How do you calculate steel flat bar weight per foot?

Steel flat bar weight per foot is calculated using: Weight (lb/ft) = Width (in) × Thickness (in) × 3.40, where 3.40 = 490 lb/ft³ (steel density) ÷ 144 in²/ft². For metric: Weight (kg/m) = Width (mm) × Thickness (mm) × 0.00785, where 0.00785 = 7,850 kg/m³ ÷ 1,000,000. Examples: a 4" × 1/4" flat bar weighs 4 × 0.25 × 3.40 = 3.40 lb/ft; a 6" × 3/8" bar weighs 6 × 0.375 × 3.40 = 7.65 lb/ft; a 100mm × 10mm flat bar weighs 100 × 10 × 0.00785 = 7.85 kg/m. Standard thickness increments are 1/8" (0.125"), 3/16" (0.1875"), 1/4" (0.250"), 5/16" (0.3125"), 3/8" (0.375"), 1/2" (0.500"), 5/8" (0.625"), 3/4" (0.750"), 1" (1.000"), 1-1/4" (1.250"), 1-1/2" (1.500"), and 2" (2.000"). Widths range from 3/4" to 12". For non-standard thicknesses, use the formula directly. Actual mill tolerance is ±0.006" to ±0.030" on thickness depending on width per ASTM A6. For design, use the nominal dimensions per the AISC Steel Construction Manual Table 1-34 for flat bars, which lists full section properties including I, S, r for both axes.

What are the common applications for steel flat bars in construction?

Steel flat bars serve versatile structural and non-structural applications: (1) Connection brackets and clips — 1/4" × 3" to 1/2" × 6" flat bars for angle seat connections, stiffener plates, and bearing plates. (2) Tension ties and straps — 1/8" × 1" to 1/4" × 4" for light tension members in bracing systems. (3) Base plates for small columns — 1/2" to 1" thick flat bars cut to size, cheaper than ordering custom plate sizes. (4) Stiffeners for beam and column connections — 3/8" × 4" to 3/4" × 8" flat bar stiffeners fillet-welded to beam webs and column flanges. (5) Shim packs — thin flat bars (1/8" to 1/4") used to adjust bearing elevation at base plates and beam seats. (6) Lintel angles — 1/4" × 3" to 3/8" × 6" flat bars used horizontally as shelf angles. (7) Girts and purlins — flat bars used as sag rods and bridging between open-web joists, typically 1/4" × 1" to 3/8" × 1-1/2". (8) Spacers and fillers — between back-to-back angles or channels. Flat bars are limited in compression due to buckling about the weak axis (r_min ≈ 0.289 × thickness); for compression applications, the unbraced length should not exceed approximately 40 × thickness for Fy = 36 ksi.

What ASTM specifications cover steel flat bars?

Steel flat bars are produced to the following ASTM specifications: ASTM A36 — the default structural specification for flat bars up to 8" thick (though flat bars are rarely used beyond 2" thick), with Fy = 36 ksi and Fu = 58 ksi. ASTM A572 Grade 50 — higher strength flat bars (Fy = 50 ksi) for structural applications requiring 39% higher capacity per pound. ASTM A1011 SS Grade 36 — hot-rolled sheet and strip in flat bar dimensions, typical for lighter gauges (1/8" to 1/4"). ASTM A1011 HSLAS Grade 50 — high-strength low-alloy sheet for lighter gauge high-strength applications. Dimensional tolerances per ASTM A6/A6M: width tolerance ±1/16" for widths ≤ 4", ±3/32" for 4-6", ±1/8" for widths > 6"; thickness tolerance ±0.006" for 3/16" bar, to ±0.014" for 3/4" bar, to ±0.030" for 2" bar. Flat bars are distinguished from plate (width ≥ 8" or thickness ≥ 1/4" per ASTM A6 definition) and from sheet/strip (thickness < 1/4"). For design, flat bar section properties are straightforward: A = w × t, Ix = wt³/12, Iy = tw³/12, Sx = wt²/6, rx = t/√12 ≈ 0.289t, ry = w/√12 ≈ 0.289w. The weak-axis radius of gyration ry is notably large for wide flat bars used as tension members, which is why they are efficient in tension but slenderness-limited in compression.

