30 9 月, 2026
Theoretical Weight vs Actual Weight on a Steel Order
Steel can be invoiced on theoretical weight — calculated from nominal dimensions — or on actual weight, measured on a weighbridge. The two are close but rarely identical, so the basis must be agreed in the order. The practical difference comes from dimensional tolerance.
How each basis works
| Basis | How it is determined | Effect on price |
|---|---|---|
| Theoretical weight | Calculated from nominal size and density | Price per tonne applied to a calculated tonnage; stable and easy to compare |
| Actual weight | Weighed at the mill or at the port | Price per tonne applied to the measured tonnage; reflects what actually ships |
Why they differ
Rolled products vary within the permitted dimensional tolerance. If the mill rolls on the heavy side of the tolerance, actual weight will exceed theoretical weight, and the reverse also happens. For a large order the difference can be material, which is why the basis is stated rather than assumed.
How to state it on the order
- Name the basis — theoretical or actual — explicitly in the contract
- State the dimensional tolerance standard that applies to the product
- Agree the weighing point and method if actual weight applies
- Show the basis on the invoice and the packing list so the documents agree
Related questions
See more answers in our Q&A and our steel knowledge base.
Frequently asked questions
What is the difference between theoretical and actual weight for steel?
Theoretical weight is calculated from nominal dimensions; actual weight is measured. They differ because rolled products vary within dimensional tolerance, so the basis changes what you pay on a per-tonne price.
Which weight basis is better for buyers?
Neither is inherently better. Theoretical weight gives a stable, comparable figure; actual weight reflects what physically ships. What matters is that the basis is stated in the order and used consistently in the documents.
How is theoretical weight calculated?
From the nominal dimensions and the density of steel. For a round pipe it is (D – t) x t x 0.02466 kg/m; for plate it is thickness x 7.85 kg/m2; and there are standard formulas for the other shapes. Our weight calculator applies them.
Still have a question about your order? Send the specification, quantity and destination port and we will answer it with the quotation. See our quality and inspection process, the product catalogue, or request a quotation.