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Calculate the weight of any steel shape using the steel weight formula W = V × D. Supports round bars, plates, tubes, angles, I-beams, and the rebar formula D²/162. Choose from carbon steel, stainless steel, alloy steel, and tool steel types.
Carbon Steel Density
7,850 kg/m³ (0.284 lb/in³)
Rebar Formula
W(kg/m) = D² / 162
Unit Weight of Steel
78.5 kN/m³ (490 lb/ft³)
The fundamental steel weight formula used in engineering and construction is Weight = Volume × Density. This simple equation applies to every steel shape, from thin sheet metal to massive structural I-beams. The volume depends on the cross-sectional geometry of the steel piece, and the density of steel depends on its composition and alloying elements.
For carbon steel with a density of 7,850 kg/m³, a piece with a volume of 0.001 m³ weighs exactly 7.85 kg. The challenge lies in calculating the volume correctly for different shapes. A round bar uses the formula V = π × (D/2)² × L, while a flat plate uses V = W × H × L. Hollow sections like tubes require subtracting the inner void from the outer volume.
The formula W(kg/m) = D² / 162 is the most widely used shortcut for calculating the weight of round steel bars and rebar on construction sites. This formula gives the weight per meter of a round carbon steel bar, where D is the nominal diameter in millimeters. It is derived from the full formula by substituting the standard density of steel (7,850 kg/m³) and simplifying.
This formula works for all round steel bars, not just rebar. It is accurate for carbon steel and provides a quick estimate for other steel types. Engineers on job sites use it to rapidly calculate material weights for ordering, crane load planning, and structural analysis without needing a calculator for the full formula. For total weight, simply multiply the per-meter result by the total length of the bar in meters.
To quickly estimate rebar weight: a 10 mm bar weighs about 0.6 kg/m, a 12 mm bar about 0.9 kg/m, a 16 mm bar about 1.6 kg/m, a 20 mm bar about 2.5 kg/m, and a 25 mm bar about 3.9 kg/m. These values scale with the square of the diameter, so doubling the diameter quadruples the weight per meter.
Different steel types have different densities due to their chemical composition. Choosing the correct density is critical for accurate weight calculations. Carbon steel is the most common type used in general construction, while stainless steel grades offer superior corrosion resistance for marine, chemical, and food processing environments. Alloy steel and tool steel serve specialized mechanical and industrial applications.
| Steel Type | Density (kg/m³) | Density (lb/in³) | Key Properties | Common Uses |
|---|---|---|---|---|
| Carbon Steel (Mild) | 7,850 | 0.284 | Weldable, ductile, affordable | Rebar, beams, plates, pipes |
| Stainless Steel 304 | 8,000 | 0.289 | Corrosion resistant, 18% Cr / 8% Ni | Kitchen, food processing, architecture |
| Stainless Steel 316 | 8,027 | 0.290 | Superior corrosion resistance, Mo added | Marine, chemical plants, medical devices |
| Alloy Steel | 7,750 | 0.280 | High strength, heat treatable | Gears, shafts, heavy machinery |
| Tool Steel | 7,830 | 0.283 | Extreme hardness, wear resistance | Cutting tools, dies, molds |
Stainless steel grades 304 and 316 provide excellent corrosion resistance thanks to their chromium content, which forms a passive oxide layer on the surface. This makes them ideal for environments exposed to moisture, salt, and chemicals. Carbon steel, while less expensive, requires protective coatings such as paint, galvanizing, or epoxy to prevent rust in exposed applications.
The unit weight of steel is the weight per unit volume, commonly expressed in different unit systems depending on the region and application. Engineers use these standardized values for structural analysis, load calculations, and material estimation. The table below shows the unit weight of carbon steel (density 7,850 kg/m³) in all commonly used unit systems.
| Unit System | Unit Weight Value | Unit | Common Use |
|---|---|---|---|
| SI (Metric) | 7,850 | kg/m³ | International engineering |
| SI (kN) | 78.5 | kN/m³ | Structural analysis |
| Imperial | 490 | lb/ft³ | US construction |
| Imperial | 0.284 | lb/in³ | Machine design |
| Metric (g/cm³) | 7.85 | g/cm³ | Lab / material science |
| Metric (kg/dm³) | 7.85 | kg/dm³ | European standards |
This comprehensive rebar weight chart covers all standard bar sizes from #3 through #18 per ASTM A615. Weights are calculated using the D²/162 steel weight formula for carbon steel bars. These values are essential for estimating material quantities, calculating dead loads, and planning reinforcement schedules on construction projects.
