Round Bar Weight Formula & Calculator

Round bar weight comes from the circular area A = πd²/4 times length and material density. The same formula works for steel, aluminum, stainless, brass, bronze and plastics once the density changes.

Round bar formula

For a solid round bar, cross-section area is A = π · d² / 4. Weight is: W = ρ · (πd²/4) · L With d and L in millimetres and density in g/cm³, weight (kg) = ρ · π · d² · L / 4,000,000.

Weight per metre is even simpler: kg/m = ρ · π · d² / 4000. For steel at 7.85 g/cm³, that becomes kg/m = 0.006165 · d² with d in mm.

Worked example

A 25 mm steel round bar weighs 0.006165 × 25² = 3.85 kg/m. A 2 m piece weighs 3.85 × 2 = 7.70 kg. If the same bar were 6061 aluminum, the density ratio is 2.70 / 7.85, so the weight would be about 2.65 kg.

Diameter matters more than length

Round bar weight scales with the square of diameter. Doubling the diameter from 25 mm to 50 mm makes the bar four times heavier per metre, not twice as heavy. Length scales linearly, so a 6 m stock bar is exactly six times the 1 m weight before tolerances.

Solid bar versus tube

Round tube and pipe subtract the bore area from the outside circle, so they can be much lighter than solid round bar at the same outside diameter. For tube or nominal pipe, use the pipe weight formula or open the calculator with the round tube shape selected.

Related material tools

Metal weight calculator for bar, tube, plate, angle and material changes.
Material density chart for steel, aluminum, stainless, brass, bronze, titanium and plastics.
Steel pipe schedule chart for nominal pipe sizes, wall thickness and IDs.
Steel weight formula for a focused formula and worked example.
Aluminum weight formula for a focused formula and worked example.
Stainless steel weight formula for a focused formula and worked example.
Plate weight formula for a focused formula and worked example.
Pipe weight formula for a focused formula and worked example.
Square tube weight formula for a focused formula and worked example.
Rectangular tube weight formula for a focused formula and worked example.

Last reviewed: June 1, 2026.