannot pass through the balusters — a child-safety rule. 100 mm is the common maximum gap; check your local code.
Why add 1 to the balusters and posts?
Because the count is the gaps plus one: a 5 m railing at 100 mm spacing has 50 gaps and 51 balusters — one at each end and one between every gap.
How far apart should railing posts be?
About 1.5 m is a common planning figure for a sturdy rail. Longer spans need a stiffer rail. Verify the spacing against local code.
Is this a substitute for building design?
No. This is a quantity calculation for planning. Railing dimensions, structural requirements and building-code compliance vary by location — see the safety notice.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.