What formula is used to calculate iron hexagon bar weight?

The formula is: Weight = (√3/2) × AF² × Length × Density. AF (across-flats) and length are converted to meters. The cross-section area of a regular hexagon expressed in terms of across-flats distance is (√3/2) × AF². Multiplying by length gives volume (m³), and multiplying by material density (kg/m³) gives weight in kilograms.

What is the across-flats (AF) dimension?

The across-flats (AF) dimension, also called "width across flats" or "wrench size", is the distance between two parallel flat sides of a hexagonal bar. It is the standard measurement used for hex bolts, nuts, and hex stock. It differs from the across-corners dimension, which equals AF × (2/√3) ≈ AF × 1.155.

What density is used for mild steel?

Mild steel (low-carbon steel) has a standard density of 7850 kg/m³, which is the most commonly used value in engineering calculations. Stainless steel grades 304 and 316 are slightly denser at 7900 and 8000 kg/m³ respectively. Cast iron is around 7200 kg/m³.

Does this calculator support metric and imperial units?

Yes. The across-flats dimension can be entered in mm, cm, or inches. Bar length can be entered in meters, mm, feet, or inches. All values are converted to meters internally before the calculation.

How does hexagon bar weight compare to round bar of the same nominal size?

A hexagon bar is heavier than a round bar of the same nominal (AF) diameter. The hexagon cross-section area is (√3/2) × AF² ≈ 0.866 × AF², whereas the round bar area is (π/4) × D² ≈ 0.785 × D². So a hex bar weighs about 10% more than a round bar of the same nominal size.

Can I calculate the total weight for multiple bars?

Yes. Enter the number of bars in the Quantity field and the calculator will show both the per-bar weight and the total weight for the entire batch.

Iron Hexagon Bar Weight Calculator

Name: Iron Hexagon Bar Weight Calculator
Availability: InStock
Author: Nham Vu

Enter the across-flats size, bar length, and material grade to instantly calculate iron or steel hexagon bar weight in kg and lbs.

Bar Dimensions

Across-Flats (AF)

Distance between two parallel flat sides (wrench size).

Bar Length

Material Grade

Quantity (bars)

Formula Reference

W = (√3/2) × AF² × L × ρ

Where AF = across-flats (m), L = bar length (m), ρ = material density (kg/m³), W = weight (kg). Cross-section area = (√3/2) × AF² ≈ 0.866 × AF².

Enter dimensions on the left and click Calculate.

Iron and Steel Densities

Material	Grade / Use	kg/m³	lb/in³
Mild Steel	Low-Carbon / Structural	7850	0.2836
Carbon Steel	Medium / High Carbon	7860	0.2839
SS 304	Stainless Steel 304	7900	0.2854
SS 316	Stainless Steel 316	8000	0.2890
Alloy Steel	Chromoly / Engineering	7750	0.2800
Tool Steel	H13, D2, M2	8000	0.2890
Gray Cast Iron	General Casting	7200	0.2601
Ductile Iron	Nodular / SG Iron	7700	0.2782
Wrought Iron	Decorative / Traditional	7750	0.2800

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Summary

Enter the across-flats size, bar length, and material grade to instantly calculate iron or steel hexagon bar weight in kg and lbs.

How it works

Enter the across-flats (AF) dimension of the hexagon bar in millimeters, inches, or centimeters.
Enter the bar length in meters, millimeters, feet, or inches.
Select the material grade from the dropdown (mild steel, stainless, cast iron, etc.).
Optionally enter a quantity for multiple bars.
The calculator applies W = (√3/2) × AF² × L × ρ and shows weight in kg and lbs.
Click Copy to save the result to your clipboard.

Use cases

Estimating steel hexagon bar weight for machining, CNC turning, and lathe work.
Calculating freight and shipping weight for hex bar stock orders.
Preparing bill of materials (BOM) for bolt, nut, and fastener manufacturing.
Verifying load limits on lifting and material handling equipment.
Cost estimation for iron and steel hex bar purchases priced by weight.
Material planning for valve bodies, fittings, and hydraulic components.
Structural calculations for iron hex bar used in construction and fabrication.
Comparing hex bar vs. round bar weight for the same nominal size.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu