What this calculator does
This steel calculator works out how heavy a round steel bar or rod is, given its diameter, length and density. It is the calculation behind a mill weight chart or a supplier order sheet: find the cross-section area from the diameter, multiply by length to get volume, then multiply by density to get mass.
The steel formula is the same one used for any solid cylinder, but steel bar tables usually skip straight to a weight-per-metre figure for each standard diameter. Building it from the diameter up here means it also works for odd sizes, other round-section metals, or a quick check against a supplier quote.
The formula
The bar is treated as a cylinder. Cross-section area comes from the diameter using area = (π ÷ 4) × diameter², then that area is multiplied by the bar length to get volume, and volume is multiplied by density to get weight. Density defaults to 7,850 kg/m³ for mild steel but can be edited for stainless, aluminium or any other round-section metal.
| Term | Meaning |
|---|---|
| Diameter | The bar diameter, measured straight across the round cross-section. |
| Density | Mass per unit volume of the metal; mild steel is about 7,850 kg/m³. |
| Weight per metre | The bar weight divided by its length, the figure most mill charts quote directly. |
The inputs explained
| Field | What to enter |
|---|---|
| Bar diameter (mm) | The bar diameter in millimetres, as stamped on the mill certificate or measured with callipers. |
| Bar length (m) | The total length of the bar or rod being weighed. |
| Density (steel ≈ 7850 kg/m³, edit for other metals) (kg/m³) | Density of the metal. Leave at 7,850 kg/m³ for ordinary mild steel, or change it for another material. |
When to use it
Ordering by weight instead of length
Steel suppliers often price and freight by weight rather than length, so converting a cutting list of bar lengths into a total weight gives a figure that matches the invoice.
Checking a delivery against the order
Weighing a bundle on arrival and comparing it to the expected weight for its stated diameter and length is a quick check that the right grade or size was actually delivered.
Estimating load before lifting or transport
Knowing the weight of a bar or a bundle of bars in advance matters for choosing lifting gear, a vehicle load limit, or how many bars a person can safely carry at once.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does a 6 m steel bar weigh at different diameters?
Common round bar diameters, all cut to a 6 m length.
| Diameter | Weight | Weight per metre |
|---|---|---|
| 8 mm | 2.37 kg | 0.395 kg/m |
| 10 mm | 3.70 kg | 0.617 kg/m |
| 12 mm | 5.33 kg | 0.888 kg/m |
| 16 mm | 9.47 kg | 1.578 kg/m |
| 20 mm | 14.80 kg | 2.466 kg/m |
| 25 mm | 23.12 kg | 3.853 kg/m |
How does length change the weight of a 16 mm bar?
A single 16 mm bar cut to a range of lengths.
| Bar length | Weight | Weight per metre |
|---|---|---|
| 1 m | 1.58 kg | 1.578 kg/m |
| 2 m | 3.16 kg | 1.578 kg/m |
| 3 m | 4.74 kg | 1.578 kg/m |
| 6 m | 9.47 kg | 1.578 kg/m |
| 9 m | 14.21 kg | 1.578 kg/m |
| 12 m | 18.94 kg | 1.578 kg/m |
Questions
What density should I use for steel?
Mild steel is commonly taken as 7,850 kg/m³, which is the default here. Stainless steel is slightly higher, at around 7,900 to 8,000 kg/m³ depending on the grade, and other metals such as aluminium are considerably lighter, so the density field can be edited to match whatever material is actually being weighed.
Does this work for square or rectangular bar?
No, this steel formula assumes a round cross-section. A flat or square bar has a different cross-section area, so a plate or rectangular-section calculation is needed instead; see the steel plate weight calculator for flat stock.
Why does my supplier quote a slightly different weight?
Mill tolerances mean actual bar diameter can vary a little from the nominal size, and some suppliers round their published weight-per-metre figures. Small differences of a percent or two against a supplier chart are normal and not a sign of an error.
How do I work out the weight of a bundle of bars?
Calculate the weight of one bar at the given diameter and length, then multiply by the number of bars in the bundle, since weight scales linearly with the number of identical bars.
For flat or rectangular steel stock rather than round bar, see the steel plate weight calculator. For working out how much bar a concrete slab needs in the first place, see the rebar for a concrete slab calculator.