How to estimate steel tonnage for industrial steel building RFQ is a common question when EPC buyers need early pricing but final shop drawings are not ready. A provisional tonnage estimate helps suppliers understand project size, prepare a reasonable quotation, and separate firm scope from assumptions.
This estimate is not a replacement for structural design or fabrication takeoff. It is a procurement control tool. The buyer should state how the tonnage was prepared, which items are included, and which items remain provisional.
1. Start from the available drawing level
The accuracy of any tonnage estimate depends on the drawing package. General arrangement drawings may support only a rough range. Structural drawings can support a better quantity. Approved shop drawings or a bill of materials can support a more detailed takeoff.
| Drawing level | Useful for RFQ | Buyer caution |
|---|---|---|
| Concept layout | Early budget range only. | State that member sizes and connections are not final. |
| Structural design drawings | Preliminary main steel and secondary steel estimate. | Connection plates, stiffeners, and accessories may change. |
| Member schedule | More reliable quantity by member type. | Confirm whether plates, bolts, and small parts are included. |
| Shop drawings | Detailed takeoff for order control. | Check revision status and approved-for-fabrication mark. |
If drawings are incomplete, first review the steel structure quotation drawing checklist.
2. Separate primary steel, secondary steel, and accessories
A useful RFQ estimate should not give only one number. Separate the main frame from secondary members and accessories so the quotation can be compared more clearly.
- Primary steel: columns, rafters, beams, trusses, crane beams, platforms, and heavy bracing.
- Secondary steel: purlins, girts, sag rods, tie rods, light bracing, ladders, handrails, and small support frames.
- Plates and connection items: base plates, gusset plates, splice plates, stiffeners, and clips.
- Fasteners and loose items: anchor bolts, high-strength bolts, washers, nuts, and small packed accessories.
When the RFQ mixes these items together, suppliers may price different scopes and the buyer may compare numbers that are not equivalent.
3. Use a simple takeoff table
For early procurement, a spreadsheet can be enough. List each member type, section size, length, quantity, unit weight, and calculated weight. Add a separate note for estimated connection plates and missing details.
| Takeoff column | What to record |
|---|---|
| Member mark or type | Column, rafter, beam, bracing, purlin, girt, platform, or plate group. |
| Section size | Profile or plate thickness shown on drawings. |
| Length and quantity | Total length or piece count from drawings and grids. |
| Unit weight | Weight per meter, per piece, or calculated plate weight. |
| Scope note | Included, excluded, provisional, or pending design confirmation. |
4. Add a contingency for incomplete details
Early estimates often miss connection plates, stiffeners, temporary lifting points, small brackets, and design changes. Instead of hiding this uncertainty, add a clearly labelled allowance and ask suppliers to quote based on the same assumption.
- Use a provisional allowance for connection plates if details are not finished.
- Show whether bolts and anchor bolts are included in the tonnage or listed separately.
- Separate cladding, doors, insulation, and civil steel if they are not part of the fabrication package.
- Ask suppliers to state whether their quotation is based on net weight, gross weight, or shipping weight.
5. Check building factors that change tonnage
Two industrial buildings with the same floor area can have very different steel weights. Procurement teams should record the project conditions that may affect tonnage before sending the RFQ.
| Factor | Why it affects steel tonnage |
|---|---|
| Span and bay spacing | Long spans and large bay spacing may require heavier members. |
| Crane system | Crane beams, brackets, lateral bracing, and service platforms add weight. |
| Wind, snow, and seismic loads | Design loads influence member size, bracing, and connection demand. |
| Mezzanine or equipment loads | Platforms, equipment supports, and floor beams increase primary steel. |
| Coating and packing scope | Does not change steel weight much, but affects quotation and shipment basis. |
6. Write the RFQ quantity note clearly
When sending an RFQ, the tonnage note should explain the basis of estimate. This reduces misunderstandings and makes later quote comparison easier.
Example quantity note: The provisional steel tonnage is prepared from current structural drawings dated [insert date]. It includes primary steel, secondary steel, and estimated connection plates. Anchor bolts, cladding, doors, and installation are excluded unless stated otherwise. Please review the drawings and identify any missing items or major quantity differences in your quotation.
The steel structure RFQ template can be used to place this quantity note inside a full quotation package.
7. Compare supplier feedback against the same baseline
After quotations are received, compare each supplier's tonnage assumption against your RFQ estimate. A lower total price may simply be based on a lower assumed steel quantity or excluded accessories.
- Ask each supplier to return a tonnage breakdown by item group.
- Compare included and excluded scope before comparing unit prices.
- Review whether connection plates and small parts are included.
- Check whether the quotation uses net fabrication weight or packed shipping weight.
- Record major quantity differences before commercial negotiation.
For the quote review stage, use the guide on how to compare steel structure fabrication quotes.
Buyer note
A steel tonnage estimate is useful only when the scope, drawing status, exclusions, and assumptions are transparent. Before contacting multiple fabricators, prepare the drawing package, define the quantity basis, and include the document and quality requirements from the EPC steel structure procurement checklist.