Steel Beam Span Quick Reference — W-Shape Spans for Floor & Roof Loads

Quick-reference beam span tables for W-shapes under typical floor and roof loading conditions. Provides maximum simply supported spans for the 50 most commonly used W-shapes at standard beam spacings of 6 ft, 8 ft, and 10 ft. Spans are limited by both flexural strength (ASD allowable stress) and deflection (L/360 live load for floors, L/240 for roofs).

These tables are for preliminary sizing and feasibility studies. They assume ASTM A992 steel (Fy = 50 ksi), continuously laterally braced compression flanges, and simply supported conditions. For final design, detailed calculations per AISC 360 are required.

Using These Span Tables

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

1. Determine the tributary width supported by the beam (typically half the distance to adjacent beams on each side).
2. Find your load condition (total load = dead + live). For composite floors: typical total load = 65-85 psf (15-20 psf deck/concrete + 50 psf live). For roofs: typical total load = 35-60 psf (15-20 psf dead + 20-40 psf live/snow).
3. Select beam spacing (6, 8, or 10 ft) matching your framing layout.
4. Read the maximum span from the table. The span shown is the center-to-center distance between supports.
5. Check serviceability: If tighter deflection limits apply (L/480 for sensitive floors, L/600 for masonry-supported beams), reduce the tabulated spans by 10-20%.

Load Assumptions

Beam Spans — 6 ft Beam Spacing (Light Framing)

Typical for residential, multi-family, and light commercial where tighter spacing reduces floor thickness. Tributary width = 6 ft. Total uniform load = 6 ft * (15 psf DL + 50 psf LL) = 390 plf for floors (390 plf = 0.39 kip/ft).

Floor Beams at 6 ft Spacing (50 psf Live Load, L/360)

Roof Beams at 6 ft Spacing (20 psf Live Load, L/240)

Total uniform load = 6 ft * (15 psf DL + 20 psf Lr) = 210 plf.

Beam Spans — 8 ft Beam Spacing (Standard Commercial)

Most common beam spacing for commercial office buildings. Tributary width = 8 ft. Total uniform load = 8 ft * (15 psf DL + 50 psf LL) = 520 plf (0.52 kip/ft).

Floor Beams at 8 ft Spacing (50 psf Live Load, L/360)

Roof Beams at 8 ft Spacing (20 psf Live Load, L/240)

Total uniform load = 8 ft * (15 psf DL + 20 psf Lr) = 280 plf. Deflection limit L/240.

Beam Spans — 10 ft Beam Spacing (Wide Spacing)

Used for long-span structures where minimizing column count is the priority. Tributary width = 10 ft. Total uniform load = 10 ft * (15 psf DL + 50 psf LL) = 650 plf (0.65 kip/ft).

Floor Beams at 10 ft Spacing (50 psf Live Load, L/360)

Heavy Load Spans — 100 psf Total Load (Storage, Assembly, Corridor)

For heavy occupancy conditions: corridors (100 psf live load), assembly areas, light storage. Total load = 100 psf assumed (80 LL + 20 DL or 100 LL + 15 DL).

Floor Beams at 8 ft Spacing, 100 psf Total Load, L/360

Beam Span Selection Workflow

For a typical project, follow this sequence:

1. Determine beam tributary width. For a 40 ft wide building with 5 equal bays: beam spacing = 40/5 = 8 ft.
2. Calculate total uniform load. w = spacing _ (DL + LL). For 8 ft spacing at 65 psf total: w = 8 _ 65 = 520 plf = 0.52 kip/ft.
3. Identify maximum span from architectural constraints. Column grid determines the beam span.
4. Select a W-shape from the table that meets or exceeds the required span. Always check the deflection column — if near the limit, consider the next deeper section.
5. Check minimum depth for deflection serviceability: For L/360: minimum depth approx = L/24 for composite beams, L/20 for non-composite. For a 30 ft span, min depth = 30*12/24 = 15 inches, suggesting W14 to W16 minimum.
6. Verify with detailed calculations using the AISC 360 code checks or our beam capacity calculator.

Common Beam Depth Ranges by Span

Frequently Asked Questions

Why do deeper beams span further? The moment of inertia Ix scales approximately with d^3 (depth cubed). Doubling the depth multiplies the stiffness by approximately 8 (since I = bt(d/2)^2 = (bt/4)d^2 for the flange contribution plus web). A W24x55 (d = 23.57 in, Ix = 1,350) is about 3.2 times stiffer than a W12x26 (d = 12.22 in, Ix = 204), which closely follows the d^3 relationship: (23.57/12.22)^3 = 7.2, adjusted for the different flange areas. This is why increasing depth is the most efficient way to increase beam span.

How much does increasing beam weight help span? Adding weight to a beam (going from W21x44 to W21x62 at the same depth) increases Ix from 761 to 1,210 in^4 (59% increase) for a 41% weight increase. The Ix increase comes from thicker flanges and a thicker web. For deflection-limited beams, going heavier at the same depth provides diminishing returns — consider going to the next depth instead. A W24x55 (1,350 in^4, 55 lb/ft) provides more stiffness than a W21x62 (1,210 in^4, 62 lb/ft) at lower weight.

When should I use composite vs non-composite beams? Composite beams achieve 30-50% longer spans or 25-35% lighter sections by engaging the concrete slab as part of the compression flange. For span-to-depth ratios above 24 (e.g., 30 ft span with 15 in deep beam = ratio of 24), composite construction is strongly recommended. For ratios below 20, non-composite may be more economical when considering the cost of shear studs and installation. These span tables assume non-composite behavior for conservative preliminary sizing. For composite design, spans can be increased by approximately 25-35%.

What if my beam has point loads instead of uniform load? For a single point load at midspan, the equivalent uniform load is 2 _ P/L (where P is the point load and L is the span). For two equal point loads at third points, equivalent uniform load = 3 _ P/L. If your loading is predominantly point loads, enter the tables with the equivalent uniform load. Be aware that point loads also concentrate shear at load points — check web yielding and crippling at the load application points per AISC 360 J10.

How do I adjust spans for different steel grades? These tables assume Fy = 50 ksi (A992). For Fy = 36 ksi (A36): flexural strength reduces by approximately 28% (36/50 = 0.72), so reduce spans by approximately 10-15% for strength-controlled beams. Deflection is independent of Fy (same E = 29,000 ksi for all grades), so deflection-limited beams have identical spans regardless of grade.

Try it now: Calculate beam spans with our free beam capacity calculator

Related Pages

• Section Properties Quick Reference — Full W-shape property tables
• Steel Beam Span Guide — Detailed — Detailed span calculations with load cases
• Beam Design Example — Step-by-step AISC 360 beam design
• Deflection Limits — Code-specified deflection criteria
• Steel Beam Load Tables — Pre-calculated capacity tables

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All spans are preliminary approximations and must be verified by a licensed Professional Engineer using project-specific loads, geometry, and boundary conditions. The site operator disclaims liability for any loss arising from use of this information.

Design Resources

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Design guides

• Steel Beam Design Workflow
• Composite Beam Design
• Roof Framing Design