How do you calculate the weight of a round bar?
Round bar weight is π/4 × diameter² × length × density. For carbon steel with the diameter in millimetres, the shortcut is diameter² × 0.006165 kg per metre; for 304 stainless the constant is about 0.00623.
Key Takeaways
- The formula is π/4 × D² × length × density, with no bore to subtract.
- Carbon steel shortcut: D² × 0.006165 kg per metre, with D in millimetres.
- Stainless 304 shortcut: D² × 0.00623 kg per metre.
- Weight rises with the square of diameter — doubling the diameter quadruples the weight per metre.
- A 50 mm carbon steel bar weighs about 15.4 kg per metre; the same bar in titanium Grade 2 weighs about 8.9 kg per metre.
- Bar is normally supplied in 3 to 6 metre random lengths unless a cut length is specified.
The formula and the shortcut
A round bar is a solid cylinder, so there is no bore to subtract and the calculation is the simplest of the three. Volume per metre is π/4 × D² × 1000 cubic millimetres, with D in millimetres.
Collapsing the constants gives the working shortcut for carbon steel: kg per metre = D² × 0.006165. For 304 stainless use 0.00623, for 316 use 0.00628, and for titanium Grade 2 use 0.00354.
Worked example. A 50 mm carbon steel bar: 50² × 0.006165 = 15.4 kg per metre, so a 6 metre bar weighs about 92 kg.
Why bar weight matters at quotation stage
Bar is bought by weight and machined into a component, so the buyer pays for material that ends up as swarf. On an exotic grade the difference between a 55 mm and a 60 mm starting bar is not trivial: at Inconel 625 density that step adds roughly 2.4 kg per metre of stock, all of which is removed and paid for.
Calculating the bar weight before ordering therefore does two things — it validates the freight estimate, and it shows whether stepping down one size still leaves enough machining allowance. Send the finished component drawing and we will confirm the bar size the part can actually be cut from.
Frequently Asked Questions
About 15.4 kg per metre in carbon steel, calculated as 50 squared times 0.006165. In 304 stainless the same bar is about 15.6 kg per metre.
Square the diameter in millimetres and multiply by 0.006165 for carbon steel, or 0.00623 for 304 stainless, to get kilograms per metre.
Yes. Bar is normally supplied in 3 to 6 metre random lengths, and cut-to-length service is available on request so the buyer does not pay to freight offcuts.
Carbon and mild steel, stainless 304 and 316, duplex and super duplex, alloy steel, nickel alloys including Inconel, Monel and Hastelloy, titanium, copper alloys and aluminium.