Direct Answer
A material takeoff (MTO) is a quantification of all steel material required for a project — section sizes, lengths, grades, and weights — used for purchasing and estimating. For structural steel, the most accurate MTO is generated directly from the 3D detailing model (Tekla BOM). Manual takeoffs from 2D drawings are less accurate and more time-consuming, and should only be used when a model is not available.
Full Explanation
Model-generated BOMs include: every member with its section designation, material grade, length, and weight. They also include connection material (plates, angles, gussets) once connections are modeled. Manual MTO from 2D drawings involves counting members by type, measuring scaled lengths, and applying weight factors (lbs/ft from AISC section tables). Manual MTOs are typically ±10% accurate; model-generated BOMs are ±2%. The weight difference matters significantly when pricing a project.
What This Means for Your Shop
If you're bidding from design drawings without a model, your MTO accuracy is limited. Build a contingency into material pricing to cover design growth and takeoff error. For negotiated projects, push to have the detailer start modeling early so you can bid from a model BOM.
Common Mistakes
Not including miscellaneous steel (stairs, handrail, equipment supports, embeds) in the MTO. Miscellaneous items are individually small but can represent 10–15% of total project weight and a higher percentage of fabrication cost.
Recommended Process
For bid MTOs without a model: count main structural members from framing plans, apply section size and weight factor, add a 10–15% factor for connections and miscellaneous steel. For final purchasing, always use the model BOM.