How to do a structural steel takeoff in Australia: a step-by-step method for fab shops
A plain-English method for an Australian structural steel takeoff: read the section designation (310UB40.4), count members off the drawings, total metres and kg/m, plate by kg/m², buy in stock lengths (SHS 8 m and 12 m), allow for kerf and trim, and check the total, with a worked example from the InfraBuild Know Your Steel guide.
A structural steel takeoff is the list of every steel member on the drawings, with its section, length, quantity and weight, so you can price the job and order the right bars. Get it wrong and you either eat the cost of steel you forgot, or you carry a rack full of offcuts you paid for. This guide is the method I use, in order, with numbers from InfraBuild's Know Your Steel product guide so you can check every figure.
The short answer
- Work off the latest revision of the structural drawings and note the revision on your takeoff.
- List every member by type: beams, columns, channels, angles, hollow sections, flat bar and plate.
- Record section, length and quantity for each mark, then total the metres per section.
- Weight = metres x kg/m for sections, and m² x kg/m² for plate.
- Buy in stock lengths, not metres. Nest the pieces, allowing for saw kerf and end trim.
- Add the small stuff: cleats, stiffeners, base and cap plates, bolts, and the coating.
- Check the total against the drawings and your feel for the job before you send the price.
Step 1: Read the section designations
Australian hot-rolled sections are named by size class, type and mass per metre. A 310UB40.4 is a universal beam in the 310 class that weighs 40.4 kg/m. InfraBuild's table shows its actual size as 304 x 165 mm, so the class number isn't the true depth. Hollow sections are named by outside size and wall thickness, e.g. 100 x 100 x 4.0 SHS, which InfraBuild lists at 11.6 kg/m.
InfraBuild lists its universal beams and parallel flange channels as meeting AS/NZS 3679.1 (hot-rolled bars and sections), and its hollow sections as meeting AS/NZS 1163 (cold-formed hollow sections) in grades such as C350L0. Plate comes under AS/NZS 3678. Note the grade and finish the engineer calls up on the drawings, because a different grade or a galvanised finish can change price and availability.
Step 2: Count every member off the drawings
Go through the general arrangement, then each frame, elevation and detail. For each member mark write down the section, the length to order (not just the centre-line dimension) and how many. A simple table works:
| Mark | Section | Length (m) | Qty | Total |
|---|---|---|---|---|
| B1 | 310UB40.4 | 5.4 | 6 | 32.4 m |
| C1 | 100 x 100 x 4.0 SHS | 3.0 | 4 | 12.0 m |
| BP1 | 10 mm plate, 250 x 250 | - | 4 | 0.25 m² |
Tick members off on a printed set as you go, so nothing is counted twice or missed. Where details are repeated ("typical" connections), count how many times they occur, not once.
Step 3: Work out the weight
Steel is mostly priced by weight, so get it right:
- Sections: total metres x kg/m from the supplier table.
- Plate: area in m² x kg/m² for the thickness. InfraBuild lists 10 mm plate at 78.50 kg/m².
InfraBuild notes its masses are calculated using 7,850 kg/m³ for carbon steel and include a 2.5 per cent rolling tolerance where applicable, so use the same table you buy from. For odd shapes, see the steel weight per metre formulas.
Step 4: Buy in stock lengths, not metres
This is where most takeoffs lose money. You can't buy 12.0 m of SHS in four bits; you buy bars. InfraBuild lists 8.0 m and 12 m standard lengths for many SHS sizes, and 10 mm plate in sheet sizes such as 1800 x 6000, 2400 x 6000 and 2400 x 9000 mm. Beams and channels are shown as "various standard lengths", so ring your supplier for what's on the rack.
Then nest the cut pieces into those lengths, allowing for the saw blade (kerf) and squaring off each end. The cut list nesting guide and the free cut list checklist cover this in detail.