How do you design a steel flat bar tension member?

Flat bar tension member design per AISC 360-22 follows two limit states: (1) Tensile yielding of gross section: φRn = φ × Fy × Ag = 0.90 × Fy × (w × t). For A36, this gives 0.90 × 36 × w × t = 32.4 × w × t kips. For a 4" × 1/4" bar: 32.4 × 4 × 0.25 = 32.4 kips capacity. (2) Tensile rupture of net section: φRn = φ × Fu × Ae = 0.75 × Fu × An × U. An is the net area (gross minus bolt holes plus 1/16" per AISC B4.3b). For flat bars, the shear lag factor U = 1.0 when the load is transmitted directly to each element by fasteners or welds. For a 4" × 1/4" bar with one 13/16" hole: An = 4 × 0.25 − (0.813 + 0.063) × 0.25 = 1.000 − 0.219 = 0.781 in². φRn = 0.75 × 58 × 0.781 × 1.0 = 33.9 kips. Tension rupture controls in this case (33.9 < 32.4 × 4 × 0.25 = 32.4). Block shear at the connection end must also be checked per AISC J4.3. Minimum thickness for threaded rod-end flat bar tension members: d_min ≥ √(4 × Tu / (π × φ × Fy)) for a pin hole. Also check AISC D5 for pin-connected members, with minimum edge distances per Table J3.4.

What thickness flat bar can be used as a stiffener in beam-to-column connections?

Flat bar stiffeners in beam-to-column moment connections must meet AISC 358 and AISC 360 Section J10 requirements: (1) Stiffener thickness ts should approximately match the beam flange thickness tbf — for W18 and smaller, 3/8" to 1/2" is typical; for W21-W24, 1/2" to 3/4"; for W27 and larger, 3/4" to 1". (2) Stiffener width must extend to at least the column flange toe of fillet (k1 dimension), plus adequate weld access. (3) Stiffeners are attached to the column web with fillet welds sized to develop the stiffener force: φRw = φ × 0.60 × FEXX × 0.707 × w_size × 2 × stiffener length. For E70XX electrodes: a 5/16" fillet both sides provides 13.9 kips per inch of stiffener length (5.57 kip/in per side × 2 sides). (4) The stiffener force Fst = Fyf × bf × tf from the beam flange (capacity design). For a W21 beam with 10" × 0.650" flange: Fst = 50 × 10 × 0.650 = 325 kips. Stiffener area required = 325 / (0.90 × 36) = 10.0 in²; a 3/4" × 10" flat bar stiffener pair (2 × 0.75 × 10 = 15 in²) provides adequate area. (5) Local web yielding and crippling at the stiffener ends must be checked per J10.2 and J10.3 — stiffeners are bearing stiffeners and must extend to or near the column flanges.

Steel Flat Bar Sizes — Dimensions & Weight Chart

Q: How do you design a steel flat bar tension member?

Flat bar tension member design per AISC 360-22 follows two limit states: (1) Tensile yielding of gross section: φRn = φ × Fy × Ag = 0.90 × Fy × (w × t). For A36, this gives 0.90 × 36 × w × t = 32.4 × w × t kips. For a 4" × 1/4" bar: 32.4 × 4 × 0.25 = 32.4 kips capacity. (2) Tensile rupture of net section: φRn = φ × Fu × Ae = 0.75 × Fu × An × U. An is the net area (gross minus bolt holes plus 1/16" per AISC B4.3b). For flat bars, the shear lag factor U = 1.0 when the load is transmitted directly to each element by fasteners or welds. For a 4" × 1/4" bar with one 13/16" hole: An = 4 × 0.25 − (0.813 + 0.063) × 0.25 = 1.000 − 0.219 = 0.781 in². φRn = 0.75 × 58 × 0.781 × 1.0 = 33.9 kips. Tension rupture controls in this case (33.9 < 32.4 × 4 × 0.25 = 32.4). Block shear at the connection end must also be checked per AISC J4.3. Minimum thickness for threaded rod-end flat bar tension members: d_min ≥ √(4 × Tu / (π × φ × Fy)) for a pin hole. Also check AISC D5 for pin-connected members, with minimum edge distances per Table J3.4.

