Rolled shapes like W beams and channels come with a tabulated weight in the designation. Plate, bar, and tube cut to custom sizes don't, and a lot of a misc metals takeoff is exactly that: base plates, gussets, stiffeners, flat bar straps, round bar anchor rods, and tube framing. For those you need the formulas.
Every formula on this page comes from one number: the weight of steel per unit volume.
The Two Constants
Imperial: 3.4028 lb per foot, per square inch of cross-section.
Steel weighs about 490 lb/ft³. A bar 1 in² in cross-section and 1 ft long has a volume of 12 in³, and 490 × 12 / 1,728 = 3.4028 lb. So:
lb/ft = cross-sectional area (in²) × 3.4028
Metric: 0.00785 kg per meter, per square millimeter.
Steel density is 7,850 kg/m³. A bar 1 mm² in section and 1 m long is 0.000001 m³, which weighs 0.00785 kg. So:
kg/m = cross-sectional area (mm²) × 0.00785
Everything below is just the area of the shape plugged into one of those two lines. To convert between the systems, 1 lb/ft = 1.48816 kg/m.
Published bar and plate tables sometimes use a slightly different density (489.6 lb/ft³ is common), so your answer may differ from a mill table in the third or fourth significant figure. That's normal. For rolled shapes and HSS, always use the tabulated AISC weight rather than computing your own; the reasons are covered in our beam weight guide.
Quick Reference: All the Formulas
| Shape | Imperial (lb/ft or psf) | Metric (kg/m or kg/m²) |
|---|---|---|
| Plate (per sq ft / sq m) | 40.8336 × t (in) | 7.85 × t (mm) |
| Flat bar | w × t × 3.4028 | w × t × 0.00785 |
| Square bar | a² × 3.4028 | a² × 0.00785 |
| Round bar | d² × 2.6726 | d² × 0.006165 |
| Rectangular / square tube (sharp-corner approx.) | [2t(H + B) − 4t²] × 3.4028 | [2t(H + B) − 4t²] × 0.00785 |
| Round tube / pipe | 10.69 × (OD − t) × t | 0.02466 × (OD − t) × t |
Dimensions: t = thickness, w = width, a = side of square, d = diameter, H and B = outside height and width, OD = outside diameter. Use inches for imperial and millimeters for metric.
The round constants come from π/4 × 3.4028 = 2.6726, π × 3.4028 = 10.69, and the matching metric values π/4 × 0.00785 = 0.006165 and π × 0.00785 = 0.02466.
Plate
psf = 40.8336 × thickness (in), which most people round to 40.8. It's the same 3.4028 constant times 12 (a 12 in. wide strip, 1 ft long, is 1 sq ft).
Worked example, a 1/2 in. plate, 4 ft × 8 ft:
- Weight per square foot: 40.8336 × 0.5 = 20.42 psf
- Area: 4 × 8 = 32 sq ft
- Weight: 20.42 × 32 = 653 lb
Worked example, a base plate 14 in. × 14 in. × 1 in.:
- Area: 14 × 14 / 144 = 1.361 sq ft
- Weight: 1.361 × 40.8336 = 55.6 lb each
Bolt holes take a little off, but most estimators ignore them for base plates and carry the gross rectangle, since the drop around the plate is scrap anyway. Our steel plate weight chart has thickness-by-thickness values.
Metric: kg/m² = 7.85 × thickness (mm). A 10 mm plate is 78.5 kg/m².
Flat Bar
Flat bar is a thin rectangle priced by the foot, so use the per-foot form:
lb/ft = width (in) × thickness (in) × 3.4028
Worked example, 4 in. × 1/2 in. flat bar, 20 ft:
- Area: 4 × 0.5 = 2.0 in²
- Weight per foot: 2.0 × 3.4028 = 6.81 lb/ft
- Weight: 6.81 × 20 = 136 lb
Metric example, 200 mm × 10 mm flat: 2,000 mm² × 0.00785 = 15.7 kg/m.
Square Bar
lb/ft = side² × 3.4028
A 1 in. square bar is 3.40 lb/ft. A 1-1/2 in. square bar is 2.25 in² × 3.4028 = 7.66 lb/ft.
Round Bar
lb/ft = diameter² × 2.6726
Worked example, 1-1/4 in. round bar (a typical anchor rod size), 18 in. long:
- Weight per foot: 1.25² × 2.6726 = 1.5625 × 2.6726 = 4.18 lb/ft
- Length: 1.5 ft
- Weight: 4.18 × 1.5 = 6.3 lb each, before nuts and washers
A 1 in. round bar is 2.67 lb/ft.
Metric example, 20 mm round bar: 20² × 0.006165 = 2.47 kg/m, the same value you'll see for 20 mm rebar.