Worked example
A small mezzanine frame using the table above:
- 310UB40.4: 32.4 m x 40.4 kg/m = 1,309 kg
- 100 x 100 x 4.0 SHS: 12.0 m x 11.6 kg/m = 139 kg
- 10 mm base plates: 4 x 0.25 m x 0.25 m = 0.25 m² x 78.5 kg/m² = 20 kg
- Total about 1,468 kg before cleats, bolts and coating.
Now the ordering. Four 3.0 m posts are exactly 12 m, but one 12 m length won't give you four full 3.0 m pieces once kerf and trim are taken out, so you'd need two 12 m lengths (24 m bought). Two 8.0 m lengths give two posts each with room for kerf and trim (16 m bought). Same weight on the drawings, 8 m less steel on the invoice. Do the same check for the beams against the lengths your supplier holds.
Step 5: Don't forget the small stuff
- Cleats, stiffeners, end plates, cap plates and gussets (often only shown in details).
- Bolts, nuts, washers and chemical or cast-in anchors.
- Coating: primer, paint system or hot-dip galvanizing.
- Waste allowance and offcuts you can't reuse.
- Inspection and test requirements for the job. On AS/NZS 5131 projects the ITP and welding procedures add hours you should price.
Step 6: Check it before you price it
- Is the takeoff on the latest drawing revision?
- Does every mark on the drawings appear in the list?
- Are repeated "typical" details multiplied by how often they occur?
- Are kg/m figures from the same supplier table you'll buy from?
- Is the order in whole stock lengths, with kerf and trim allowed?
- Are plates, cleats, bolts and coating in?
- Does the total weight look sensible for the size of the job?
Common questions
What does 310UB40.4 mean?
It's an Australian universal beam in the 310 depth class with a nominal mass of 40.4 kg per metre. The actual section in the InfraBuild Know Your Steel guide is 304 mm deep by 165 mm wide, so the class number isn't the exact depth. For a takeoff the useful part is the last number: metres times 40.4 gives the weight in kilograms.
How do you work out the weight of steel for a takeoff?
Multiply the total length of each section by its mass per metre (kg/m) from the supplier's tables, and work out plate as area in square metres times the kg/m² for its thickness (10 mm plate is 78.5 kg/m²). InfraBuild notes its masses are based on 7,850 kg/m³ for carbon steel and include a 2.5 per cent rolling tolerance where applicable.
What stock lengths does SHS come in?
InfraBuild's Know Your Steel guide lists 8.0 m and 12 m standard lengths for many square hollow sections, such as 100 x 100 x 4.0 SHS. Beams and channels are listed as 'various standard lengths', so ask your supplier what they actually hold before you nest the cut list.
Should a takeoff order total metres or whole lengths?
Whole lengths. Total metres tells you the weight, but you buy bars, so nest the cut pieces into stock lengths, allowing for saw kerf and end trim. Four 3.0 m posts are 12 m of steel, but you can't cut four full 3.0 m pieces out of one 12 m length once kerf and trim are taken out.
Is a steel takeoff the same as a cut list?
No. The takeoff is the quantities and weights for pricing and ordering, measured from the drawings. The cut list is the shop list of every piece and length to cut. A good takeoff feeds the cut list, and the cut list then sets the final order.
Sources
- InfraBuild – Know Your Steel product reference guide (section masses, standard lengths, plate kg/m²)
- Australian Steel Institute – industry resources and section information
- Standards Australia – AS/NZS 3679.1, AS/NZS 1163, AS/NZS 3678 and AS/NZS 5131 (purchase required)
Related guides
- Steel weight per metre formulas
- Steel cut list nesting and DXF plasma files
- Free steel cut list checklist
- Steel cut list calculator
- How to quote a job with GST
- What goes in a fabrication ITP
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General information only, summarised from the official sources above as at the review date. It isn't legal, tax, WHS or engineering advice. Rules change and your situation may differ, so check the source or ask a professional.