Steel railing dimensions come from two places: the Ontario Building Code, which sets heights, openings, graspability and loads, and the structural design, which sets the size of the posts, rails and anchors that meet those loads. For a typical steel railing, that means a round handrail of about 30 mm to 50 mm diameter (NPS 1-1/4 or 1-1/2 pipe are common), pickets spaced so no gap passes a 100 mm sphere, guards at least 1,070 mm high in most locations (900 mm inside a house), and posts sized and spaced to carry the guard loads. Here is how each dimension is decided.
The code numbers that fix a railing's shape
Before any steel size is chosen, the code sets the envelope. These are the key numbers from Section 9.8. of the 2024 Ontario Building Code (Part 9 buildings). The full rules, with exceptions, are in Ontario Building Code guard and handrail rules for steel railings.
| Dimension | Requirement |
|---|---|
| Guard height, general | At least 1,070 mm |
| Guard height within a dwelling unit, and on exterior surfaces serving one house up to 1,800 mm above ground | At least 900 mm |
| Required handrail height | 865 mm to 1,070 mm, measured from a line through the tread nosings |
| Openings through a required guard | Must stop a 100 mm sphere |
| Triangle at tread, riser and bottom rail on stairs | Must stop a 150 mm sphere (not in industrial occupancies) |
| Non-climbable zone | No climbable member or opening between 140 mm and 900 mm above the walking surface (with exceptions) |
| Handrail clearance to wall | At least 50 mm, or 60 mm to a rough surface |
| Projection of handrails, supports and stringers into required stair width | No more than 100 mm |
Larger buildings fall under Part 3, which has similar but not identical rules. Your designer confirms which part applies.
Handrail size: pipe and tube diameters
The part of the railing you hold has to be graspable. Part 9 of the OBC requires handrails to be continually graspable along their length, and its explanatory note describes a profile that lets your fingers and thumb curl under the rail. Part 3 of the 2024 OBC is more specific: a circular handrail must have an outside diameter of 30 mm to 50 mm, and a non-circular one a perimeter of 100 mm to 160 mm with no cross-section dimension over 57 mm. Handrails on barrier-free ramps have a tighter range, 30 mm to 40 mm for round rails. Many designers use the Part 3 range as a practical guide for houses too.
Steel pipe is sized by nominal pipe size (NPS), which is not the actual diameter. Common handrail sizes:
| Nominal pipe size | Outside diameter | Schedule 40 wall | Fits 30 mm to 50 mm range? |
|---|---|---|---|
| NPS 1 | 33.4 mm (1.315 in) | 3.38 mm | Yes, but feels slim |
| NPS 1-1/4 | 42.2 mm (1.660 in) | 3.56 mm | Yes, the most common handrail size |
| NPS 1-1/2 | 48.3 mm (1.900 in) | 3.68 mm | Yes, near the top of the range |
| NPS 2 | 60.3 mm (2.375 in) | 3.91 mm | No, too large for a handrail; used for posts and bollards |
Round mechanical tube in sizes such as 38.1 mm (1-1/2 in) or 41.3 mm (1-5/8 in) outside diameter is also used, often with thinner walls than pipe. A flat bar cap on top of a guard is fine as a guard top rail, but a wide flat bar on its own usually isn't graspable, so a separate handrail is mounted on brackets where one is required. See steel stair railings and handrails for profile options.
Wall thickness and gauge
People often ask what gauge steel a railing should be. The trouble is that gauge numbers are not a single standard: sheet steel, tube and wire use different gauge tables, and the same number can mean slightly different thicknesses. As a rough guide, 11 gauge is about 3 mm, 14 gauge about 2 mm and 16 gauge about 1.5 mm.
For that reason, specify railing members by outside size and wall thickness in millimetres (for example, HSS 51 x 51 x 4.8, or 42.2 mm pipe with a 3.56 mm wall), not by gauge. It removes the guesswork when comparing quotes.
Practical points on wall thickness:
- Thin-wall tube (around 1.5 mm to 2 mm) is fine for pickets and decorative infill, but it is easy to burn through when welding and dents easily outdoors.
- About 3 mm and up is a common minimum for posts and top rails on residential guards, and makes welding and anchoring much more reliable.
- Heavier posts (HSS with walls of 4.8 mm, 6.4 mm or more) are common on commercial guards, cantilevered glass guards and exterior railings with long post spacing, as set by design.
