What this calculator does
A steel plate's weight comes down to one formula: length times width times thickness gives its volume, and volume times density gives its weight. Mild steel has a density of about 7,850 kg per cubic metre, which is the figure most steel weight calculators default to, but the same formula works for any flat metal plate once the right density is entered.
This calculator takes a plate's length, width and thickness, converts them to a volume, and multiplies by a density figure you can edit, defaulting to standard mild steel. Because density is an open field rather than a fixed constant, the same calculator handles stainless steel, aluminium, brass or any other flat plate material, not just mild steel.
The formula
The plate's volume is length times width times thickness, each converted to metres so the result comes out in cubic metres. Multiplying that volume by the density, in kilograms per cubic metre, gives the weight in kilograms. Because density varies by material and even by alloy, it is entered as its own field rather than hard-coded to one steel grade.
| Term | Meaning |
|---|---|
| Density | Mass per unit volume of the material, in kg/m³; mild steel is about 7,850 kg/m³, but this varies by alloy and material. |
| Volume | Length × width × thickness, the space the plate occupies, here converted to cubic metres. |
| Plate area | Length × width, the flat face area of the plate, shown separately from its volume. |
The inputs explained
| Field | What to enter |
|---|---|
| Length (mm) | The length of the plate. |
| Width (mm) | The width of the plate. |
| Thickness (mm) | The thickness of the plate; this is usually the smallest of the three dimensions. |
| Density (steel ≈ 7850 kg/m³, edit for other metals) (kg/m³) | The material density in kg/m³. Leave at 7,850 for standard mild steel, or change it for stainless steel, aluminium or another material. |
When to use it
Estimating a plate's weight before delivery
Freight and lifting equipment both have weight limits, so working out a plate's weight from its dimensions before it arrives avoids a surprise on delivery day.
Costing a fabrication job
Steel is commonly priced by weight, so converting a plate's dimensions into a weight figure is often the first step in pricing a cut piece before any labour is added.
Comparing materials for the same part
Swapping the density figure between steel, aluminium and stainless steel on the same dimensions shows how much weight (or cost) changes with the material choice, without re-deriving the geometry each time.
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 does plate weight change with thickness?
A fixed 1,000 mm by 500 mm plate, across a range of thicknesses.
| Thickness | Weight | In pounds |
|---|---|---|
| 3 mm | 11.78 kg | 25.96 lb |
| 5 mm | 19.63 kg | 43.27 lb |
| 8 mm | 31.40 kg | 69.23 lb |
| 10 mm | 39.25 kg | 86.53 lb |
| 16 mm | 62.80 kg | 138.45 lb |
| 20 mm | 78.50 kg | 173.06 lb |
How does the same plate weigh in different materials?
A fixed plate size, across a range of material densities.
| Material density | Weight | In pounds |
|---|---|---|
| 2700 kg/m³ | 13.50 kg | 29.76 lb |
| 4500 kg/m³ | 22.50 kg | 49.60 lb |
| 7200 kg/m³ | 36.00 kg | 79.37 lb |
| 7850 kg/m³ | 39.25 kg | 86.53 lb |
| 8000 kg/m³ | 40.00 kg | 88.18 lb |
| 8960 kg/m³ | 44.80 kg | 98.77 lb |
Questions
What density should I use for mild steel?
About 7,850 kg/m³ is the standard figure used across the steel industry for mild and structural steel, which is why it is the default here. Specific alloys and steel grades can vary slightly either side of that figure.
Does this work for materials other than steel?
Yes. Because density is an editable field, entering a different figure, such as roughly 2,700 kg/m³ for aluminium, 8,960 kg/m³ for copper or 8,000 kg/m³ for stainless steel, gives the correct weight for that material using the same length, width and thickness inputs.
Why is the weight so different for a small change in thickness?
Weight scales directly with thickness because volume is proportional to it: doubling the thickness of a plate exactly doubles its volume and therefore its weight, with the length and width unchanged.
What if I need the weight of a round bar or rod instead of a flat plate?
This calculator is built specifically for flat rectangular plates. For round bars, rods or a mix of shapes and materials, the metal bar and sheet weight calculator handles both rectangular and round profiles with a set of common material presets.
For round bars, rods and a choice of preset metals, see the metal bar and sheet weight calculator. To compare a material's density against water or another reference substance, use the specific gravity calculator.