Direct Answer
Structural steel fabrication cost has five components: material cost (tons × price/ton), connection material (typically 15–25% of structural material cost), labor (shop hours × burdened rate), overhead (shop burden — equipment, facility, supervision), and profit. For a quick estimate, all-in fabricated steel runs $3,000–$6,000/ton for standard commercial work; complex connections, seismic, or specialty coatings push toward $6,000–$10,000/ton.
Full Explanation
Labor estimation: assign shop hours by member type. Simple beams: 1–2 hours each. Complex assemblies: 4–8 hours. Moment connections: 6–12 hours per connection. Miscellaneous steel (stairs, rails, embeds): 15–25 shop hours/ton on average. Apply a burdened labor rate (including benefits, payroll taxes, shop overhead per direct labor hour). Add detailing cost if you're including detailing in your bid. Material: use the BOM weight × current price + freight. Connection hardware: BOM pricing for bolts, weld wire, consumables.
What This Means for Your Shop
Accuracy of your estimate depends entirely on accuracy of your BOM weight and your labor hour assumptions. If you're bidding a project type you haven't done before (say, seismic moment frames), your labor hours will be understated — budget for learning and QC overhead.
Common Mistakes
Underestimating miscellaneous steel labor. Miscellaneous items (stairs, embeds, pipe supports) are individually simple but highly variable and labor-intensive per ton relative to structural steel. Using the same $/ton factor for misc. as structural is a common underestimation error.
Recommended Process
Develop a historical database of your actual shop hours per assembly type from completed projects. Use this as your estimating baseline. Adjust for project-specific factors (seismic premium, coating complexity, schedule pressure).