A steel weight calculator estimates the theoretical mass of steel bars, plates, tubes and similar sections from their dimensions, length, quantity and material density.
Use the shape selector above for rebar or round bar, square bar, flat bar or plate, round tube and rectangular tube. If you already know a manufacturer's published unit mass for a beam, channel, angle or other steel section, choose Custom Unit Weight.
How to Use the Steel Weight Calculator
- Select the steel shape that matches the item you need to calculate.
- Choose a material density or enter a custom density.
- Enter the dimensions required for the selected shape.
- Enter the length of each piece and the total quantity.
- Optionally enter a steel rate per kg, lb, tonne or US ton.
- Press Calculate Steel Weight to see unit weight, total weight and the calculation steps.
For standard structural sections such as beams, channels and angles, published kg/m or lb/ft values are usually more practical than manually recreating every flange and web dimension. Use the Custom Unit Weight mode for those sections.
Steel Weight Formula
The general theoretical mass formula is:
Weight = Volume × Material Density
First calculate the cross-sectional area of the selected shape. Multiplying cross-sectional area by length gives volume. Multiplying volume by density gives theoretical mass.
For carbon or mild steel, a density near 7,850 kg/m³ is commonly used for theoretical estimates. Stainless grades and other metals can use different densities, which is why this calculator keeps the density visible and editable.
Rebar and Round Bar Weight Formula
For a solid round bar:
Cross-sectional Area = π × Diameter² ÷ 4
Weight = Area × Length × Density
With diameter measured in millimeters, length measured in meters and steel density near 7,850 kg/m³, the common shortcut is:
Weight per meter ≈ D² × 0.006165 kg/m
or approximately
D² ÷ 162.
Standard Rebar Weight per Meter
The following values are theoretical approximations for common metric round reinforcement sizes using standard steel density.
| Bar Diameter | Approx. kg/m | Approx. kg for 12 m |
|---|---|---|
| 6 mm | 0.222 kg/m | 2.66 kg |
| 8 mm | 0.395 kg/m | 4.74 kg |
| 10 mm | 0.617 kg/m | 7.40 kg |
| 12 mm | 0.888 kg/m | 10.66 kg |
| 16 mm | 1.578 kg/m | 18.94 kg |
| 20 mm | 2.466 kg/m | 29.59 kg |
| 25 mm | 3.853 kg/m | 46.24 kg |
| 32 mm | 6.313 kg/m | 75.76 kg |
| 40 mm | 9.864 kg/m | 118.37 kg |
Published manufacturer or standard bar tables should be used where procurement specifications provide nominal unit weights.
Steel Weight Formulas by Shape
| Shape | Cross-Section Formula | Main Inputs |
|---|---|---|
| Round Bar / Rebar | πD² ÷ 4 | Diameter |
| Square Bar | Side² | Side width |
| Plate / Flat Bar | Width × Thickness | Width, thickness |
| Round Tube | π(OD² − ID²) ÷ 4 | Outer diameter, wall thickness |
| Rectangular Tube | WH − (W − 2t)(H − 2t) | Width, height, wall thickness |
| Published Section | Unit Mass × Length | kg/m or lb/ft |
Steel Weight Calculation Examples
Example 1: 12 mm Rebar
For a 12 mm round steel bar:
Unit weight ≈ 12² × 0.006165 = approximately 0.888 kg/m.
For one 12-meter bar:
0.888 × 12 = approximately 10.66 kg.
Ten bars weigh approximately 106.6 kg.
Example 2: Mild-Steel Plate
Suppose a plate is 1,000 mm long × 500 mm wide × 10 mm thick.
Convert to meters: 1.0 × 0.5 × 0.01 m.
Volume = 0.005 m³.
At 7,850 kg/m³: 0.005 × 7,850 = approximately 39.25 kg.
Example 3: Published Structural Section
If a steel section table lists a beam at 18.8 kg/m, and each piece is 6 m long:
18.8 × 6 = 112.8 kg per piece.
Four pieces would have a theoretical total of 451.2 kg. Use Custom Unit Weight mode for this type of calculation.
Theoretical vs Actual Steel Weight
Calculator results are theoretical because they use entered dimensions and a selected density. Actual manufactured steel can differ because of dimensional tolerances, material chemistry, surface scale, coatings and fabrication details.
This difference is especially important when calculating standardized structural sections or commercial rebar. If the manufacturer provides an official unit mass or actual fabricated weight, use that value for procurement, lifting and transport decisions.
Common Steel Weight Calculation Mistakes
Using Nominal Pipe Size as Actual Diameter
Pipe names and nominal sizes do not necessarily equal the physical outer diameter or wall thickness required for a geometric weight calculation. Use actual dimensions from the product specification.
Mixing Millimeters and Meters
Cross-section dimensions are often entered in millimeters while piece length is measured in meters. They must be converted consistently before volume is calculated. This calculator performs those conversions internally.
Using Solid-Bar Formula for Hollow Tube
Tube weight must exclude the empty interior. The calculator subtracts the inner cross-sectional area from the outer area before calculating weight.
Assuming Every Steel Grade Has Exactly the Same Density
Many carbon-steel calculations use about 7,850 kg/m³, but stainless steels and other materials may use different theoretical densities. Choose the closest material or enter a custom density.
Ignoring Published Section Unit Weight
For I-beams, channels, angles and other standard sections, manufacturer or standard tables often publish kg/m or lb/ft. Using that published unit weight is generally simpler and more appropriate than recreating complex geometry manually.
How to Verify Your Steel Weight Estimate
- Confirm that the selected shape matches the real steel product.
- Check every dimension and measurement unit.
- Confirm the piece length and quantity.
- Use the correct material density.
- For rebar, compare kg/m with the supplier or standard bar table.
- For structural sections, compare against the published section mass.
- For lifting or transport, use verified actual weight when required.
How we calculate: Utilixea calculates cross-sectional area from the selected geometry, converts the dimensions to meters, multiplies area by length to obtain volume, and then multiplies volume by the selected material density. Custom Unit Weight mode uses the entered kg/m or lb/ft directly.
Planning other construction materials? Try the Concrete Volume Calculator, Cement Calculator, or browse all Material Estimation Calculators.
Frequently Asked Questions
The general formula is volume × material density. First calculate the cross-sectional area of the steel shape, multiply that area by length, then multiply the resulting volume by density.
D²/162 is a common shortcut for estimating the theoretical weight of round steel reinforcement in kilograms per meter when diameter D is measured in millimeters.
A 12 mm round steel bar has a theoretical unit weight of approximately 0.888 kg per meter when calculated using a steel density near 7,850 kg/m³.
The theoretical unit weight of a 16 mm round steel bar is approximately 1.58 kg per meter.
Multiply plate width × thickness to obtain cross-sectional area, multiply by plate length to obtain volume, then multiply by the selected steel density.
For a round tube, subtract the inner-circle area from the outer-circle area, then multiply the remaining steel area by length and material density. Use actual outer diameter and wall thickness rather than nominal pipe size.
Theoretical calculations use entered dimensions and nominal material density. Actual products can differ because of manufacturing tolerances, material composition, scale, coatings and fabrication details.
A theoretical result is useful for preliminary estimating, but critical lifting and transport decisions should use verified manufacturer, fabricator or measured weights whenever required by the project.
Calculation methodology: Utilixea · Last updated: July 24, 2026
