Metal Weight Calculator

Weight (kg) = length (ft) × width (ft) × thickness (in) ÷ 12 × 0.0283168 m³ per ft³ × density (kg per m³)

L

Length of the piece in feet — the page converts whatever unit you pick into feet first

W

Width of the piece in feet

T

Thickness in inches: plate and sheet are quoted in inches (or in millimetres, if you switch the unit)

÷ 12

Inches in a foot, needed because two of the three dimensions are in feet and the third is in inches

0.0283168

Cubic metres in a cubic foot — the step that puts the volume into the unit the density is quoted in

ρ

Density of the alloy: 7,850 kg per m³ steel, 7,930 stainless, 2,700 aluminium, 8,960 copper, 8,500 brass, 7,200 cast iron

Use it to price a lift, to check a trailer or a pallet, to work out freight, or to find out whether a piece is a two person job. It is also the page for comparing alloys: the same dimensions in steel, aluminium and copper differ by more than three times, so if weight is the constraint, the check takes a few seconds. If what you are weighing is a round bar, a pipe or a tube, the shape here does not apply — the FAQ below gives the two extra factors that turn a diameter into an area. For the weight of a casting or a forging at a stated density, the same three dimensions work as long as the piece really is a rectangular prism; anything with a taper, a rib or a hole weighs less than this returns.

1. A 4 × 8 ft steel sheet, half an inch thick — the page's default

   1. Thickness in feet: 0.5 ÷ 12 = 0.041667 ft
   2. Volume: 8 × 4 × 0.041667 = 1.3333 ft³
   3. Into cubic metres: 1.3333 × 0.0283168 = 0.037756 m³
   4. Weight: 0.037756 × 7,850 = 296.38 kg
   5. In pounds: 296.38 × 2.20462 = 653.4 lb; in tonnes: 0.296

   296 kilograms is the figure that decides how the sheet moves: too heavy for one person to handle safely, so it needs two or a small lift, and it is the number a freight quote is built on. A 4 × 8 sheet is the standard mill size in North America, which is why it is the default here — most stock you buy in a yard started out as one of these, cut down. Half an inch is a structural plate rather than a sheet: sheet metal proper is below about an eighth of an inch, and the page handles that too, just with a much smaller answer.

2. The same sheet in aluminium

   1. Volume: unchanged at 1.3333 ft³, because only the alloy moved
   2. Into cubic metres: 1.3333 × 0.0283168 = 0.037756 m³
   3. Weight: 0.037756 × 2,700 = 101.94 kg
   4. In pounds: 101.94 × 2.20462 = 224.7 lb; in tonnes: 0.102

   Aluminium is 2,700 kilograms per cubic metre against steel's 7,850, so the same sheet is a little over a third of the weight and one person can move it. That ratio — not any difference in strength per unit weight — is the everyday reason to choose it, and it is the reason this page exists as a calculator rather than a table: the answer moves by more than three times on a single dropdown. Copper is the reverse case at 8,960, so a copper sheet this size would be 338 kilograms, more than the steel.

3. A 20 × 10 ft cast iron plate, two inches thick

   1. Thickness in feet: 2 ÷ 12 = 0.16667 ft
   2. Volume: 20 × 10 × 0.16667 = 33.333 ft³
   3. Into cubic metres: 33.333 × 0.0283168 = 0.94389 m³
   4. Weight: 0.94389 × 7,200 = 6,796 kg
   5. In pounds: 6,796 × 2.20462 = 14,982.7 lb; in tonnes: 6.796

   Nearly seven tonnes is a crane job and a flatbed, not a delivery van, and this is the case where the tonnes output stops being decoration: 6.796 tonnes is the number that goes on the lifting plan. It is also worth noticing that cast iron, at 7,200, is the lightest thing on the list apart from aluminium — the name suggests something heavier than steel, and it is not. The other thing to watch on a piece this size is that the density of cast iron varies more than the wrought alloys do, so 7,200 is the middle of a band rather than a specification.