Rectangular and Square Tube
For a tube with outside dimensions H × B and wall t, the area of a sharp-cornered box is:
area ≈ 2t(H + B) − 4t²
Then multiply by 3.4028. Real tubes have rounded corners, so this formula runs a few percent high. That's the reason to use the AISC tabulated weight for any standard HSS size.
Worked example, HSS6x6x1/4 (nominal wall 0.250 in.):
- Area: 2 × 0.25 × (6 + 6) − 4 × 0.25² = 6.0 − 0.25 = 5.75 in²
- Weight: 5.75 × 3.4028 = 19.57 lb/ft
- AISC tabulated weight: 19.02 lb/ft, so the formula is about 3% heavy
Worked example, HSS10x4x1/4: 2 × 0.25 × 14 − 0.25 = 6.75 in² × 3.4028 = 22.97 lb/ft. AISC lists 22.42, again about 2.5% over.
Metric example, 100 × 100 × 5 SHS: 2 × 5 × 200 − 4 × 25 = 1,900 mm² × 0.00785 = 14.9 kg/m. Published section tables list 14.7 kg/m for the hot-finished UK section (EN 10210) and 14.2 kg/m for the AS/NZS 1163 cold-formed section, because cold-formed tube has larger corner radii. Same nominal size, different product, different weight. The HSS sizes guide and the European sections guide cover those families.
Use the formula for non-standard fabricated boxes, or as a sanity check on a quote. Don't use it in place of the table for a standard HSS.
Round Tube and Pipe
lb/ft = 10.69 × (OD − t) × t
This is the plain-end weight formula in ASME B36.10M, and unlike the rectangular tube formula it needs no corner approximation, so it matches the tables closely.
Worked example, HSS6.625x0.280:
- 10.69 × (6.625 − 0.280) × 0.280 = 10.69 × 6.345 × 0.280 = 18.99 lb/ft
- AISC tabulated weight: 18.99 lb/ft
Metric example, CHS 114.3 × 6.3: 0.02466 × (114.3 − 6.3) × 6.3 = 16.8 kg/m, which matches the catalog value.
For pipe, which is named by nominal size rather than OD, look up the real OD and wall first. A "6 inch" pipe is 6.625 in. OD. Our steel pipe schedule chart lists them for every size.
Putting It Together in a Takeoff
A typical misc metals item combines several of these. Take a column base: one base plate, four anchor rods, and two stiffeners.
Stated assumptions: base plate 14 × 14 × 1 in., anchor rods 3/4 in. diameter × 18 in., stiffeners 6 × 6 × 3/8 in. (treated as full rectangles).
| Part | Math | Weight each | Qty | Total |
|---|---|---|---|---|
| Base plate | 1.361 sq ft × 40.8336 psf | 55.6 lb | 1 | 55.6 lb |
| Anchor rod | 0.75² × 2.6726 × 1.5 ft | 2.3 lb | 4 | 9.0 lb |
| Stiffener | (36 / 144) sq ft × 40.8336 × 0.375 | 3.8 lb | 2 | 7.7 lb |
| Total | 72.3 lb |
Multiply by the number of columns and you have the base package weight. Add your waste allowance for plate drop and bar cut-off; see waste factors in steel fabrication.
Estimating only. These formulas give weight for takeoffs and pricing. Plate thickness, bar size, and anchor rod embedment are the engineer's decisions.
Steelflo pulls plate, bar, tube, and shape callouts off your PDF drawings into a takeoff you review and export, so you spend your time checking the numbers rather than typing them. See how it works.
Frequently Asked Questions
What is the formula for steel weight per foot?
Multiply the cross-sectional area in square inches by 3.4028. That constant is the weight of a 1 in² steel bar 1 ft long at 490 lb/ft³. For example, a 4 in. × 1/2 in. flat bar has 2 in² of area and weighs 6.81 lb/ft.
How do I calculate the weight of a steel plate?
Multiply the thickness in inches by 40.8336 to get pounds per square foot, then multiply by the plate's area in square feet. A 1/2 in. plate is 20.42 psf, so a 4 ft × 8 ft sheet weighs about 653 lb.
What is the formula for round bar weight?
Weight in lb/ft is diameter squared (in inches) times 2.6726. A 1 in. round bar weighs 2.67 lb/ft. In metric, kg/m is diameter squared (in mm) times 0.006165.
How do I calculate steel weight in kg per meter?
Multiply the cross-sectional area in square millimeters by 0.00785, which comes from a steel density of 7,850 kg/m³. A 200 mm × 10 mm flat bar is 2,000 mm² and weighs 15.7 kg/m.
Why doesn't my tube weight match the AISC table?
The simple rectangular tube formula assumes sharp corners, while real HSS has rounded corners, so the formula comes out a few percent heavy. For HSS6x6x1/4 it gives 19.57 lb/ft against the AISC value of 19.02. For standard sections, use the tabulated weight.