Q: What thickness flat bar can be used as a stiffener in beam-to-column connections?

Flat bar stiffeners in beam-to-column moment connections must meet AISC 358 and AISC 360 Section J10 requirements: (1) Stiffener thickness ts should approximately match the beam flange thickness tbf — for W18 and smaller, 3/8" to 1/2" is typical; for W21-W24, 1/2" to 3/4"; for W27 and larger, 3/4" to 1". (2) Stiffener width must extend to at least the column flange toe of fillet (k1 dimension), plus adequate weld access. (3) Stiffeners are attached to the column web with fillet welds sized to develop the stiffener force: φRw = φ × 0.60 × FEXX × 0.707 × w_size × 2 × stiffener length. For E70XX electrodes: a 5/16" fillet both sides provides 13.9 kips per inch of stiffener length (5.57 kip/in per side × 2 sides). (4) The stiffener force Fst = Fyf × bf × tf from the beam flange (capacity design). For a W21 beam with 10" × 0.650" flange: Fst = 50 × 10 × 0.650 = 325 kips. Stiffener area required = 325 / (0.90 × 36) = 10.0 in²; a 3/4" × 10" flat bar stiffener pair (2 × 0.75 × 10 = 15 in²) provides adequate area. (5) Local web yielding and crippling at the stiffener ends must be checked per J10.2 and J10.3 — stiffeners are bearing stiffeners and must extend to or near the column flanges.

Steel flat bars are rectangular cross-section bars used for brackets, clips, straps, tie rods, base angles, and miscellaneous structural connections. This page provides standard sizes, weights, and selection guidance for hot-rolled steel flat bars.

Weight Calculation

Weight per foot (lb/ft) = width (in) × thickness (in) × 3.40

where 3.40 = 490 lb/ft³ / (12 in/ft × 12 in/ft)

Weight per foot (lb/ft) = width (in) × thickness (in) × 40.8 / 12

Standard Flat Bar Sizes and Weights

1/8 in (0.125 in) Thick

Width (in)	Weight (lb/ft)	Area (in²)	Common Use
3/4	0.32	0.094	Light straps, clips
1	0.43	0.125	Light brackets
1-1/4	0.53	0.156	Straps
1-1/2	0.64	0.188	Light ties
2	0.85	0.250	Straps, clips
2-1/2	1.06	0.313	Tie straps
3	1.28	0.375	Medium brackets
4	1.70	0.500	Medium straps

3/16 in (0.1875 in) Thick

Width (in)	Weight (lb/ft)	Area (in²)
3/4	0.48	0.141
1	0.64	0.188
1-1/2	0.96	0.281
2	1.28	0.375
2-1/2	1.59	0.469
3	1.91	0.563
4	2.55	0.750

1/4 in (0.250 in) Thick

Width (in)	Weight (lb/ft)	Area (in²)	Common Use
3/4	0.64	0.188	Clips, ties
1	0.85	0.250	Standard brackets
1-1/4	1.06	0.313	Gusset straps
1-1/2	1.28	0.375	Connection angles
2	1.70	0.500	Base angles
2-1/2	2.13	0.625	Medium brackets
3	2.55	0.750	Shear tabs (light)
4	3.40	1.000	Standard brackets
5	4.25	1.250	Heavy straps
6	5.10	1.500	Beam clips

