Steel plate weighs 40.8 pounds per square foot for every inch of thickness. A 1/4" plate is 10.2 psf, a 1/2" plate is 20.4 psf, and a 1" plate is 40.8 psf — multiply by the area in square feet and you have the weight. For plate priced as bar (a width and a running length), use the 3.4028 rule instead: width (in) × thickness (in) × 3.4028 = pounds per foot.
Both numbers come from the same place: structural steel at 490 lb/ft³. Everything on this page is that one density, sliced different ways.
Steel plate weight chart by thickness
Weights per square foot for the thicknesses you actually see on structural drawings, plus the weight of a full 4' × 8' sheet at each thickness — useful for sanity-checking a mill order or figuring out whether two guys can carry it (short answer past 3/16": no).
| Thickness | Weight (psf) | 4' × 8' sheet (lb) |
|---|---|---|
| 3/16" | 7.65 | 245 |
| 1/4" | 10.2 | 326 |
| 5/16" | 12.75 | 408 |
| 3/8" | 15.3 | 490 |
| 7/16" | 17.85 | 571 |
| 1/2" | 20.4 | 653 |
| 5/8" | 25.5 | 816 |
| 3/4" | 30.6 | 979 |
| 7/8" | 35.7 | 1,142 |
| 1" | 40.8 | 1,306 |
| 1-1/4" | 51.0 | 1,632 |
| 1-1/2" | 61.2 | 1,958 |
| 2" | 81.6 | 2,611 |
For plate detailed as bar stock — a thickness and a width, cut to length — here are the running weights in lb/ft for common PL callouts. These match the AISC-style catalog values (PL 1/2 × 10 = 17.0 lb/ft, exactly what 0.5 × 10 × 3.4028 gives you):
| Thickness | 4" wide | 6" wide | 8" wide | 10" wide | 12" wide |
|---|---|---|---|---|---|
| 1/4" | 3.4 | 5.1 | 6.8 | 8.5 | 10.2 |
| 3/8" | 5.1 | 7.65 | 10.2 | 12.75 | 15.3 |
| 1/2" | 6.8 | 10.2 | 13.6 | 17.0 | 20.4 |
| 3/4" | 10.2 | 15.3 | 20.4 | 25.5 | 30.6 |
| 1" | 13.6 | 20.4 | 27.2 | 34.0 | 40.8 |
Notice the pattern: every value in that table is just thickness × width × 3.4028. You don't need to memorize the table — you need to memorize the rule.
What is the formula for steel plate weight?
Weight = volume × density. For structural steel, density is 490 lb/ft³ (0.2836 lb/in³), and there are two working forms of the formula depending on how the plate is dimensioned.
Per square foot (plate and sheet):
Weight (psf) = thickness (in) × 40.8
The 40.8 is 490 lb/ft³ ÷ 12, i.e., the weight of a 1-foot-square slab one inch thick. This is the fastest form for base plates, embed plates, and anything called out as thickness × plan dimensions.
Per running foot (bar and flat stock):
Weight (lb/ft) = thickness (in) × width (in) × 3.4028
The 3.4028 is 490 ÷ 144 — the weight of one cubic foot spread over 144 in² of cross-section. It works for any cross-sectional area, not just rectangles, which is why it's the standard sanity check for fabricated and built-up sections: take the area in square inches, multiply by 3.4028, and you have lb/ft. A W12X26 has an area of 7.65 in²; 7.65 × 3.4028 = 26.0. The designation checks itself. That same first-principles check is how we audit our own section database — if a catalog weight and the physics disagree by more than a couple percent, one of them is wrong.
For rolled shapes the weight is already baked into the name, so you rarely compute it — see how to calculate steel beam weight for the shape side of this. Plate is the one category where you compute weight from scratch on every job, because plates come in whatever dimensions the connection needed.
One caveat: 490 lb/ft³ is the AISC convention for carbon and low-alloy structural steel. Stainless runs about 501, aluminum about 169. If the drawing says A36, A572, or A588, use 490 and don't overthink it.
How much does a 1/2 inch steel plate weigh per square foot?
A 1/2" steel plate weighs 20.4 pounds per square foot. That's 0.5 × 40.8, and it makes 1/2" plate a convenient mental anchor: roughly 20 psf, so a 2' × 2' base plate is about 82 lb and a 4' × 8' sheet is about 650 lb.
Scaling from the anchor is faster than re-deriving: 1/4" is half of that (10.2 psf), 1" is double (40.8 psf), 3/4" is one and a half times (30.6 psf). If you hold one number in your head from this article, hold 20.4.
