Weight of round bars (rebar), square bars and flat bars / plates.
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Steel Weight Calculator: Free Online Tool
The Steel Weight Calculator finds the weight of round bars (rebar), square bars and flat bars or plates. You select the section, enter the diameter or the side, or the width and thickness for a flat bar, then give the length of one piece and the number of pieces. It returns the weight per metre, the weight per foot, the total length and the total weight in kilograms, tonnes and pounds.
Site engineers, store keepers, steel fabricators and students use it to check reinforcement delivery, prepare bar bending schedules and compare supplier bills. Steel is sold by weight, so a small error in the weight per metre can change the cost of a large order considerably. A quick calculation helps you verify that the quantity received matches the quantity billed.
When to use this calculator
Use this calculator when steel arrives on site and you want to check the delivered weight against the challan. It is useful for converting a bar bending schedule from length to weight, for estimating the cost of reinforcement, and for planning transport. Fabricators can find the weight of flat bars, plates and square sections for gates, grills and frames. Students can use it to verify examples. You can also use it to see how much heavier a larger diameter bar is compared with a smaller one.
How to use the Steel Weight Calculator
- Open the calculator above on your phone, tablet or computer. Nothing needs to be installed and no sign-up is required.
- Choose the unit system first (feet / inches or metres / mm). The input labels change to match your choice.
- Pick the option you need from the drop-down list (Round bar (rebar); Square bar; Flat bar / plate).
- Enter your values in the input boxes: Section, Bar diameter (mm), Width (mm), Thickness (mm), Length of one piece (ft), Number of pieces. The boxes already hold sample values, so overwrite them with your own.
- Press Calculate. The result appears straight away under the button.
- Change any value and press Calculate again to compare options. Press Reset to go back to the sample values.
- Check the result against your drawings, project specification and local code before you order material or approve work.
How the calculation works
The calculator uses a steel density of 7850 kg/m³. The cross-sectional area is calculated first: (pi/4) x d² for a round bar, side x side for a square bar, and width x thickness for a flat bar, all in mm². Weight per metre is the area in m² multiplied by 7850. For a round bar this is about d²/162 kg per metre, with d in mm. Total length is the length of one piece multiplied by the number of pieces, and the total weight is the weight per metre multiplied by the total length. The default is a 12 mm bar, 40 ft long, 10 pieces.
Worked example
When you open the page the calculator is filled with sample values. Pressing Calculate with those values gives the result below, which you can use to check that you are reading the output correctly.
| Steel weight (density 7850 kg/m³) | |
|---|---|
| Weight per metre | 0.888 kg/m |
| Weight per foot | 0.271 kg/ft |
| Total length | 121.92 m (400.0 ft) |
| Total weight | 108.24 kg |
| Total weight (tonnes) | 0.1082 t |
| Total weight (lb) | 238.6 lb |
Tips and common mistakes
- Enter the nominal bar diameter in millimetres. Delivered bars may be slightly over or under size, so a small difference from the challan is normal.
- Use the correct section. A square bar with a side equal to a round bar's diameter weighs more, because its cross-sectional area is larger.
- For flat bars, enter width and thickness in millimetres, not inches. Check the unit before calculating, since a thickness error greatly changes the weight.
- Remember that length of one piece is in feet or metres according to the unit system selected, while the section size is always in millimetres.
- Add laps, hooks and bends to the bar length from the bar bending schedule, because the calculator only weighs the length you enter.
Frequently asked questions
What formula gives the weight of a round bar?
Weight per metre is (pi/4) x d² x 7850 kg/m³, with d converted from mm to m. In simple form this is about d²/162 kg per metre, where d is the diameter in mm. Both values are shown in the result.
What density is used for steel?
The calculator uses 7850 kg/m³ for all sections. This is a standard value for steel, and it is stated in the result heading so that you can verify the calculation by hand. You can repeat the calculation by hand.
What is the weight of a 12 mm bar per metre?
Using d²/162 with 12 mm, the weight is about 0.888 kg per metre. The calculator shows this value, and the weight per foot, which is about 0.271 kg. Square the diameter and divide by 162 to check it quickly.
Can I calculate plates and flat bars?
Yes. Choose flat bar or plate, then enter its width and thickness in millimetres. The calculator multiplies the area by the density, and then by the length and number of pieces you enter. The same density of 7850 kg/m³ is used for all sections.
Does it give weight in pounds and tonnes?
Yes. The result shows total weight in kilograms, tonnes and pounds, so you can compare it with supplier documents that use different units.
Important note
This tool gives estimates for planning, study and quick checks. It does not replace design by a qualified engineer, site-specific testing, or the requirements of your project specification and local building code. Always confirm final quantities, test results and acceptance limits with the responsible engineer before using them for construction or payment.
