How Far Can a Steel Beam Span Without Support?

Designing, renovating, or building open spaces within a structure can be a challenge with dimensional lumber. There are times when a steel beam may be a better choice to achieve the open space desired. If you’re wondering how far can a steel beam span without support, we’re here to help!

A steel beam span depends on its depth, weight, width, strengths, flange and web thicknesses, type, loads, and force variables, plus other factors. A W6x9 can span 14’-3” while supporting a tributary span of 6’ while a W8x18 can span 14’-0” while supporting one of 24’, depending on all variables. The longest continuous truss span presently, though, is 1,312 feet in the Ikitsuki Bridge.

In this guide, we’ll identify the type of steel beams used in residential construction, the rule of thumb for steel beam span, and how far it can span without support. We’ll discuss I-beam sizes, provide a residential steel beam span table, and recommend an I-beam span calculator. We’ll also include the maximum span and the cost of steel beams. Our aim is to provide you with the information you need for your building project.

How Far Can a Steel Beam Span Without Support

What Steel Beam Is Used in Residential Construction?

There are a number of different types of steel beams used in residential construction, all of which are manufactured to set standards. Some have specific purposes, and others are interchangeable and can be used for several purposes. There are H-beams, I-beams, L-section beams, T-section beams, W-beams, and Channel beams. The letter designation often, but not always, identifies the cross-sectional profile of the beam.

H-Beams are also known as wide-flange I-beams but are heavier and can span greater distances than most other beams. They are more commonly used in larger residential buildings. Able to carry upwards of 1,000 tons, they require greater foundational support. Originally used vertically to carry other steel members, they are now also used as beams. Due to their weight and size, they often require heavy equipment to place.

I-Beams or Universal Beams are commonly used in residential construction to increase spans or structural heights. Similar in profile to the H-Beam, it is lighter and has narrower, tapered flanges. I-beams are also sometimes referred to as Double-T or Rolled Steel Joists (RSJ).

L-section beams or angle beams have two legs of equal or unequal length forming a right angle. They have a high weight-to-strength ratio and have many uses in residential construction, including brick ledgers, headers, and for reinforcing other steel beams.

T-section beams are often used atop steel posts, pillars, or other beams and used for load bearing and to support or interlock with wood or steel beams. They can be riveted or bolted to link multiple sections of W- or I-beams together without the structural integrity being compromised.

W-Beams or Wide Flange I-Beams are comparably lightweight and smaller than other steel beams. They are used in residential construction and don’t require heavy supports as the I-beam does and won’t compromise wooden structural materials. It is easier and faster to place, can be bolted, riveted, and welded, and requires less space.

Channel beams have a ‘C’ or ‘U’ shaped cross-sectional profile forming a channel. Lightweight but strong, they are often used to bridge and carry lighter loads.

Steel Beam Span Rule of Thumb

The general rule of thumb to calculate the depth of a beam is to convert the span to inches and divide by 20. So, a 30-foot span is (30×12) 360 inches, divided by 20 (360÷20) is 18 inches deep. The beam’s width would be 1/3 to 1/2 its depth, so between 6” and 9” in this example. A beam can also cantilever or overhang a maximum of 3/8 of its supported span. For the 30-foot span, the overhang can’t be more than (30×3÷8) 11.25 feet.

How Far Can a Steel Beam Span Without Support?

Steel Beam Span Rule of Thumb

The size, metal thickness, and type of steel beam usually determine its unsupported span. It’s common practice for a Structural Engineer to identify beam sizes, placement, and supports based on the weight distribution of building components and loads. Since steel I-beams are commonly used in light residential construction, we’ll focus on them.

The span depends on the depth and weight of the I-beam, among other variables and factors. The greater the depth and weight, the further it can span. However, load distribution factors and steel thicknesses must be considered too. The Beam Span Rule of Thumb can be used to identify the distance a beam can span too.

If you happen to have a 10” deep I-beam laying around and want to know how far it could span, rewrite the Rule. Take the depth in inches and multiply by 20 (10”x20=200) and then divide by 12 (200÷12) to convert the span to feet (16.67). So, a 10” deep I-beam has a maximum span of 16.67 feet, depending on its weight and other factors.

What Sizes Do Steel I-Beams Come In?

I-beams are manufactured to meet U.S. standards or the national standards for where they are to be used. An I-beam has a top and bottom flange sandwiching a long, single vertically oriented center steel strip or web. The web of the I-beam resists shearing forces and the flanges resist bending forces or momentum, making the beam strong but comparatively light.