Metric plate weights: kg/m² by thickness
Same physics, metric density: 7,850 kg/m³, which works out to 7.85 kg/m² per millimeter of thickness. So the formula is simply thickness (mm) × 7.85.
| Thickness (mm) | Weight (kg/m²) | Nearest imperial | Weight (psf) |
|---|---|---|---|
| 6 | 47.1 | 1/4" | 10.2 |
| 8 | 62.8 | 5/16" | 12.75 |
| 10 | 78.5 | 3/8" | 15.3 |
| 12 | 94.2 | 1/2" | 20.4 |
| 16 | 125.6 | 5/8" | 25.5 |
| 20 | 157.0 | 3/4" | 30.6 |
| 25 | 196.3 | 1" | 40.8 |
The imperial "equivalents" are nominal — 12 mm is 0.472", not 0.500" — so don't substitute one for the other on anything with a design check. But for weighing a plate list off a European or Australian drawing, thickness × 7.85 gets you kg/m², and kg/m² × 0.2048 converts to psf if your pricing is imperial.
Plate takeoff tips: base plates, stiffeners, gussets, cap plates
Plates are where takeoffs bleed accuracy, because they're small, numerous, and scattered across detail sheets instead of listed in a schedule. Some field-tested habits:
- Base plates: live on column details and the anchor bolt plan, usually one per column. Cross-check the count against the column count — if you have 22 columns and 19 base plates, go find the other three. The full workflow, including anchor bolts and leveling, is in the base plate and anchor bolt takeoff guide.
- Stiffeners: almost always come in pairs (both sides of the web), and moment connections often take two pairs. When a detail says "PL 3/8 × 4 stiffener," the piece count is 2 or 4 per connection, not 1. Multiply by the number of times that detail is referenced on the plans — this is the single most common plate undercount.
- Gussets: one per brace end, so count brace ends, not braces. A 40-brace building has 80 gusset locations. Gussets are also irregular — take off the bounding rectangle and eat the scrap, because that's what the shop will burn from anyway.
- Cap plates: one per column top at joist and beam bearing conditions. Easy to skip because they hide on the same detail as the base plate and nobody reads to the top of the column.
- Round up thickness on price, never down on weight. Suppliers stock standard gauges; a 7/16" callout may get filled with 1/2" material. Weigh what you'll buy.
Why plates get missed in takeoffs — and what it costs
Plates get missed because they don't live where the tonnage lives. Beams and columns sit in framing plans and schedules; plates sit in connection details, typical details that apply "U.N.O." across forty locations, and general notes. A manual takeoff that walks the framing plans and stops will capture 95% of the tonnage and maybe 60% of the piece count — and the missing pieces are all labor-dense.
That's the real cost. On a typical job, connection material is 8–12% of the steel weight but a much larger share of the shop hours: every stiffener is a fit-and-weld, every gusset gets beveled, every base plate gets drilled or burned for anchor bolts. Miss 300 lb of stiffeners and you've missed maybe $250 of material and 20 hours of shop time. Estimators who bid plate off a weight allowance ("add 10% for connections") get away with it on beam-and-girder work and get hurt on braced frames and moment frames, where connection material can run past 15%.
This is also where detection software earns its keep or doesn't. SteelFlo boxes every plate callout it finds on every sheet — details, sections, and notes included, with 95-99% accuracy once you've verified the flagged items — so the plate list comes from the drawings rather than from an allowance. The count is the number of boxes you can see and check, which matters more for plates than for anything else on the job, precisely because plates are the pieces nobody double-checks. Rolled shapes get validated against a section database (here's how that works for AISC shapes); plates get validated by you, looking at a box on a detail sheet.
Worked example: weighing the plate list from one detail sheet
Here's a plate list pulled from a single column-and-brace detail sheet on a small industrial job, weighed with nothing but the two formulas above. Weight each piece as thickness × width × length × 0.2836 (lb/in³), or use the lb/ft table for the running items.
| Item | Callout | Qty | Weight each (lb) | Total (lb) |
|---|---|---|---|---|
| Base plates | PL 3/4 × 12 × 1'-2" | 8 | 35.7 | 286 |
| Stiffeners | PL 3/8 × 4 × 0'-8" | 24 | 3.4 | 82 |
| Gussets | PL 1/2 × 6 × 0'-9" | 12 | 7.7 | 92 |
| Cap plates | PL 1/2 × 8 × 0'-8" | 6 | 9.1 | 54 |
| Total | 50 | 514 |
Checking one line: the base plate is 0.75 × 12 × 14 = 126 in³, times 0.2836 = 35.7 lb. Or per square foot: 12" × 14" is 1.17 ft², times 30.6 psf = 35.7 lb. Same answer, pick whichever form matches how the plate is called out.
Now the estimating punchline: 514 lb is about a quarter ton of steel — maybe $200 of material — but it's 50 pieces, each one a layout, a cut, a fit, and a weld. At even 20 minutes of shop time per piece, that's 16+ hours riding on one detail sheet. Weigh the plates, but count them first. The weight prices the material; the count prices the job.
Want the math done for you? The free steel weight calculator handles plate, bar, and all the rolled shapes — 4,500+ sections across 6 international standards — with no signup. And if you'd rather have every plate callout on the drawings found and boxed automatically, SteelFlo's first 3 takeoffs are free.