The page covers rectangular sections only — plate, sheet, flat bar, square bar and strip. Round bar, pipe, tube, angle, channel, beam and any other profile are outside it, and the reason is a rendering constraint rather than a judgement about what matters: the calculator has no way to show a field only for some shapes, so a shape selector would leave a width box on screen that a round bar ignores. The FAQ below gives the extra factor for a round bar, which is the most common of the missing cases. The densities are handbook figures for wrought alloys and one cast iron rather than values certified for your heat: stainless moves with the grade, brass moves with the copper content, and the aluminium alloys most people buy are close enough to 2,700 that the difference rarely shows. A piece with a taper, a rib, a hole or a machined recess weighs less than a solid prism of the same envelope, and this page has no way to subtract any of that. Finally, the result is a mass, not a load rating: what a piece weighs and what a structure can carry are different questions, and nothing here is a substitute for a section capacity check.

How much does a 4 × 8 sheet of steel weigh?

296 kilograms at half an inch thick, which is the default on the page. Steel is 7,850 kilograms per cubic metre and the sheet is 1.3333 cubic feet, or 0.037756 cubic metres. Thickness scales the answer directly: a quarter inch sheet is 148 kilograms, an eighth is 74, and a one inch plate is 593. The same sheet in aluminium is 102 kilograms, which is the comparison this page is most often opened for.

What is the weight of a round bar?

Multiply the square of the diameter by 0.00617 kilograms per metre per square millimetre, so a 25 mm bar is 0.00617 × 625 = 3.86 kilograms per metre. The general form is π ÷ 4 × d² × density, which is exactly the same calculation as this page for a section whose area is π d² ÷ 4 rather than width times thickness. The page itself covers rectangular sections only, so use that formula for round bar, and subtract the bore for a tube: π ÷ 4 × (D² − d²) × density.

How much does aluminium weigh compared with steel?

About a third as much: 2,700 kilograms per cubic metre against 7,850 — the metal is spelled aluminium here and aluminum in the US, and it is the same 2,700 either way. That is the density ratio alone and says nothing about strength, which is a separate question — a part redesigned in aluminium is rarely a straight substitution, because the alloy usually has to be thicker to carry the same load. Among the six metals here, copper at 8,960 is the heaviest, brass at 8,500 is close behind, and cast iron at 7,200 is the lightest apart from aluminium.

How do I work out pounds per square foot per inch?

Divide the density in pounds per cubic foot by 12 — for steel, 490 ÷ 12 = 40.8 pounds per square foot per inch of thickness. That is the figure at the top of a US steel weight table, and it is the quickest way to check any steel plate: area in square feet times thickness in inches times 40.8 gives pounds. In metric the same shortcut is 7.85 kilograms per square metre per millimetre, which is the 7.85 in every Chinese steel handbook, and it comes from the same 7,850 density divided by 1,000.

Why is there no shape selector?

Because the calculator cannot hide a field. Every input on the page is shown at once, so a shape dropdown would leave a width box on screen for a round bar and a diameter box for a plate, and whichever one did not apply would be silently ignored — the worst kind of wrong answer, because the page looks fine. Restricting the page to rectangular sections keeps every field meaningful for every piece it accepts. Round bar and tube are covered by the formula in the FAQ above.

How accurate is the weight?

Within a percent or so for stock that really is a rectangular prism, which is the point of a nominal density. Mill tolerances on thickness are the larger error in practice: plate is rolled to a thickness tolerance of a few percent, and a sheet at the top of that tolerance weighs more than the nominal figure. Alloy substitution shifts the density — a 304 and a 316 stainless differ slightly, and brass moves with its copper content — so if a weight has to be certified, take the density from the mill certificate rather than from this table.

• Approximate Conversions from U.S. Customary Measures to Metric — the chart behind the pound, the short ton and the cubic foot figures used here — National Institute of Standards and Technology
• The International System of Units (SI) brochure — the kilogram and the tonne, the two mass units the results are reported in — Bureau International des Poids et Mesures (BIPM)