There are three main categories of I-beam: light, standard, and wide flange. The ratio of the web’s height to flange width also identifies an I-beam as a narrow, medium, or wide flanged I-beam. Light and standard I-beams are rolled differently than wide flange I-beams, although today they are often welded together. Standard I-beams are sometimes known as common, ordinary, or universal I-beams.

Light and ordinary I-beams have the same specification ratio for height to width. However, the web and flange thicknesses are narrower or thinner in a light I-beam, making it lighter in weight. The inner surface of the top and bottom flanges on both light and ordinary I-beams is inclined, so it slopes upward toward the web. The ends of the flanges are often rounded too.

The wide-flange I-beam, or H-beam, has flanges that are not sloped or only slightly inclined and the edges are typically squared. The web and flanges are welded together from metal of the same thickness, so the flanges and web are of equal thickness. Due to the common thickness, this type of beam can be oriented to form either an H or I cross-sectional profile.

Steel I-beams come in a wide range of sizes based on height, weight, width, and thickness. Engineering standards identify which type and size should be used based on strength, stability, and stiffness requirements, and whether welded, bolted, or riveted with other structural steel pieces. It is always best to leave the selection of structural steel to the professionals.

Standard I-beams can range from 3” deep by 2-3/8” wide (S3x5.7) to 24” by 8” (S24x121). Wide-flange I-beams start at 4-1/8” deep by 4” wide (W4x13) and go to 44” by 16” (W44x335). If reading the dimensions for the W44x335, the ‘W’ denotes wide flange, the 44 its depth in inches, and the 335 denotes its nominal weight in pounds per foot (lbs/ft).

Residential Steel Beam Span Table

Residential Steel Beam Span

Steel I-beams used in residential dwellings must comply with the building codes of the region the dwelling is located. A beam supporting a floor of a one-story structure often differs from one required for a two or three-story one. A beam above windows or supporting the roof will also differ due to variables too. Additionally, the spacing and span of the joists, types of supports, and all load parameters also must be factored into the selection of the beam. Since web and flange thicknesses and weight per foot of the steel determine the strength of a beam, it too is important. The Table below identifies potential span maximums for I-beams commonly used in single-story dwellings. It is best, however, to leave the selection of steel beams to a Structural Engineer.

Maximum Wide Flange I-Beam Spans for One-Story Residential Dwellings*

(depth in inches by lbs/ft)

Tributary Width with Center Beam Support
6ft 8ft 10ft 12ft 14ft 16ft 18ft 20ft 22ft 24ft
W6x9 14.3’ 13.0’ 12.0’ 11.3’ 10.8’ 10.3’ 9.8’ 9.3’ 8.9’ 8.5’
W6x12 15.8’ 14.3’ 13.3’ 12.5’ 11.9’ 11.4’ 10.9’ 10.6’ 10.2’ 9.8’
W6x16 17.9’ 16.2’ 15.1’ 14.2’ 13.5’ 12.9’ 12.4’ 12.0’ 11.6’ 11.3’
W8x10 17.6’ 16.0’ 14.9’ 14.0’ 13.2’ 12.4’ 11.7’ 11.1’ 10.6’ 10.1’
W8x13 19.2’ 17.4’ 16.2’ 15.2’ 14.4’ 13.8’ 13.1’ 12.4’ 11.9’ 11.4’
W8x15 20.4’ 18.6’ 17.2’ 16.2’ 15.4’ 14.7’ 14.2’ 13.6’ 19.9’ 12.4’
W8x18 22.2’ 20.2’ 18.7’ 17.6’ 16.8’ 16.0’ 15.4’ 14.9’ 14.4’ 14.0’
W8x21 23.7’ 21.6’ 20.0’ 18.8’ 17.9’ 17.1’ 16.5’ 15.9’ 15.4’ 15.0’
W8x24 24.5’ 22.2’ 20.7’ 19.4’ 18.5’ 17.7’ 17.0’ 16.4’ 15.9’ 15.4’
W8x28 25.9’ 23.5’ 21.8’ 20.6’ 19.5’ 18.7’ 18.0’ 17.3’ 16.8’ 16.3’
W10x12 21.2’ 19.3’ 17.9’ 16.8’ 15.6’ 14.6’ 13.8’ 13.1’ 12.5’ 11.9’
W10x15 23.0’ 20.9’ 19.4’ 18.3’ 17.4’ 16.4’ 15.5’ 14.7’ 14.0’ 13.4’
W10x17 24.4’ 22.2’ 20.6’ 19.4’ 18.4’ 17.6’ 16.7’ 15.9’ 15.2’ 14.5’
W10x19 25.7’ 23.4’ 21.7’ 20.4’ 19.4’ 18.6’ 17.9’ 17.1’ 16.3’ 15.6’
W10x22 27.6’ 25.0’ 23.2’ 21.9’ 20.8’ 19.9’ 19.1’ 18.5’ 17.9’ 17.3’
W10x26 29.4’ 26.8’ 24.8’ 23.4’ 22.2’ 21.2’ 20.4’ 19.7’ 19.1’ 18.6’
W10x30 31.1’ 28.3’ 26.2’ 24.7’ 23.5’ 22.4’ 21.6’ 20.8’ 20.2’ 19.6’
W12x14 25.0’ 22.8’ 21.1’ 19.6’ 18.2’ 17.0’ 16.1’ 15.3’ 14.6’ 13.9’
W12x16 26.3’ 23.9’ 22.2’ 20.9’ 19.4’ 18.2’ 17.2’ 16.3’ 15.6’ 14.9’
W12x19 28.5’ 25.9’ 24.0’ 22.6’ 21.5’ 20.3’ 19.2’ 18.2’ 17.4’ 16.6’
W12x22 30.2’ 27.5’ 25.5’ 24.0’ 22.8’ 21.8’ 20.9’ 19.8’ 18.9’ 18.1’
W14x22 32.8’ 29.8’ 27.7’ 26.0’ 24.7’ 23.6’ 22.3’ 21.2’ 20.2’ 19.4’
W14x26 35.1’ 31.9’ 29.6’ 27.9’ 26.5’ 25.3’ 24.4’ 23.3’ 22.3’ 21.4’

