Flat bar shows up on almost every job, and almost never as a line on the structural plans. It hides in details: shear tab stock, stair stringer caps, handrail posts welded to base straps, embed plates, lintel bearing plates, kicker straps, and the endless "PL 3/8 x 4" callouts that are really flat bar cut from 20-foot sticks. If you price it by the pound, you need the weight per foot, and you need it fast.
This page gives you the chart, the formula so you can work any size that isn't on it, and a check against a published mill-supplier table so you know how far the numbers can be trusted.
How steel flat bar weight is calculated
Flat bar is a solid rectangle, so its weight is just cross-sectional area times the weight of steel per unit volume.
Assumption used in every table on this page: carbon steel at a density of 490 lb/ft³, which is 0.2836 lb/in³. One square inch of steel section, one foot long, is 12 in³ of steel:
- 12 in³ × 0.2836 lb/in³ = 3.40 lb per foot for every square inch of section
The unrounded value is 490 ÷ 144 = 3.4028. That gives the formula:
Weight (lb/ft) = width (in) × thickness (in) × 3.4028
Example: a 1/2" × 4" flat bar is 0.5 × 4 = 2.0 in². 2.0 × 3.4028 = 6.81 lb/ft. A 20-foot bar weighs 136 lb.
It is the same formula we use for calculating steel beam weight from section area. Flat bar is just the easy case because there are no fillets or radiused corners to worry about.
Flat bar weight chart (lb/ft)
Rows are bar width, columns are thickness. All values are calculated from the formula above at 490 lb/ft³ and rounded to two decimals.
| Width (in) | 1/8" | 3/16" | 1/4" | 5/16" | 3/8" | 1/2" | 5/8" | 3/4" | 1" |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 0.43 | 0.64 | 0.85 | 1.06 | 1.28 | 1.70 | 2.13 | 2.55 | 3.40 |
| 1-1/4 | 0.53 | 0.80 | 1.06 | 1.33 | 1.60 | 2.13 | 2.66 | 3.19 | 4.25 |
| 1-1/2 | 0.64 | 0.96 | 1.28 | 1.60 | 1.91 | 2.55 | 3.19 | 3.83 | 5.10 |
| 2 | 0.85 | 1.28 | 1.70 | 2.13 | 2.55 | 3.40 | 4.25 | 5.10 | 6.81 |
| 2-1/2 | 1.06 | 1.60 | 2.13 | 2.66 | 3.19 | 4.25 | 5.32 | 6.38 | 8.51 |
| 3 | 1.28 | 1.91 | 2.55 | 3.19 | 3.83 | 5.10 | 6.38 | 7.66 | 10.21 |
| 3-1/2 | 1.49 | 2.23 | 2.98 | 3.72 | 4.47 | 5.95 | 7.44 | 8.93 | 11.91 |
| 4 | 1.70 | 2.55 | 3.40 | 4.25 | 5.10 | 6.81 | 8.51 | 10.21 | 13.61 |
| 5 | 2.13 | 3.19 | 4.25 | 5.32 | 6.38 | 8.51 | 10.63 | 12.76 | 17.01 |
| 6 | 2.55 | 3.83 | 5.10 | 6.38 | 7.66 | 10.21 | 12.76 | 15.31 | 20.42 |
| 8 | 3.40 | 5.10 | 6.81 | 8.51 | 10.21 | 13.61 | 17.01 | 20.42 | 27.22 |
To get the weight of a full stick, multiply by 20 (standard hot-rolled flat bar ships in 20-foot lengths from most service centers). For a 3/8" × 3" bar: 3.83 × 20 = 76.6 lb per stick.
Sizes over 8" wide are usually sold as plate or universal mill (UM) plate rather than bar stock, but the formula doesn't change.