| Bar Size | Diameter (mm) | Diameter (in) | kg/m | lb/ft | Weight per 20 ft (lbs) |
|---|---|---|---|---|---|
| #3 | 9.525 | 0.375 | 0.560 | 0.376 | 7.52 |
| #4 | 12.700 | 0.500 | 0.994 | 0.668 | 13.36 |
| #5 | 15.875 | 0.625 | 1.556 | 1.043 | 20.86 |
| #6 | 19.050 | 0.750 | 2.240 | 1.502 | 30.04 |
| #7 | 22.225 | 0.875 | 3.049 | 2.044 | 40.88 |
| #8 | 25.400 | 1.000 | 3.982 | 2.670 | 53.40 |
| #9 | 28.650 | 1.128 | 5.071 | 3.400 | 68.00 |
| #10 | 32.260 | 1.270 | 6.404 | 4.303 | 86.06 |
| #11 | 35.810 | 1.410 | 7.907 | 5.313 | 106.26 |
| #14 | 43.000 | 1.693 | 11.384 | 7.650 | 153.00 |
| #18 | 57.330 | 2.257 | 20.284 | 13.600 | 272.00 |
Structural steel sections come in standardized profiles with published weights per unit length. The table below lists common wide-flange (W-shape) steel beams used in building construction and bridge engineering. These unit weights include the web, flanges, and fillets of the cross-section.
| Section | Depth (mm) | Flange Width (mm) | kg/m | lb/ft |
|---|---|---|---|---|
| W150x13 | 148 | 100 | 13.0 | 8.7 |
| W200x15 | 200 | 100 | 15.0 | 10.1 |
| W200x22 | 206 | 102 | 22.0 | 14.8 |
| W250x25 | 257 | 102 | 25.3 | 17.0 |
| W310x33 | 313 | 102 | 32.7 | 22.0 |
| W310x44 | 310 | 166 | 44.0 | 29.6 |
| W360x51 | 355 | 171 | 51.0 | 34.2 |
| W410x60 | 407 | 178 | 60.0 | 40.3 |
| W460x74 | 457 | 190 | 74.0 | 49.7 |
| W530x92 | 533 | 209 | 92.0 | 61.8 |
| W610x113 | 612 | 228 | 113.0 | 75.9 |
Accurate steel weight calculations are the foundation of structural engineering. Dead load from steel members must be precisely known to design safe foundations, columns, and connections. Underestimating weight can lead to structural failure, while overestimating wastes material and budget.
Steel is priced by weight. Knowing the exact weight of steel bars, plates, and structural sections lets you accurately estimate project costs. A 5% error on a 100-ton steel order means 5 tons of wasted budget or unexpected shortfall on the job site.
Every lift on a construction site requires knowing the weight of steel being moved. Crane capacity charts are based on load weight and radius. Incorrect weight estimates risk crane overload incidents and transportation violations for overweight loads.
When steel arrives at a job site, weighing it against calculated values verifies that the correct grade and dimensions were delivered. A significant weight discrepancy can indicate wrong steel types, incorrect dimensions, or missing pieces from the order.
The most common error in steel weight calculations is mixing units. If your dimensions are in millimeters, convert them to meters before multiplying by density in kg/m³. Divide mm by 1,000 to get meters, or divide mm³ by 1,000,000,000 to get m³.
Do not assume all steel has the same density. Carbon steel (7,850 kg/m³) and stainless steel 316 (8,027 kg/m³) differ by over 2%. On a large order, using the wrong density can result in tons of error in your weight estimate.
The rebar formula D²/162 is specifically calibrated for carbon steel at 7,850 kg/m³. For stainless steel rebar, the result will underestimate weight by about 2%. For non-round shapes like square bars or flat bars, use the general volume formula instead.
Actual steel dimensions may vary from nominal values by up to 5% due to manufacturing tolerances. Hot-rolled sections typically weigh within ±2.5% of calculated values. For critical applications, always add a 3-5% contingency to your weight estimates.
When calculating tube or pipe weight, you must subtract the inner void. A common mistake is calculating a solid section instead of a hollow one. A 50 mm OD tube with 3 mm walls has far less cross-sectional area than a 50 mm solid bar.
US rebar sizes (#3, #4, etc.) are in eighths of an inch, while metric sizes use millimeter diameters. A #4 bar is 12.7 mm (1/2 inch), not 4 mm. Confusing these systems will produce wildly inaccurate weight calculations. Always confirm which sizing standard your project uses.
