If you want to know how to calculate structural steel tonnage, the core idea is simple: list every piece, multiply its length by its weight per foot, and add it up. The craft is in what you list. Steel packages are priced by the ton, so a missed plate, a forgotten brace or an unmeasured connection moves the price directly. This guide shows how to build a steel takeoff from structural drawings, how to weigh shapes and plates, how to handle connections and deck, and how to turn the result into a bid you can defend.
If you would rather have a steel takeoff prepared from your drawings, our metals estimating services deliver tonnage by shape, deck, joists and miscellaneous metals. If you want the method first, keep reading. For a shorter introduction, see our overview of metal takeoff and steel estimating.
What goes into a structural steel takeoff
Metals work is spread across several MasterFormat sections, and your scope decides which ones you carry:
- Structural steel framing, typically 05 12 00: columns, beams, girders, bracing, base plates and connections.
- Metal joists, typically 05 21 00: open-web joists and joist girders, with bridging.
- Metal decking, typically 05 31 00: roof deck, floor deck and composite deck, with accessories.
- Metal fabrications, typically 05 50 00: stairs, railings, ladders, lintels, embeds, bollards, supports and similar items.
Surface preparation, coatings, galvanizing and fireproofing are related items that may be in a different division. Decide early what your bid covers and state what it does not.
Step 1: Collect the drawings and specifications
Steel information appears on foundation plans, framing plans, elevations, sections, details and schedules. Gather:
- Framing plans for every level and the roof, with member marks and sizes.
- Elevations and sections for column heights, bracing and splices.
- Column schedules, base plate schedules and anchor rod layouts.
- Connection details and general notes, which set bolt types, weld requirements, coatings and tolerances.
- Architectural drawings for stairs, rails, canopies, lintels and supports that attach to the structure.
- The specification, for materials grades, shop finishes, galvanizing, inspection and delegated design.
Our guide to reading construction plans for estimating explains how to compare sheets so that elements shown on only one discipline are not missed.
Step 2: Weigh rolled shapes
Rolled steel shapes are designated by type, size and weight per foot. A W12 x 26 is a wide-flange shape about 12 inches deep that weighs 26 pounds per foot. An HSS, angle or channel has its own designation and its own published weight per foot. The weights come from the AISC Steel Construction Manual shape tables, which are the standard reference for estimators, and the American Institute of Steel Construction at aisc.org publishes them along with the specifications for fabrication and erection.
The formula is: weight in pounds = length in feet x weight per foot x quantity. Group members by mark and size so that you measure each one only once, then multiply by the count. Divide by 2,000 to convert pounds to short tons, which is the unit most steel packages use.
Measure length to the cut length of the member, not just the grid-to-grid dimension. Beams framing between girders are shorter than the grid span, and columns run from the top of the base plate to the splice or to the top of the connection. If your drawings do not give cut lengths, use the grid dimension and add an allowance for end connections.
Step 3: Weigh plates and other flat pieces
Plate weight depends on thickness. Steel weighs about 490 pounds per cubic foot, so one square foot of plate, 1 inch thick, weighs about 40.8 pounds. For any thickness, multiply by the thickness in inches:
- 3/8 inch plate: 0.375 x 40.8 = about 15.3 lb per sq ft.
- 1/2 inch plate: about 20.4 lb per sq ft.
- 3/4 inch plate: about 30.6 lb per sq ft.
- 1 inch plate: about 40.8 lb per sq ft.
Weigh plates from the rectangle the piece is cut from, not from its net area, because the cut-off material is still purchased. Use the same approach for gusset plates, stiffeners, base plates, cap plates and shear tabs when you decide to count them individually. Round bar, square bar and flat bar also have published weights per foot in the manual.
Step 4: Add connections and fabrication details
Connection material, such as clip angles, shear tabs, bolts, stiffeners and weld metal, is not usually drawn piece by piece on the framing plans. Estimators handle it in one of two ways. The first is to count and weigh typical connections by type and multiply by the number of connections of each type. The second is to apply an allowance as a percentage of the weight of the main members. The allowance varies with the complexity of the framing: simple shear connections need far less than moment connections, heavy bracing connections or complex trusses. Many estimators carry somewhere between 5 and 15 percent, but the right figure comes from your own detailing and fabrication history, or from a fabricator who has priced similar frames.
Also account for coping and notching, camber, holes and slotted holes, field splices, and welded details, since they drive fabrication labor even when they do not change tonnage.
Step 5: Count bolts, anchor rods and shear studs
These small items are easy to leave off and expensive to fix later:
- High-strength bolts by diameter and length, taken from connection types or as an allowance per ton.
- Anchor rods, nuts and washers, counted from the anchor rod plan, and whether they are set by the concrete contractor or by the steel erector.
- Headed shear studs on composite beams, counted from the studs shown per beam, with stud welding labor.
- Embedded plates and angles cast into concrete, which may be furnished by the steel fabricator but installed by another trade.
Anchor rods and embeds are the classic scope gap between steel and concrete. See our guide on how to calculate concrete yardage, rebar and formwork for the concrete side.
