Metal weight guide: how to calculate the weight of steel and aluminium

Metal weight is always the same calculation: volume multiplied by density. Carbon steel is taken at 7.85 g/cm3, austenitic stainless at 7.9 to 8.0 and aluminium at 2.70, which is why an aluminium part weighs roughly 0.344 times its steel equivalent. From that one rule come the standard shortcuts: 7.85 kg per square metre for every millimetre of steel sheet thickness, and 0.006165 multiplied by the diameter squared for round bar in kilograms per metre. Weight decides freight, lifting, foundations and the quantity on a purchase order, so getting it right before the material moves saves rework. This guide gives the densities, the formula for each form, and the cases where a calculated figure is not the figure that arrives.

Why calculated weight matters before the order

Metal is bought by the metre or the sheet but moved, lifted and charged by mass. A fabricator needs the weight to size a crane lift and a pallet, a structural engineer needs it as dead load in the design, and a trade buyer needs it to check a delivery note against what was ordered. The figures grow quickly: a single 2,000 x 1,000 mm steel plate at 10 mm thickness already weighs 157 kg, well beyond manual handling. Calculating the weight in advance also catches specification errors early: if a bill of materials comes out at twice the expected mass, either the section or the wall thickness is wrong. The arithmetic is simple enough to do on any quantity in a few minutes, and doing it before the order is placed is far cheaper than discovering the problem on a loading bay.

The single rule: volume multiplied by density

Every weight formula in this guide is the same statement rearranged: mass equals volume multiplied by density. The volume comes from the geometry of the form, the cross-sectional area multiplied by the length, and the density comes from the metal. All the coefficients that circulate in the trade, 0.00785, 0.006165, 0.02466, are simply that arithmetic pre-solved for a given shape in carbon steel, with the unit conversions folded in. Understanding this matters, because it means any coefficient can be rebuilt for a different metal by scaling it with the density ratio, and no separate table of aluminium or stainless coefficients has to be memorised or trusted.

Densities of the metals in the trade

Density is the one input that changes with the material rather than the shape. Carbon and structural steel is taken at 7.85 g/cm3, equivalent to 7,850 kg/m3, and this is the value the European standards themselves use: the masses tabulated in EN 10365 for I sections, H sections and channels were calculated on a density of 7,850 kg/m3. Stainless grades sit slightly higher because of their alloying content, and aluminium sits at roughly one third of steel.

For grade properties behind these figures see the guides to EN AW aluminium alloys and 304 and 316 stainless steel. Whether that one third weight saving justifies aluminium over steel depends on stiffness, welding and the load case, set out in our guide to aluminium versus steel.

Sheet and plate: weight per square metre

Flat product is the easiest case, because the area is known and only the thickness varies. For carbon steel, one square metre weighs 7.85 kg for every millimetre of thickness, so a 3 mm sheet weighs 23.55 kg/m2 and a 10 mm plate weighs 78.5 kg/m2. Multiply by the sheet area to get the piece weight: a 2,000 x 1,000 mm sheet at 3 mm therefore weighs 47.1 kg. The same logic gives 2.70 kg/m2 per millimetre in aluminium and 7.9 to 8.0 kg/m2 per millimetre in austenitic stainless. Applied to steel plate and sheet and aluminium sheet, this single figure covers most flat-product estimating.

Round bar

For round bar the cross-section is a circle, so the area is pi divided by four, multiplied by the diameter squared. Folded into the steel density, this gives the trade constant: weight in kg/m equals 0.006165 multiplied by the diameter in millimetres squared. A 10 mm steel round bar therefore weighs 0.6165 kg/m, a 20 mm bar weighs 2.466 kg/m, and the mass rises with the square of the diameter, which is why doubling a diameter quadruples the weight. In aluminium the same geometry gives 0.00212 multiplied by the diameter squared. The squared relationship is worth holding on to, because it explains why a small increase in specified diameter has a disproportionate effect on freight.

Square, flat and hexagon bar

Solid bars in other cross-sections follow the same pattern with a different area term. Square bar in steel is the side in millimetres squared, multiplied by 0.00785. Flat bar is the width multiplied by the thickness, both in millimetres, multiplied by 0.00785, so a 50 x 10 mm steel flat weighs 3.925 kg/m. Hexagon bar uses the across-flats dimension squared multiplied by 0.006798, the constant reflecting the hexagon area of the square root of three divided by two. The common factor 0.00785 is simply the steel density expressed for a cross-section in square millimetres and a length of one metre, which is why it reappears in every solid-bar formula.

Tube and pipe

A round tube is a ring in cross-section, and the standard trade form of the formula avoids calculating two circles. In carbon steel, weight in kg/m equals the outside diameter minus the wall thickness, multiplied by the wall thickness, multiplied by 0.02466, with all dimensions in millimetres. A 60.3 mm tube with a 3 mm wall therefore weighs 4.24 kg/m. For stainless the same expression is used with a constant scaled to the grade density, 0.02482 for 1.4301 and 0.02513 for 1.4404. The mean diameter term, the outside diameter minus the wall, is what makes the shortcut work, and it is also why wall thickness drives tube weight far more strongly than a small change in outside diameter.

