Metal Weight Calculator

Calculating the weight of any metal stock shape follows the same basic relationship: weight equals volume multiplied by density.

Weight = Volume × Density

Volume, in turn, is the cross-sectional area of the shape multiplied by its length. The cross-sectional area formula changes depending on the shape, which is where each stock type differs:

• Round bar: Area = π/4 × D², where D is the diameter
• Square bar: Area = S², where S is the side length
• Flat plate: Area = W × T, where W is width and T is thickness
• Round tube / pipe: Area = π/4 × (OD² − ID²), where OD is outer diameter and ID = OD − 2 × wall thickness
• Hexagonal bar: Area = (√3/2) × AF², where AF is the across-flats dimension (the distance between two parallel faces)
• Equal angle bar (L-shape): Area = t × (2a − t), where a is the leg length and t is the uniform thickness
• Channel (C-shape): Area = t × (2B + H − 2t), where H is the web height, B is the flange width, and t is the uniform thickness

Once the area is known, multiplying by length gives volume, and multiplying volume by the material's density gives weight. Density is a fixed material property (in kg/m³) that varies by metal — steel and cast iron are denser than aluminium, for instance, so an aluminium bar of identical dimensions to a steel bar weighs roughly a third as much.

This calculator also gives a weight per metre figure, which is the standard way stock metal is often priced and specified in catalogues and mill certificates — useful for quickly estimating the weight of a longer or shorter length of the same cross-section without recalculating from scratch.

1. Using outer diameter for a tube's area without subtracting the bore. A pipe or tube's weight comes from the annular (ring-shaped) cross-section only — using the full outer-diameter circle as if it were solid bar dramatically overstates the weight.

2. Confusing across-flats and across-corners for hex bar. Hex bar size is conventionally specified as the across-flats (AF) dimension — the distance between two parallel faces — not the across-corners (larger) dimension; using the wrong one skews the area calculation.

3. Mixing units between dimensions. All dimensions should be in the same unit (this calculator uses millimetres throughout) before multiplying — a width in mm combined with a thickness in cm without converting gives a result that's off by a factor of 10 or 100.

4. Using a generic steel density for a specific alloy. Different steel grades and other alloys have slightly different densities — for precise weight-based costing or freight calculations, confirm the exact grade's density from the mill certificate rather than a rounded reference figure.

5. Forgetting that weight scales with the square of a linear dimension for solid shapes. Doubling the diameter of a round bar quadruples its cross-sectional area (and therefore its weight per unit length), not just doubles it — easy to underestimate when comparing two different stock sizes casually.

6. Not accounting for cut allowance or kerf loss when estimating material needed. The calculated weight is for the finished piece's net dimensions; actual material purchased or consumed is typically somewhat more once saw kerf, cutting allowance, and scrap are factored in.