Square Bar Weight per Meter: Chart (6–50 mm), Formula and Examples
Picture this. Your drawing says "20 mm square bar, 6 m long." The supplier quotes you per kilogram. The transporter wants a total weight. And nobody has told you what the bar actually weighs.
Good news: you are one multiplication away from the answer.
Short answer: for mild steel, square bar weight (kg per meter) = side in mm × side in mm × 7.85 ÷ 1000. A 20 mm square bar works out to 3.14 kg per meter, so a 6 m length weighs about 18.84 kg.
Key Takeaways
- Mild steel square bar: kg/m = side² × 0.00785 (the side is in millimeters).
- Quick shortcut: side² ÷ 127.4 gives almost the same number.
- The formula uses a steel density of 7,850 kg/m³. For other metals, swap in their density.
- Square bar is about 27% heavier than a round bar whose diameter equals the square's side.
- These are theoretical weights. Real bars vary slightly, so use your supplier's figures for anything critical.
The Square Bar Weight Formula
A square bar is just a long, square-shaped block. Its weight is volume times density, and the volume is the cross-section area times the length.
Metric formula (mild steel):
Weight per meter (kg/m) = Side (mm) × Side (mm) × 7.85 ÷ 1000
Where does 7.85 come from? Mild steel has a density of about 7,850 kg/m³ (7.85 g/cm³). The Engineering ToolBox density table lists steel at 7,850 kg/m³.
General formula for any metal:
Weight per meter (kg/m) = Side (mm) × Side (mm) × Density (kg/m³) ÷ 1,000,000
Imperial version (steel):
Weight per foot (lb/ft) ≈ Side (in) × Side (in) × 3.4
Total weight of a piece:
Total weight = Weight per meter × Length in meters
Worked Example 1: 20 mm square bar
- 20 × 20 = 400
- 400 × 7.85 ÷ 1000 = 3.14 kg per meter
- For a 6 m length: 3.14 × 6 = 18.84 kg
That is why the "20mm square bar weight" is such a handy number to remember. It happens to come out as 3.14.
Worked Example 2: 25 pieces of 12 mm bar, 3 m each
- 12 × 12 = 144
- 144 × 7.85 ÷ 1000 = 1.1304 kg per meter
- One piece: 1.1304 × 3 = 3.3912 kg
- 25 pieces: 3.3912 × 25 = 84.78 kg
Worked Example 3: How many meters in one tonne of 16 mm bar?
- 16 × 16 = 256
- 256 × 7.85 ÷ 1000 = 2.0096 kg per meter
- 1,000 kg ÷ 2.0096 = about 498 meters
Square Bar Weight Chart (Mild Steel, 6 mm to 50 mm)
Every value below uses the formula above with 7,850 kg/m³. Weights are theoretical and rounded.
| Side (mm) | Weight (kg per meter) | Weight of a 6 m length (kg) |
|---|---|---|
| 6 | 0.283 | 1.70 |
| 8 | 0.502 | 3.01 |
| 10 | 0.785 | 4.71 |
| 12 | 1.130 | 6.78 |
| 14 | 1.539 | 9.23 |
| 16 | 2.010 | 12.06 |
| 18 | 2.543 | 15.26 |
| 20 | 3.140 | 18.84 |
| 22 | 3.799 | 22.80 |
| 25 | 4.906 | 29.44 |
| 28 | 6.154 | 36.93 |
| 30 | 7.065 | 42.39 |
| 32 | 8.038 | 48.23 |
| 36 | 10.174 | 61.04 |
| 40 | 12.560 | 75.36 |
| 45 | 15.896 | 95.38 |
| 50 | 19.625 | 117.75 |
A handy pattern: double the side and the weight goes up four times. A 40 mm bar weighs four times as much as a 20 mm bar (12.56 vs 3.14 kg/m), because area depends on the side squared.
Need to convert? 1 kg/m is about 0.672 lb/ft. So the 20 mm bar at 3.14 kg/m is roughly 2.11 lb/ft.
