BUYING GUIDE
Theoretical weight
Theoretical weight is the weight of a piece of metal calculated from its dimensions and the standard density of its alloy — steel plate at 7.85 g/cm³, for example. The metal trade prices on theoretical weight, not weighbridge readings, because it is repeatable, checkable by anyone with the dimensions, and immune to scale disputes. Every 2ndMetal listing shows it.
The arithmetic
For flat product the formula is length × width × thickness × density. A carbon steel plate of 2,000 × 1,000 × 10 mm works out at 0.02 m³ × 7,850 kg/m³ = 157 kg. Stainless runs slightly heavier per volume, aluminium at roughly a third of steel.
For pipe, weight follows from outside diameter and wall thickness — the standard kg/m figures published for each pipe size and schedule. For rolled sections — beams, channels, angles — each designation has a published kg/m from the section tables: an IPE 200 is 22.4 kg/m wherever it was rolled.
Why not just weigh it?
Weighbridge readings vary with the scale, the calibration, the mud on the truck and who is reading the display. Theoretical weight is the same number for everyone: state the dimensions and the alloy, and buyer and seller can each do the arithmetic and land on the same kilograms.
Mill tolerance means a real piece can weigh a little more or less than theory — plate is rolled to a thickness tolerance, and mills tend to run it slightly heavy. The trade accepts this: theoretical weight is the commercial quantity, and the small physical variance is priced into the market.
What it means when buying surplus
On 2ndMetal, every listing's weight is calculated from its measured dimensions and the alloy's standard density — the same tables everyone in the trade uses. No weighbridge figure ever enters the price.
This protects buyers in a specific way: you can verify what you're paying for from the listing alone. Take the dimensions on the page, run the arithmetic, and the kilograms either check out or they don't — before any money moves.
Common questions
What density figures are used?
The standard trade figures per alloy family — carbon and low-alloy steel at 7.85, stainless austenitics slightly above it, aluminium around 2.70, copper 8.94, titanium 4.51 (all g/cm³). The listing's family determines the density applied.
What if the delivered piece weighs slightly differently?
It usually will, within mill tolerance — that is normal and expected. The commercial quantity is the theoretical weight stated on the listing, which is what you agreed to and what the documents show.
How is weight calculated for beams and channels?
From published section tables: each designation carries a standard kg/m, multiplied by the piece's length. Where a section is non-standard, the listing says so and the weight is derived from its actual cross-section.