How the chart compares to a published mill table
We checked the computed values against the hot-rolled mild steel flat bar tables in Coyote Steel's No. 1 Handbook of Steel Sizes & Weights, a service-center handbook that lists estimated weight per foot for each size.
| Size (t × w) | Computed, 490 lb/ft³ | Coyote Steel handbook | Difference |
|---|---|---|---|
| 1/4" × 2" | 1.701 | 1.700 | -0.08% |
| 1/4" × 4" | 3.403 | 3.400 | -0.08% |
| 3/8" × 3" | 3.828 | 3.825 | -0.08% |
| 1/2" × 4" | 6.806 | 6.800 | -0.08% |
| 1/2" × 6" | 10.208 | 10.200 | -0.08% |
| 3/4" × 4" | 10.208 | 10.200 | -0.08% |
| 1" × 6" | 20.417 | 20.400 | -0.08% |
| 3/16" × 2" | 1.276 | 1.276 | -0.00% |
| 5/8" × 3" | 6.380 | 6.375 | -0.08% |
The handbook values run about 0.08% lighter across the board. That isn't a disagreement about the steel; it's rounding. The handbook works from 3.40 lb per square inch of section instead of 3.4028. On a 1" × 6" bar that is 0.017 lb per foot, or about a third of a pound on a 20-foot stick. Nobody will ever bill that difference, but it's worth knowing why two charts don't match to the third decimal.
Real bars also carry mill tolerances on width and thickness, and hot-rolled edges are slightly rounded, so the delivered weight of a bar will never match either number exactly. For estimating, 3.40 or 3.4028 are both fine. Pick one and use it everywhere so your takeoff and your purchase order agree.
Metric flat bar weight chart (kg/m)
For metric drawings the same logic applies with steel at 7,850 kg/m³:
Mass (kg/m) = width (mm) × thickness (mm) × 0.00785
| Width (mm) | 5 mm | 6 mm | 8 mm | 10 mm | 12 mm | 15 mm | 20 mm | 25 mm |
|---|---|---|---|---|---|---|---|---|
| 25 | 0.98 | 1.18 | 1.57 | 1.96 | 2.35 | 2.94 | 3.92 | 4.91 |
| 30 | 1.18 | 1.41 | 1.88 | 2.35 | 2.83 | 3.53 | 4.71 | 5.89 |
| 40 | 1.57 | 1.88 | 2.51 | 3.14 | 3.77 | 4.71 | 6.28 | 7.85 |
| 50 | 1.96 | 2.35 | 3.14 | 3.92 | 4.71 | 5.89 | 7.85 | 9.81 |
| 60 | 2.35 | 2.83 | 3.77 | 4.71 | 5.65 | 7.06 | 9.42 | 11.77 |
| 75 | 2.94 | 3.53 | 4.71 | 5.89 | 7.06 | 8.83 | 11.77 | 14.72 |
| 80 | 3.14 | 3.77 | 5.02 | 6.28 | 7.54 | 9.42 | 12.56 | 15.70 |
| 100 | 3.92 | 4.71 | 6.28 | 7.85 | 9.42 | 11.77 | 15.70 | 19.62 |
| 120 | 4.71 | 5.65 | 7.54 | 9.42 | 11.30 | 14.13 | 18.84 | 23.55 |
| 150 | 5.89 | 7.06 | 9.42 | 11.77 | 14.13 | 17.66 | 23.55 | 29.44 |
| 200 | 7.85 | 9.42 | 12.56 | 15.70 | 18.84 | 23.55 | 31.40 | 39.25 |
A 100 × 10 flat is 1,000 mm², so 1,000 × 0.00785 = 7.85 kg/m. To convert any kg/m value to lb/ft, multiply by 0.67197.
Flat bar vs plate: what the callout is telling you
Drawings are inconsistent about what they call flat bar. You will see all of these for the same piece of steel:
- FB 3/8 x 3 or FLAT BAR 3/8" x 3"
- PL 3/8 x 3 (common on connection details even when the fabricator will cut it from bar stock)
- BAR 3 x 3/8 (width first, thickness second, which trips people up)
- 3/8" x 3" STRAP
The usual US convention is thickness first, then width, but not every detailer follows it. If a callout reads "3 x 3/8", nobody is making a bar 3 inches thick and 3/8 inch wide, so the order sorts itself out. The trouble is sizes like "1/2 x 3/4" where both readings are plausible. When in doubt, scale it off the detail. Our steel abbreviations and drawing symbols guide covers the other shorthand that shows up next to these callouts.
Whether you buy it as bar or cut it from plate is a purchasing decision, not a takeoff one. The weight is the same. What changes is the drop: a 4" wide piece cut from a 48" × 96" plate leaves you with offcuts you have to account for, while bar stock only drops at the ends. See waste factors in steel fabrication for how shops typically carry that.
