Steel beams are used in commercial and residential construction projects. In recent years, the cost of steel has dropped to the point that it is often comparable in price to traditional wood beams. One benefit to steel beams is durability, as structural steel will last longer than wood. It is also impervious to insect infestation.

### Allowable spans

The formula for figuring the allowable span, or distance between, for steel beams takes into account a great many factors. Some of the items included in these calculations are the number of floors in the structure, the type of sub-flooring the columns used to support the beams rest on and the load limit of the beam.

### Steel beam standards

The standards for structural steel beams were developed by the American Iron and Steel Institute. A floor live load weight of approximately 18kg. per square foot on the first supported level and 13.6kg. per square foot on any additional levels is used to determine allowable spans. This guideline is intended for designers and architects to use when designing a structure.

### Calculating weight limits

When calculating steel beam spans, the allowable load weight must also include the weight of the beams and any columns. Additionally, the load weights of upper floors must also include load-bearing walls. Roofing is generally not considered in these calculations.