The basic steel weight formula is Weight = Volume x Density. For any steel shape, calculate the cross-sectional area, multiply by the length to get volume, then multiply by the density of steel (typically 7,850 kg/m3 for carbon steel). For round steel bars specifically, the shortcut formula W(kg/m) = D squared / 162 is widely used, where D is the diameter in millimeters.
The density of steel varies by type. Carbon steel (mild steel) has a density of 7,850 kg/m3. Stainless steel 304 is 8,000 kg/m3. Stainless steel 316 is 8,027 kg/m3. Alloy steel averages 7,750 kg/m3. Tool steel is approximately 7,830 kg/m3. These values are standard references used in engineering calculations worldwide.
To calculate steel plate weight, use the formula: Weight = Length x Width x Thickness x Density. For example, a carbon steel plate measuring 2,000 mm x 1,000 mm x 10 mm weighs: (2.0 x 1.0 x 0.01) x 7,850 = 157 kg. Always convert all dimensions to meters before multiplying by the density in kg/m3.
D squared / 162 is the famous rebar weight formula used on construction sites worldwide. D is the bar diameter in millimeters, and the result is weight in kg per meter. The formula is derived from the full equation: (pi/4) x D squared x density, simplified using steel density of 7,850 kg/m3. For example, a 16 mm bar weighs 16x16/162 = 1.58 kg/m.
For a round steel tube, calculate the volume of the outer cylinder minus the inner cylinder, then multiply by density. The formula is: Weight = pi x ((OD/2) squared - (ID/2) squared) x Length x Density. The inner diameter equals the outer diameter minus twice the wall thickness. For a 50 mm OD tube with 3 mm wall and 6 m length in carbon steel: pi x (625 - 484) x 6000 / 1e9 x 7850 = 19.75 kg.
The unit weight of steel depends on the cross-section. For common rebar sizes: 10 mm bar = 0.617 kg/m (0.414 lb/ft), 12 mm = 0.888 kg/m (0.597 lb/ft), 16 mm = 1.580 kg/m (1.061 lb/ft), 20 mm = 2.469 kg/m (1.658 lb/ft), 25 mm = 3.858 kg/m (2.591 lb/ft). Multiply kg/m by 0.672 to get lb/ft.
Yes, stainless steel is slightly heavier than carbon steel. Carbon steel has a density of 7,850 kg/m3, while stainless steel 304 is 8,000 kg/m3 and stainless steel 316 is 8,027 kg/m3. This means stainless steel is about 2% heavier. The added weight comes from chromium and nickel alloying elements that provide corrosion resistance.
The weight depends on the bar diameter. A standard 20-foot (6.1 m) length weighs: #3 (10 mm) = 3.76 kg (8.3 lbs), #4 (13 mm) = 6.41 kg (14.1 lbs), #5 (16 mm) = 9.63 kg (21.2 lbs), #6 (19 mm) = 13.6 kg (30.0 lbs), #8 (25 mm) = 23.5 kg (51.8 lbs). Use the D squared / 162 formula multiplied by the length in meters.
For corrosion resistance, stainless steel grades 304 and 316 are the top choices. Stainless 304 contains 18% chromium and 8% nickel, making it suitable for most environments. Stainless 316 adds molybdenum for superior resistance to saltwater and chemicals. Carbon steel and alloy steel have poor corrosion resistance and require coatings or galvanizing for outdoor or marine use.
This calculator is optimized for steel types only, as the density values and rebar formula are steel-specific. Aluminum has a very different density of about 2,700 kg/m3 — roughly one-third of steel. For other metals, you can apply the same Weight = Volume x Density principle but must use the correct density value for that specific metal.
The D squared / 162 formula is highly accurate for standard carbon steel rebar with a density of 7,850 kg/m3. The constant 162 is derived from 4/(pi x 7.85) x 1000, simplified for field use. Results are within 0.5% of the exact calculation. For stainless steel rebar, which is denser, the formula slightly underestimates weight by about 2%.
Mild steel (carbon steel) contains 0.05-0.25% carbon with a density of 7,850 kg/m3. It is affordable, weldable, and used for general construction. Alloy steel contains additional elements like chromium, molybdenum, or vanadium, giving it higher strength, hardness, and wear resistance at a slightly lower density of 7,750 kg/m3. Alloy steel is used for specialized structural and mechanical applications.
This calculator provides estimates based on nominal dimensions and standard steel densities. Actual weights may vary due to manufacturing tolerances, surface treatments, and alloy composition. Always verify critical calculations with certified engineering data.