Where flat bar hides in a takeoff
After enough takeoffs you start looking for flat bar in the same places every time:
- Stair and rail details. Stringer caps, tread support clips, baluster bottom rails, toe plates, and post base straps. The stairs and railings takeoff guide walks through a full flight.
- Embeds and bearing plates. Anything cast into concrete with headed studs welded on, plus loose bearing plates under lintels and beam ends.
- Connection material. Shear tabs are often 3/8" or 1/2" flat bar in 4" to 6" widths. They get counted once per connection, which on a big floor adds up quickly.
- Bracing and straps. Light X-bracing in pre-engineered buildings and mezzanines, hurricane straps, and kicker straps.
- Base and cap plate stock. Small column base plates are sometimes bar stock. Larger ones are plate; the base plate and anchor bolt takeoff guide covers those.
Most of this material is ordered to ASTM A36. If the spec calls out something else (A572 Gr 50 for heavier connection material, or stainless for exterior embeds), flag it, because the price per pound changes and the availability can change your lead time. Our steel grades guide covers the common ones.
Worked example: flat bar on one stair detail
Say a stair detail shows the following flat bar items for a single flight:
| Item | Size | Qty | Length each | Total length | lb/ft | Weight |
|---|---|---|---|---|---|---|
| Stringer cap | 3/8" × 2" | 2 | 14'-0" | 28.0 ft | 2.55 | 71.4 lb |
| Tread clip | 1/4" × 2" | 24 | 0'-6" | 12.0 ft | 1.70 | 20.4 lb |
| Post base strap | 1/2" × 4" | 6 | 0'-8" | 4.0 ft | 6.81 | 27.2 lb |
| Toe plate | 1/4" × 4" | 2 | 6'-0" | 12.0 ft | 3.40 | 40.8 lb |
That is about 160 lb of flat bar per flight before waste. It's small next to the stringers, but across ten flights it's most of a ton, and every one of those pieces has to be cut, drilled or punched, and welded. On misc metals the labor on small pieces is usually the bigger number, which is why the Division 5 metals estimating guide prices a lot of this per piece rather than per pound.
If the flat bar is going to be galvanized, add the zinc. The galvanizing cost per ton guide covers how galvanizers bill and what weight gain to expect.
Quick tips for flat bar takeoffs
- Count pieces, not just feet. A hundred 6-inch clips and 50 feet of continuous bar weigh the same, but they are very different jobs in the shop.
- Round up to stock lengths when buying. Takeoff weight is net. Purchase weight is sticks. Keep both columns.
- Watch the thickness fractions. 5/16" and 3/8" look almost identical on a scanned drawing. A misread changes weight by 20%.
- Don't forget the quantity multiplier on typical details. "TYP. AT ALL POSTS" on a railing detail can turn one strap into 80.
If your drawings are PDFs, Steelflo reads these sizes off the sheets and builds the takeoff so you're not transcribing every clip by hand. Take a look.
Frequently Asked Questions
How much does a 1/4 x 2 flat bar weigh per foot?
A 1/4" × 2" steel flat bar weighs about 1.70 lb per foot. It has a cross-section of 0.5 in², and 0.5 × 3.4028 = 1.70. A standard 20-foot bar weighs about 34 lb.
What is the formula for steel flat bar weight?
Weight in lb/ft equals width in inches times thickness in inches times 3.4028. The 3.4028 factor comes from steel at 490 lb/ft³: one square inch of section one foot long weighs 3.4028 lb. Many handbooks round it to 3.40.
Why do different flat bar charts show slightly different weights?
Most differences come from the density factor. Some tables use 3.40 lb per square inch of section per foot and others use 3.4028, which makes a gap of less than 0.1%. Actual bars also vary a little because of mill rolling tolerances.
Is flat bar the same as plate?
They are the same material, but flat bar is sold as narrow bar stock in fixed lengths (usually 20 feet), while plate is sold in wide sheets that you cut to size. Drawings often call flat bar "PL", so read the width to decide how it will actually be bought.
How do I convert flat bar weight from kg/m to lb/ft?
Multiply kg/m by 0.67197 to get lb/ft. For example, a 100 × 10 mm flat bar is 7.85 kg/m, which works out to about 5.27 lb/ft.