Step 6: Price joists, deck and miscellaneous metals
Joists are counted by mark and length, since the joist manufacturer usually quotes the whole package based on the joist schedule, including bridging, extended ends and top-chord extensions. Joist girders and heavy joists need their own lines.
Metal deck is measured in square feet by type, depth and gauge, with allowances for end laps, side laps, cut-outs and waste, and with accessories such as closure strips, cover plates, pour stops and support angles. Composite floor deck also needs the concrete and the shear studs from the steel and concrete packages.
Miscellaneous metals are the items that never appear on the structural sheets: stairs, railings, ladders, bollards, lintels, shelf angles and equipment supports. Many are scattered across architectural, mechanical and site drawings. Build a miscellaneous metals list by walking every sheet, and be explicit about who supplies lintels and shelf angles for masonry, which is covered in our guide on how to calculate CMU block and brick quantities.
Step 7: Finishes, coatings and fireproofing
Shop primer, field-applied paint, galvanizing, intumescent coatings and sprayed fire-resistive material (SFRM) are priced by weight, by surface area or by linear feet of member, depending on the contractor. Galvanizing is commonly priced per ton or per pound by the galvanizer, so you need the weight of items to be galvanized, plus allowance for handling and distortion. Fireproofing is often a separate trade, so confirm whether it is in or out of your scope.
Step 8: Delivery, erection and lead times
Add shop drawings, engineering for delegated connection design, mill and fabrication lead times, shipping, field bolting and welding, crane or lift costs, temporary bracing, plumbing up of columns, grouting of base plates, and inspection. Material prices and lead times for steel can move quickly, so check current quotes and allow for escalation. Our posts on tariffs and material price changes and long-lead procurement planning explain how to account for these in a bid.
A worked example
These numbers are illustrative. A small single-story building frame has twenty W12 x 26 beams at 30 feet long, twelve W14 x 48 columns at 18 feet high, and a 16 x 16 inch base plate, 3/4 inch thick, under every column.
- Beams: 20 x 30 ft x 26 lb/ft = 15,600 lb.
- Columns: 12 x 18 ft x 48 lb/ft = 10,368 lb.
- Base plates: 16 x 16 in = 1.778 sq ft x 30.6 lb/sq ft = about 54.4 lb each x 12 = about 653 lb.
- Main material: 15,600 + 10,368 + 653 = 26,621 lb.
- Connection allowance at 8 percent: about 2,130 lb.
- Total: about 28,751 lb, which is about 14.4 tons.
If the roof is 6,000 square feet of metal deck, add 5 percent for laps and cutting, or about 6,300 square feet of deck to price. Anchor rods, bolts, shop paint, erection, deck accessories and any joists are then separate lines.
Cross-checks that catch errors
- Compare pounds of steel per square foot of floor area against similar completed buildings from your own records. A wide gap is a reason to re-check the takeoff.
- Count total members by mark, then check against the framing plans one bay at a time.
- Review the connection allowance against the type of framing, and ask the fabricator if the figure seems high or low.
- Confirm that every member on the elevations and sections is also on a plan.
Common structural steel takeoff mistakes
- Taking off only the main members and leaving connection material out of the tonnage.
- Using net plate area instead of the cut rectangle.
- Missing bracing, outriggers, canopy framing and equipment supports shown on other sheets.
- Leaving out shear studs, anchor rods, bolts and deck accessories.
- Assuming lintels, embeds and miscellaneous steel are in another scope without writing it down.
- Ignoring coatings, galvanizing and fireproofing, or pricing them without the weight or area.
- Not allowing for delivery, crane time, bracing and lead times.
These errors and others are listed in our guide to common construction estimating mistakes. For labor rates and burdens used with steel erection, see construction labor cost estimating.
Frequently asked questions
How do I convert pounds of steel to tons?
Divide by 2,000 for short tons, which is the standard unit in US steel packages. A metric ton is 2,204.6 pounds, so be sure which one a supplier is quoting.
How do I find the weight of a W-shape?
Read it from the designation. The number after the x is the weight in pounds per foot, so a W12 x 26 weighs 26 pounds per foot. Check the AISC shape tables for other shapes such as HSS, angles and channels.
How much steel does a plate weigh?
About 40.8 pounds per square foot per inch of thickness. A 1/2 inch plate weighs about 20.4 pounds per square foot.
What allowance should I add for connections?
It varies with the framing. Simple shear connections need less, and moment frames and heavy braces need more. Many estimators use a range of about 5 to 15 percent, but your fabricator or detailer is the best source for a specific project.
Is metal deck part of the steel tonnage?
No. Deck is measured in square feet and priced separately, along with accessories, shear studs and any concrete topping.
Who supplies anchor rods?
It depends on the contract. They are often furnished by the steel fabricator and installed by the concrete or the steel contractor. State your assumption in the bid.
Get a steel takeoff prepared from your drawings
We extract structural steel by shape and mark, plates, connections, joists, deck, miscellaneous metals and accessories, so you can apply current mill, fabricator and erector pricing. See our metals estimation service, our quantity and material takeoffs, or the full list of estimating services by trade. For the unit conversions used in this post, read our guide to takeoff units of measure and conversions.