Square Bar Weight for Stainless Steel, Aluminium, Brass and Copper
The formula stays the same. Only the density changes. Here is how the other common metals compare, using a 20 mm square bar as the example.
| Metal | Typical density (kg/m³) | Multiplier vs mild steel | 20 mm bar (kg/m) |
|---|---|---|---|
| Mild steel | 7,850 | 1.00 | 3.14 |
| Stainless steel (304 / 316 range) | 7,900–8,000 | 1.01–1.02 | 3.16–3.20 |
| Aluminium | about 2,700 | 0.34 | 1.08 |
| Brass | 8,400–8,730 | 1.07–1.11 | 3.36–3.49 |
| Copper | about 8,940 | 1.14 | 3.58 |
Density changes a little between alloys and grades, so treat these as typical values and check the data sheet for your exact material.
Square Bar vs Round Bar: Which Is Heavier?
If both bars have the same measurement (a 20 mm square side and a 20 mm round diameter), the square bar is heavier. A square with side a has an area of a². A circle with diameter a has an area of π/4 × a², which is about 0.785 × a².
Divide one by the other and you get roughly 1.27. So the square bar is about 27% heavier.
Working with other shapes too? Our guide on how to calculate steel weight covers plate, flat bar, round bar and pipe.
Common Mistakes (and How to Avoid Them)
- Using the round bar formula. Square bars use side × side, not diameter. Mixing them up gives you the wrong answer by about 27%.
- Mixing units. The metric formula needs the side in millimeters and gives kg per meter. If you measure in centimeters or inches, convert first.
- Using steel density for every metal. Aluminium is far lighter than steel, and brass and copper are heavier. Use the right density.
- Treating the result as exact. Real bars have manufacturing tolerances, and many have slightly rounded corners. Actual weight can differ a little from the theoretical figure.
- Measuring the wrong thing. For a square bar, use the length of one side, not the diagonal.
Quick Checklist
- Measure the side of the bar in millimeters.
- Square it (side × side).
- Multiply by 7.85 and divide by 1000 for mild steel, or use the density for your metal.
- Multiply by the length in meters.
- Add a sensible allowance if the weight matters for cost, handling or transport.
Frequently Asked Questions
How do you calculate the weight of a square bar?
Multiply the side by itself (in mm), multiply by 7.85, divide by 1000, and you get kilograms per meter for mild steel. Multiply by the length in meters for the total weight.
What is the weight of a 20 mm square bar per meter?
What is the weight of a 20 mm square bar per meter?
How much does a 12 mm square bar weigh?
A 12 mm mild steel square bar weighs about 1.13 kg per meter.
Is a square bar heavier than a round bar?
Yes, when the side of the square equals the diameter of the round. The square bar is roughly 27% heavier because it has more cross-section area.
How do I calculate stainless steel square bar weight?
Use the same formula with a stainless steel density, typically somewhere between 7,900 and 8,000 kg/m³. In practice, the result is only about 1 to 2% higher than mild steel.
Why is the weight I measured different from the calculated weight?
The formula gives a theoretical weight. Tolerances, rounded corners, density differences between grades and even weighing errors can all make real bars a bit heavier or lighter.
Final Thoughts
Once you remember one line, side × side × 7.85 ÷ 1000, you can work out the weight of any mild steel square bar in your head. Whether it is a single 20 mm bar or a full order, the maths is the same.
And if you would rather not do it by hand every time, the free Square Bar Weight Calculator on BytePriva can do it in a few seconds.
Disclaimer
This guide is for general information and educational purposes only. All weights are theoretical, calculated with typical material densities and rounded for readability. Real products vary in size tolerance, corner radius, alloy and density, so actual weights can differ. For purchasing, structural design, lifting, load limits, shipping or any safety-critical decision, always rely on your supplier's specification or mill certificate and, where needed, a qualified engineer. The external link is provided for reference only; we do not control its content. Nothing in this article is professional, engineering, legal or purchasing advice.