3/8 in (0.375 in) Thick

Width (in)	Weight (lb/ft)	Area (in²)
1	1.28	0.375
1-1/2	1.91	0.563
2	2.55	0.750
2-1/2	3.19	0.938
3	3.83	1.125
4	5.10	1.500
5	6.38	1.875
6	7.65	2.250

1/2 in (0.500 in) Thick

Width (in)	Weight (lb/ft)	Area (in²)	Common Use
1	1.70	0.500	Connection plates
1-1/2	2.55	0.750	Clip angles
2	3.40	1.000	Base plates (small)
2-1/2	4.25	1.250	Gusset plates
3	5.10	1.500	Shear tabs
4	6.80	2.000	Connection plates
5	8.50	2.500	Bracket plates
6	10.20	3.000	Heavy connections

3/4 in to 2 in Thick

Width × Thickness	Weight (lb/ft)	Area (in²)
2 × 3/4	5.10	1.500
3 × 3/4	7.65	2.250
4 × 3/4	10.20	3.000
2 × 1	6.80	2.000
3 × 1	10.20	3.000
4 × 1	13.60	4.000
6 × 1	20.40	6.000
4 × 1-1/2	20.40	6.000
6 × 1-1/2	30.60	9.000
6 × 2	40.80	12.000

ASTM Specifications

Spec	Grade	Fy (ksi)	Use
A36	—	36	General purpose, most flat bar
A572	Gr 50	50	Higher strength connections
A588	—	50	Weathering, exposed applications

Most structural flat bar is A36. Availability decreases for sizes above 6 in wide or 1 in thick.

Available Lengths

Form	Standard Lengths
Cut-to-length bars	20 ft, 24 ft (mill)
Bar-in-coil	Continuous (for small sizes)
Cut pieces	Per order (1 ft to 20 ft)

Design Applications

Application	Typical Size	Design Consideration
Shear tabs	3/8 × 4 to 1/2 × 6	Check bolt bearing, block shear
Clip angles	3/8 × 2 to 1/2 × 4	Eccentricity on weld group
Base angles	1/4 × 3 to 3/8 × 4	Bolt tension and bearing
Straps and ties	1/8 × 1 to 1/4 × 3	Tension yielding and fracture
Bracket plates	1/2 × 4 to 3/4 × 6	Flexure and shear
Stiffener bars	3/8 × 3 to 1/2 × 4	Local buckling
Tie rods (flat)	1/4 × 1 to 1/2 × 2	Tension capacity

Frequently Asked Questions

What is the standard length of a steel flat bar? Mill standard is 20 or 24 feet. Steel suppliers cut to length per order. Smaller sizes may be available in coil form for continuous feeding.

What is the difference between flat bar and plate? Flat bar is rolled to specific widths (typically under 12 inches) with rounded edges. Plate is flat with square edges, available in any width. Plate is typically specified by thickness alone, while flat bar is specified by width and thickness.

How much does a 1/4 × 4 steel flat bar weigh per foot? 1/4 in × 4 in = 0.250 × 4 × 3.40 = 3.40 lb/ft.

Can flat bar be used for structural connections? Yes, flat bar is widely used for shear tabs, clip angles, gusset plates, base angles, and other connection elements. The designer must check all applicable limit states (yielding, fracture, bearing, block shear, weld capacity).

What grade of steel is flat bar? Most structural flat bar is ASTM A36 (Fy = 36 ksi). A572 Grade 50 (Fy = 50 ksi) is available for higher strength. Check with the supplier for grade certification.

Steel Plate Weight — Plate weight by thickness
Steel Weight Calculator — Weight by dimensions
Steel Gauge Thickness — Gauge to inch conversion
Bolted Connections — Connection design
Steel Weight per Foot — W, HSS, C, L weights

Disclaimer

This is a calculation tool, not a substitute for professional engineering certification. All results must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs.