Steel Weight Calculator
Enter the shape, grade, and dimensions of your steel section to get the weight in kilograms, pounds, or tonnes. This calculator covers round bars, square bars, rectangular bars, flat bars, hexagonal bars, round tubes, square tubes, rectangular tubes, angle iron, and C-channel sections. Choose from nine common steel grades or enter a custom density. Results update as you type and a step-by-step panel shows every stage of the calculation.
How to calculate steel weight
Steel weight is the product of volume and density: Weight = Volume x Density. Volume equals the cross-section area of the profile multiplied by the length of the piece. Density depends on the steel grade: mild steel is typically 7870 kg/m3, while stainless steel 304 is 8000 kg/m3 because the alloying elements (chromium, nickel) are heavier than iron. For a round bar, the cross-section area is pi/4 x diameter squared. For hollow sections such as round tube or rectangular hollow section, you subtract the inner area from the outer area. For angle iron (L-section) the area is approximately thickness x (leg A + leg B - thickness). For a C-channel it is the web area plus two flange areas. Once you have the volume in cubic metres and the density in kg/m3, multiplying them gives the mass in kilograms.
Weight per metre and why it matters
Steel distributors and fabricators almost always quote bar and section products by weight per metre (kg/m), which is sometimes called linear mass density. This figure equals density x cross-section area and is independent of the length of any particular piece. Knowing the kg/m value lets you quickly estimate material cost, order quantities, and structural loads without measuring every piece. For example, a 25 mm diameter mild steel bar has a cross-section area of pi/4 x 0.025 squared = 0.000491 m2 and a linear density of 7870 x 0.000491 = 3.86 kg/m. A 6-metre bar of this size therefore weighs about 23.2 kg.
Choosing the right steel grade for your project
Grade selection affects both weight and cost. Mild steel (S235 or equivalent) is the cheapest option for general structural use and has a density around 7870 kg/m3. Stainless steels 304 and 316 are about 2 percent heavier than mild steel but resist corrosion in food-processing, chemical, and marine environments. Tool steels such as H13 and D2 are slightly lighter (7715 kg/m3) and are chosen for hardness and wear resistance rather than weight savings. Cast iron is notably lighter than wrought steel (7200 kg/m3) but is brittle under tensile load. If your alloy is not in the list, use the "custom density" option and enter the value from your material data sheet.
Manual-handling limits and safe lifting
Understanding piece weight is important for workplace safety. Most occupational health authorities recommend that individual manual lifts be kept below 25 kg where possible (with lower limits depending on lift position and frequency). Pieces above this threshold should be handled with a mechanical aid such as a hoist, crane, or forklift. For very large structural members that weigh several hundred kilograms, a crane with a rated capacity well above the piece weight is required. Total-order weights in the hundreds of tonnes are relevant for transport planning: a standard 20-foot shipping container holds about 22-25 tonnes of steel sections, and a road flatbed lorry is typically limited to 20-24 tonnes of payload depending on axle configuration and local regulations.
Steel grade densities
| Grade / type | Density (kg/m³) | Typical use |
|---|---|---|
| Mild steel (S235, A36) | 7870 | General structural, construction |
| Carbon steel (medium) | 7840 | Shafts, gears, fasteners |
| Cold-drawn steel | 7830 | Precision bars, turned parts |
| Stainless steel 304 | 8000 | Food, medical, marine |
| Stainless steel 316 | 8027 | Chemical plant, offshore |
| Stainless steel 410 (martensitic) | 7750 | Cutlery, valves, pumps |
| Tool steel (H13, D2 etc.) | 7715 | Dies, moulds, cutting tools |
| Wrought iron | 7750 | Heritage, decorative ironwork |
| Cast iron (grey) | 7200 | Housings, brake drums, pipes |
Standard densities used in structural and mechanical engineering calculations.
Frequently asked questions
What is the formula for steel weight?
Steel weight = cross-section area (m2) x length (m) x density (kg/m3). The cross-section area formula depends on the shape: for a round bar it is pi/4 x diameter squared; for a rectangular bar it is width x height; for a round tube it is pi/4 x (outside diameter squared minus inside diameter squared); and so on for other profiles. Density is typically 7850 to 8030 kg/m3 depending on the alloy, with mild steel at about 7870 kg/m3.
What density should I use for mild steel?
The most widely used value for mild steel (low-carbon steel such as S235, S275, A36) is 7850 to 7870 kg/m3. Structural engineering codes such as EN 1991 (Eurocode 1) specify 7850 kg/m3 as the nominal density for structural steel. This calculator uses 7870 kg/m3 for mild steel to match the common workshop reference, but the difference from 7850 is less than 0.3 percent and is negligible for most practical purposes.
Is stainless steel heavier than mild steel?
Yes, slightly. Stainless steels 304 and 316 are around 8000 to 8030 kg/m3, compared with 7870 kg/m3 for mild steel. The extra weight comes from the alloying elements: 304 contains about 18 percent chromium and 8 percent nickel, both denser than iron. For a given section size and length, a stainless piece is roughly 2 percent heavier than the same piece in mild steel.
How do I find the weight of a steel plate?
Select "Flat plate / sheet" as the shape, then enter the width, length, and thickness of the plate in your chosen unit. The calculator computes volume as width x length x thickness and multiplies by density. For example, a 1000 mm x 2000 mm x 10 mm mild-steel plate has a volume of 0.001 x 0.002 x 0.01 = 0.00002 m3 wait, sorry, that is 1 m x 2 m x 0.01 m = 0.02 m3, giving a weight of 0.02 x 7870 = 157 kg.
What is a square hollow section (SHS) and how is its weight calculated?
A square hollow section (SHS) is a tube with a square cross-section formed by hot-rolling or cold-forming steel strip. Its cross-section area is the outer square area minus the inner square area: (outside dimension)2 minus (outside dimension minus 2 x wall thickness)2. Multiply that area by the length and by the steel density to get the weight. SHS is widely used in structural frames, gates, and furniture because it has good torsional stiffness and a clean, uniform appearance.
How do I convert kg to pounds for a steel weight result?
Multiply kilograms by 2.20462 to get pounds (lb). Alternatively, select "Pounds (lb)" in the weight output unit selector and the calculator converts automatically. One metric tonne equals 1000 kg, and one short ton (US) equals about 907 kg (2000 lb), so be careful which tonne you are working in when dealing with large quantities.
Why does the calculator give weight per metre?
Weight per metre (kg/m), also called linear mass density, is the standard unit used by steel service centres and distributors when listing bar and section products in their catalogues. Knowing this value makes it easy to price a mixed order: multiply each line item length by the kg/m figure, sum the totals, and multiply by the price per kilogram or tonne. It is also useful for structural engineers who need to know the self-weight of a beam or column per unit length for load calculations.