Square and rectangular hollow sections

Hollow sections can be estimated as four walls: twice the wall thickness, multiplied by the sum of the two outside dimensions minus twice the wall thickness, multiplied by 0.00785 for steel. This treats the corners as square, so the result comes out slightly heavy, because a real hollow section has radiused corners that remove metal. For anything being ordered or designed, the nominal masses tabulated in the product standard are the figures to use rather than the estimate. Cold formed structural hollow sections are covered by EN 10219, and the guide to EN 10219 hollow sections sets out the grades and dimensional rules that go with those masses.

Rolled sections: read the standard, do not derive it

Beams, columns and channels are the one family where calculating from first principles is the wrong method. The cross-section includes tapered or parallel flanges, a web fillet and a root radius, and the root radius varies between mills, so a hand calculation will not reproduce the true area. EN 10365 tabulates the nominal dimensions and masses per metre for I sections, H sections and channels precisely so that designers and buyers work from one agreed figure, and those masses were derived at a density of 7,850 kg/m3. The rule is to take the mass per metre from the standard for the designated section, then multiply by length. Our guide to structural steel sections covers the section families themselves.

Aluminium: convert from the steel figure

Rather than keeping a second set of constants, the practical method for aluminium is to calculate in steel and scale the answer. The ratio of the densities, 2.70 divided by 7.85, is 0.344, so any steel weight becomes its aluminium equivalent when multiplied by 0.344. An aluminium part weighs about a third of the same part in steel, which is the reason aluminium dominates roof-mounted and hand-handled structures where dead load and manual handling govern. For 5000 series alloys at 2.66 the factor is 0.339, a difference small enough to ignore in freight estimating but worth carrying in a structural calculation. Extruded profiles follow the same rule through their cross-sectional area, as set out in the guide to aluminium profiles.

Stainless and galvanised corrections

Two corrections come up often enough to state plainly. For stainless, scale a carbon steel result by the density ratio: 7.9 divided by 7.85 for 1.4301, which adds under one per cent, and 8.0 divided by 7.85 for 1.4404, which adds about two per cent. Duplex 1.4462 at 7.8 comes out marginally lighter than carbon steel. For galvanised material the point is easy to get wrong. A Z275 coating carries 275 g/m2 of zinc counted over both surfaces together, but for continuously hot-dip coated flat product to EN 10346 the nominal thickness ordered already includes that coating. The zinc is less dense than steel, 7.14 against 7.85, so a coated sheet of a given nominal thickness weighs marginally less than the same nominal thickness of uncoated steel, not more. Taking 7.85 multiplied by the nominal thickness is therefore the right first approximation, sitting very slightly on the high side. The coating only adds weight on top when the thickness quoted is the base metal before galvanising. The galvanised steel DX51D guide covers the coating classes.

Theoretical weight against delivered weight

A calculated weight is a nominal figure, and the metal that arrives is manufactured to a tolerance around its nominal dimensions. Hot-rolled plate of 3 mm and above is supplied to the thickness tolerance classes of EN 10029, hot-rolled strip and sheet to EN 10051, hot-rolled aluminium plate from 2.5 mm to EN 485-3, cold-rolled aluminium sheet and strip to EN 485-4, extruded aluminium profiles to EN 755-9, and cold formed hollow sections to EN 10219-2. Within those tolerances a delivery can legitimately weigh a little more or less than the theoretical figure. This is normal and it is why weighbridge tickets rarely match a calculation exactly. Where the commercial basis matters, the contract should state whether the transaction is on theoretical or weighed mass.

Formula quick reference

Working out a delivery weight

Building up a consignment weight is the same calculation applied line by line. Take each item, find the mass per metre or per square metre for its form and grade, multiply by the quantity, and add the lines together. A useful discipline is to keep the grade with the line rather than converting at the end, because a mixed pallet scales by two different factors: 0.344 on the aluminium lines and 1.0 on the carbon steel ones. Add an allowance for packaging, timber bearers and banding, then check the total against the vehicle and the lifting equipment at the delivery point. Where a total approaches a handling limit, it is worth splitting the consignment at the order stage rather than at the gate.

Weight and specification support from ULAMEX

ULAMEX brings 38 years of experience in European steel and aluminium trading and has been in the metals wholesale industry since 1988, manufacturing its own structures under EN 1090-1 EXC2 and ISO 3834-2. Weights quoted against an enquiry are worked from the grade and the nominal dimensions of the material offered, with rolled sections taken from the standard masses rather than estimated.

Send the grades, forms, dimensions and quantities your project calls for, and ULAMEX will return a non-binding quotation with the calculated weight, lead time and availability, with a 3.1 inspection certificate available on request. See our steel and aluminium supply capabilities, the guide to EN 10204 material certificates, or contact the export desk at [email protected] or +48 504 424 761.

Frequently asked questions