# Steel beam span rule of thumb: RSJ, i-beam, W-beam, or UB

A common rule of thumb for steel beam spans is typically about “20 times the depth of the beam” guideline. This means the span (in feet) should be on an average 20 times the depth (in inches) of the steel beam such as depth (in inches) = (span (in feet)×12)/20.

However, the size of steel beam you need for a specific span depends on various factors such as the load it will bear, design, locality, types of structure, building codes and regulation, and structural requirements.

In steel structure steel beam is also called Rolled steel joist (RSJ). It is actually a long beam made from hot or cold-rolled steel. This is also known as a Universal Beam (i-Beam), hot rolled Steel section such as H beam (universal column), W-beam, I beam (universal beam), angles, channels and etc.

## Steel beam span rule of thumb: RSJ, i-beam, W-beam, or UB

As per steel beam span rule of thumb, the depth of steel beam are in the range of 1/2 inches of depth for each foot of span (L/24). Or depth of the steel beam as roof joist = 0.5 × span, where length expressed in meters and depth members in mm. For example, if steel beam span is 24 feet, then their depth = (24 × 12) ÷ 24 = 12 inches, and their width is 1/2 to 1/3 of the depth.

Steel beam span rule of thumb for steel design are following:-

1. Span to depth ratio (L/ds) for steel beam should be range from 20 to 28.
2. Span to depth ratio (L/ds) for steel floor member (floor joists) is 20, or depth of the floor joist (in inches) = 0.6 × span length (in feet)
3. L/ds for steel roof member (roof joists) is 25, or depth of the roof joist (in inches) = 0.5 × span length (in feet)
4. L/ds for composite beam is 22, or depth of the composite beams (in inches) = 0.55 × span length (in feet)
5. Span to depth ratio (L/ds) for steel plate girder should be 15, 12 for joist girder, 12 for steel truss and from 12 to 20 for space frame.

### Steel beam depth to span ratio

The depth-to-span ratio for steel beams depends on various factors such as the type of beam, loading conditions, and design codes. Typically, it ranges from L/20 to L/28 for common steel beams in building structures.

Typically Steel beam depth to span ratio (L/ds) is ranges from 1/20 to 1/28 for common steel beams, 1/24 for roof joists, 1/20 for floor joists, 1/22 for composite beam, 1/15 for steel plate girder, 1/12 for joist girder, 1/12 for steel truss and from 1/12 to 1/20 for space frame.

Conclusions:-
A common rule of thumb for steel beam spans, the depth of steel beam are in the range of 1/2 inches of depth for each foot of span (L/24) and and their width is 1/2 to 1/3 of the depth is often suitable for standard residential applications.