What Is the Rectangular Plate Weight Calculator?
This calculator estimates the weight of a flat rectangular plate or sheet of any material from three dimensions — length, width, and thickness — and the material's density. It is widely used in metal fabrication, engineering, shipping cost estimation, and DIY projects to predict how heavy a finished piece of steel, aluminum, copper, brass, or any other solid material will be before you cut it.
How to Use It
Enter the plate's length, width, and thickness in millimetres, then enter the material density in grams per cubic centimetre (g/cm³). Common densities are pre-listed: steel ≈ 7.85, aluminum ≈ 2.70, copper ≈ 8.96, and brass ≈ 8.50. The calculator returns the weight in kilograms, grams, and pounds, plus the plate's volume in cubic centimetres.
The Formula Explained
The weight of a solid object equals its volume times its density: $$\text{Weight} = l \times w \times t \times \text{density}$$. Because dimensions are entered in millimetres and density is in g/cm³, each length is divided by 10 to convert millimetres to centimetres. The product of the three converted dimensions gives volume in cm³, which multiplied by density (g/cm³) gives weight in grams. Dividing by 1,000 converts grams to kilograms.
$$\text{Weight (kg)} = \frac{\dfrac{\text{Length (mm)}}{10} \times \dfrac{\text{Width (mm)}}{10} \times \dfrac{\text{Thickness (mm)}}{10} \times \text{Density (g/cm}^3\text{)}}{1000}$$
Worked Example
A steel plate measuring 1000 mm × 500 mm × 10 mm with a density of 7.85 g/cm³: convert to cm → \(100 \times 50 \times 1 = 5{,}000 \text{ cm}^3\). Weight $$= 5{,}000 \times 7.85 = 39{,}250 \text{ g} = 39.25 \text{ kg} \approx 86.5 \text{ lb}$$
FAQ
Which density should I use? Use the published density of your specific alloy or material. Mild steel is about 7.85 g/cm³, while stainless varies between 7.7 and 8.0.
Can I use it for non-metals? Yes — any solid material works as long as you supply the correct density (e.g. acrylic ≈ 1.18, glass ≈ 2.5).
Does it account for holes or chamfers? No. It assumes a perfectly solid rectangular block, so cutouts will slightly reduce actual weight.
