Formula
Weight is volume times density. Volume is computed in cubic inches, converted with (0.0254 m)³, and multiplied by the alloy’s kg/m³. Pounds use 0.45359237 kg/lb, so a 12 × 12 × 1 inch carbon-steel plate at 7850 kg/m³ is 40.84 lb.
plate = L × W × t
round bar = π/4 × d² × L
round tube = π/4 × (OD² − ID²) × L
angle = t × (leg A + leg B − t) × L
channel = [d × tw + 2 × tf × (bf − tw)] × L
W-shape = [2 × bf × tf + tw × (d − 2 × tf)] × L
A wall thicker than half the outside size is clamped so the inside cannot go negative. Rectangular tube uses the same idea: the hollow is (width − 2t) by (height − 2t), and a vanished hollow is a solid bar. These are net sections. They ignore fillets and the designation weight of a rolled shape. The speeds and feeds calculator is the next step if the piece is going on a machine.
Worked examples
12 × 12 × 1 in carbon steel. 144 in³ at 7850 kg/m³ is 40.84 lb, 18.52 kg.
1 in round bar, 36 in long, same steel. π/4 × 36 = 28.27 in³, which is 8.02 lb.
The same plate in 6061. Density drops from 7850 to 2700, so the weight drops by 2700/7850.
Reference
Room-temperature densities used on this page. Grade 2 titanium is not Ti-6Al-4V, and the brass figure is generic, not C360.
| Alloy | kg/m³ | 12 × 12 × 1 in |
|---|---|---|
| Carbon / mild steel | 7850 | 40.84 lb |
| Stainless 304 | 8000 | 41.62 lb |
| Aluminum 6061 | 2700 | 14.05 lb |
| Brass, generic | 8500 | 44.22 lb |
| Copper | 8960 | 46.61 lb |
| Titanium Grade 2 | 4510 | 23.46 lb |
Questions
Where do the densities come from?
They are room-temperature typical values: 7850 kg/m³ for carbon steel, 8000 for 304 stainless, 2700 for 6061 aluminum, 8500 for generic brass, 8960 for copper, and 4510 for Grade 2 titanium. A mill certificate replaces the table.
Is a W-shape the handbook weight?
No. The W-shape here is two flanges plus the web between them, from the depth, flange width, flange thickness, and web thickness you type. A published weight per foot for a W8×31 or any other designation wins.
Why is a 12 inch square of 1 inch plate not exactly 40.8 lb from 490 lb/ft³?
This page multiplies cubic inches by 7850 kg/m³ and converts with 0.45359237 kg/lb. That plate is 40.84 lb. A 490 lb/ft³ rule of thumb is close, and the certificate is closer than either.
Sources
- Densities are typical room-temperature values of the kind published in ASM and engineering references: carbon steel 7850, 304 stainless 8000, 6061 aluminum 2700, copper 8960, Grade 2 titanium 4510 kg/m³. Brass at 8500 is a generic figure, not a specific UNS alloy. The mill certificate wins.
- Mass conversion: 1 lb = 0.45359237 kg. One inch = 0.0254 m exactly.