Exterior tube also corrodes from the inside if water gets in, so cap open ends and seal or drain them, especially if the railing is galvanized and painted.
Pickets, posts and spacing
Pickets (balusters)
Square bar pickets of about 12.7 mm, 16 mm or 19 mm (1/2 in, 5/8 in or 3/4 in) and small square tube are the usual steel choices. The picket size isn't set by the code, but the gaps are. With 100 mm as the hard limit, pickets are normally laid out with a clear gap a little under that, often around 90 mm or less, so normal fabrication and installation variation can't push a gap over the limit. The code also checks that pickets can't be pushed apart: with a 0.1 kN load applied to adjacent members in opposite directions, the gap must still stop the 100 mm sphere. Slender flat bar pickets on long spans can fail this check even when the unloaded gap is fine.
Lay out pickets so the gaps are equal along each section, including at the posts. Measuring from finished surfaces matters here too: the gap under the bottom rail is checked to the finished floor or tread.
Posts
Steel railing posts are typically square HSS, square or rectangular bar, or pipe. Their size and spacing are linked: the guard has to resist the code loads at the top rail (including a horizontal line load or a point load, depending on location) plus loads on the infill. The 2024 OBC's handrail rules also call for handrails and supports to resist a 0.9 kN concentrated load in any direction.
Ontario publishes Supplementary Standard SB-7, "Guards for Housing and Small Buildings", with prescriptive guard designs. Its scope covers wood guards, so steel railings are normally sized by design: the fabricator's engineer or the project engineer checks the post, the base plate, the weld and the anchors. Post spacing then falls out of that check rather than a fixed rule.
Rails
Top and bottom rails are commonly flat bar, square tube or channel. The bottom rail is often set about 50 mm to 75 mm above the floor or treads, which keeps the gap below the 100 mm limit with room to spare. Avoid horizontal rails between 140 mm and 900 mm above the walking surface on required guards, because they can create a foothold.
Anchorage: the dimension that is easy to miss
Most railings that fail don't fail in the pickets. They fail at the base: a small base plate, light anchors, anchors too close to the edge of a slab, or a weld around a thin post. A few points to settle on the drawings:
- Mounting type: surface-mounted base plate, side (fascia) mounted to the stringer or slab edge, or cored into concrete
- Base plate size and thickness, and the anchor size, embedment and edge distance into concrete
- For wood decks and stairs, how the post connects to framing and blocking
Concrete edge distance matters a lot on balconies and stair edges, for the same reason it does on embed plates cast into concrete.
Getting a steel railing sized and quoted
We fabricate custom steel railings, stairs, gates and other miscellaneous steel in our shop, with CWB certified welding and shop drawings prepared in house. Engineering services are available for railings that need a stamped design. Send drawings, a sketch or site measurements, including run lengths, stair rise and run, finished floor heights and the mounting surface. We fabricate and deliver, and installation is by your installer or contractor.
Request a railing quote, or see our steel products for posts, plates and miscellaneous steel. For what drives the price, see steel railing cost per foot.
Frequently asked questions
What size pipe is used for a steel handrail?
Round handrails are commonly made from NPS 1-1/4 pipe (42.2 mm outside diameter) or NPS 1-1/2 pipe (48.3 mm), or from round tube of similar size. Both fall within the 30 mm to 50 mm diameter range the Ontario Building Code sets for circular handrails in Part 3 buildings.
What gauge steel is used for railings?
Gauge numbers mean different thicknesses in different systems, so railings are better specified by wall thickness in millimetres. Light residential tube is often around 11 to 14 gauge (roughly 3 mm to 2 mm wall), while posts on commercial guards are typically heavier, sized by design for the guard loads.
How far apart can railing pickets be in Ontario?
Openings through a required guard must stop a 100 mm sphere, so the clear gap between pickets has to be less than 100 mm. On stairs, the triangle formed by the tread, riser and bottom rail must stop a 150 mm sphere, except in industrial occupancies.
How far apart should steel railing posts be?
There is no single code number for steel post spacing. The guard has to resist the code loads, and the post size, base plate, weld and anchors set how far apart posts can be. Ontario's SB-7 guard designs are for wood guards, so steel railings are sized by design.
How high is a steel railing in Ontario?
Most guards must be at least 1,070 mm high, or 900 mm within a dwelling unit and on lower exterior surfaces serving a single house. Required handrails must be 865 mm to 1,070 mm high.