* Values derived from AISI Steel Beam Span Tables for Residential Dwellings.

What Is the Maximum Span for Steel Beam?

Maximum Span for Steel Beam

The maximum span of a steel I-beam depends on numerous factors, including the type of I-beam, depth, width, weight, flange and web thicknesses, supports, and all load variables. The location of the beam also must be factored in since one supporting 2 or more floors will differ in span and size specifications from one only supporting a roof. So, a straightforward answer isn’t something that jumps right out.

Transportation is the biggest constraint on span size. Most mills manufacture I-beams in 60 or 80-foot lengths so they can be transported on a semi-trailer. That, however, doesn’t limit the span to 60 or 80 feet since beams can be joined with plates and rivets, bolts, or welds to achieve longer unsupported spans. Presently, the longest continuous truss span in use is the Ikitsuki Bridge in Japan which has a main span of 1312 feet. The longest in the U.S. is the Astoria-Megler Bridge with a main span of 1232 feet.

Steel I Beam Span Calculator

Steel I-beam sizing should be left to a Structural Engineer as they will address all stress and load factors for the structure being designed, built, or renovated. If, however, you’re interested in seeing if an idea is feasible, we have found this calculator for uniformly loaded simple I-beams helpful.

What Is the Cost of a Steel Beam?

The size, weight, strength, and length of a steel beam are one cost, delivery is another, and installation a third. Where the beam is purchased may also affect the cost, as manufacturers and wholesalers don’t have the same markup as retailers. Additionally, steel prices fluctuate, so the price per foot can vary throughout the year in the same location.

In 2016, steel dropped to around $90 a ton from a high of $1,265 a ton in 2008. So, whether recycled or virgin steel, base material costs also affect the price per foot of the finished product. A typical I-beam used for a single-family dwelling can range from $100 to over $500 depending on all the variables. The Table below shows prices for some I-beams that may be used in residential construction. This is strictly an example since each beam listed can encompass different parameters.

Residential I-Beam Costs
I-Beam Unit Cost/Foot 20ft
W6x9 $16.20 $324.00
W6x20 $34.20 $684.00
W8x13 $23.40 $468.00
W10x12 $20.50 $410.40
W10x30 $54.00 $1080.00
W12x16 $28.80 $576.00
W24x55 $123.75 $2475.00


The distance a steel I-beam will span depends on many factors and variables. The type of beam, its depth, weight, flange width, type, thicknesses, loads, and forces all affect the span distances, as do other factors. The deeper the beam and thicker the steel used in the flanges and web, the greater its strength and weight, and the further it can span.

Most steel beams used in residential construction range from 4” to 14” deep and weigh up to 26 lbs/ft. A W14x26 can span 21’-4” and support a tributary span of 24’ depending on all variables and factors, while a W8x13 can only span 11’-4” under the same conditions. Hopefully, you have a better awareness of the factors affecting steel beam spans and how far they can span and are better prepared for your building project.

Written By: Yevgen

YevgenI'm a DIY nut, and the founder and chief editor here at Weekend Builds.
This site is a result of my DIY passion, and to share the joys I have experienced fixing, building, and creating things over the years.

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