Weight is just volume times density
Work the three dimensions into the same length unit, multiply for the volume, then multiply by the material density. For carbon steel that density is 7850 kg/m³ (aluminum 2700, so an aluminum plate weighs about a third of the steel one). Keep everything in metres and the answer lands in kilograms.
The one mistake worth avoiding: mixing units
Thickness is almost always quoted in millimetres while length and width are in metres. Feed 10 (mm) straight into the metre formula and you overstate the weight a thousandfold. Convert thickness first.
Carbon-steel plate weight by thickness (per m²)
| Thickness | kg per m² | lb per ft² |
|---|---|---|
| 1 mm | 7.85 | 1.61 |
| 3 mm | 23.6 | 4.83 |
| 5 mm | 39.3 | 8.04 |
| 10 mm | 78.5 | 16.1 |
| 16 mm | 125.6 | 25.7 |
| 20 mm | 157.0 | 32.2 |
| 25 mm | 196.3 | 40.2 |
Per-m² weight depends only on thickness and density — length and width cancel. Multiply by the plate area for the total. Rule of thumb: mm × 7.85 = kg/m².
Same plate, different metals
A 2 m × 1 m × 10 mm plate weighs very differently depending on the metal — density is the whole story.
Aluminum is about 34% the weight of the same steel plate; copper is around 14% heavier than steel.
Common questions
How do I calculate the weight of a steel plate?
Multiply length by width by thickness to get the volume, then multiply by the density. In metric, keep all three dimensions in metres and use 7850 kg per cubic metre for carbon steel. A 2 m x 1 m x 10 mm plate is 2 x 1 x 0.01 x 7850 = 157 kg.
What is the weight of a 1 mm steel sheet per square metre?
About 7.85 kg per square metre. The handy rule for carbon steel is thickness in millimetres times 7.85 equals kilograms per square metre, so 10 mm is roughly 78.5 kg/m2.
Why does my plate weigh more than the calculation?
Usually the real thickness runs over the nominal size within mill tolerance, or a coating like zinc or paint adds mass. Verified densities also vary by grade. Weigh a sample and back-calculate density if it matters.
