Round Bar & Shaft Weight Calculator

Round Bar Weight per Meter Chart (Mild Steel)

The D²/162 formula is a quick shortcut for Mild Steel round bars. Simply square the diameter in mm and divide by 162 to get the weight per meter in kg. For example, a 25mm bar: 25² / 162 = 3.858 kg/m (the exact constant 162.2 gives 3.853 kg/m). This shortcut is derived from the full formula π/4 × D² × ρ, where ρ for MS is 7850 kg/m³.

For other materials, the divisor changes based on density: roughly D²/160.5 for SS 304, D²/472 for Aluminium (2700 kg/m³), D²/142 for Copper (8940 kg/m³) and D²/150 for Brass (8500 kg/m³). However, the calculator above handles all materials automatically — just select from the dropdown.

Understanding the D²/162 Formula — Where Does 162 Come From?

The D²/162 formula is the most widely used shortcut in the Indian steel industry for quickly estimating the weight of mild steel round bars. But where does the magic number 162 come from?

The full formula for weight per meter of a solid round bar is: W = π/4 × D² × 1m × ρ. Substituting ρ = 7850 kg/m³ and converting D from mm to meters (dividing by 1000):

W = π/4 × (D/1000)² × 1 × 7850 = D² × (π × 7850) / (4 × 1000000) = D² / 162.19

Rounded to 162, this gives you the weight per meter in kg when D is in mm. Rounding 162.19 to 162 changes the result by only about 0.1%, which is far smaller than the rolling tolerance of real bars.

Quick mental math trick: For common sizes, memorize that a 10mm bar weighs about 0.617 kg/m. Since weight scales with the square of diameter, a 20mm bar (2× diameter) weighs 4× more = 2.466 kg/m, and a 40mm bar (4× diameter) weighs 16× more = 9.865 kg/m.

Round Bar vs TMT Bar — Weight and Application Differences

Plain round bars (also called bright bars or MS rods) have a smooth surface and are used in machining, fabrication, shafts, pins, bolts, and general engineering. They are available in hot-rolled and cold-drawn finishes. Cold-drawn bars have tighter dimensional tolerances and a smoother surface.

TMT bars (Thermo-Mechanically Treated bars) have a ribbed surface pattern that provides better bonding with concrete. They are exclusively used as reinforcement in RCC (Reinforced Cement Concrete) construction — foundations, columns, beams, slabs, and retaining walls.

Both have the same theoretical weight per meter for the same diameter, since the density of steel is the same (7850 kg/m³). For TMT (ribbed) bars, IS 1786 defines the nominal mass per metre from the nominal diameter using this same relation, so the D²/162 formula gives the standard nominal weight for both types. Actual TMT bars are accepted within the IS 1786 mass tolerance.

TMT bars in India are graded by yield strength: Fe 415, Fe 500, Fe 500D (most common for residential), and Fe 550D (for high-rise and infrastructure). The grade affects strength, not weight — a 12mm Fe 500D bar weighs the same as a 12mm Fe 415 bar.

Common Round Bar Sizes and Their Applications in India

Standard supply length for round bars in India is 6 meters for sizes up to 25mm and 6 or 12 meters for larger sizes. TMT bars are typically supplied in 12-meter lengths and can be cut to size on request. Bright (cold-drawn) bars are available in 3-meter and 6-meter lengths.

Round Bar Weight in Different Materials — SS, Aluminium, Copper

The same π/4 × D² × L × ρ formula applies to all materials. The only variable that changes is the density (ρ). Here is how a 25mm × 1-meter round bar compares across common engineering materials:

Aluminium is about one-third the weight of steel, making it ideal for aerospace and lightweight applications. Copper and brass are heavier than steel and are used for electrical conductors, plumbing fittings, and decorative work. Select any material in the calculator above to get instant results.