EngineeringFormulaCivil & Structural Engineering
Steel Weight Calculator
Calculate the weight of steel round bar, square bar, flat bar/plate, or round tube.
Ordering or shipping steel stock? This calculator turns a bar or tube's cross-section and length into its weight - the number you need for freight quotes, crane/lifting capacity checks, or per-kilogram material cost. Choose round bar, square bar, rectangular bar/plate, or round tube, enter its dimensions, and get an instant weight using standard mild steel density (or your own, for other metals or alloys).
Dimensions
D · Bar diameter
L · Piece length
Material & Pricing
ρ (kg/m³) · Defaults to 7,850 (mild steel)
$/kg · Leave blank to skip cost estimate
Solution
Enter shape dimensions to calculate steel weight.
Weight (round bar) = π × (D / 2)² × L × ρ
Formula Sheet
- mSteel Weight
- DDiameter
- tWall Thickness
- sSide
- WdWidth
- TThickness
- LLength
- ρDensity
Variables & Units
| Symbol | Variable | Description | Common Units |
|---|---|---|---|
| m | Steel Weight | Total weight of the piece. | |
| D | Diameter | Round bar diameter, or round tube outer diameter. | mm, in |
| t | Wall Thickness | Round tube wall thickness. | mm, in |
| s | Side | Square bar side length. | mm, in |
| Wd | Width | Rectangular bar/plate width. | mm, in |
| T | Thickness | Rectangular bar/plate thickness. | mm, in |
| L | Length | Length of the piece. | m, ft |
| ρ | Density | Material density - 7,850 kg/m³ for mild/carbon steel by default. |
How to Use This Calculator
- 01Choose a shape: Round Bar, Square Bar, Rectangular Bar/Plate, or Round Tube (pipe).
- 02Enter the cross-section dimensions for that shape (diameter, side, or width/thickness), and the piece's length.
- 03Density defaults to 7,850 kg/m³ (standard mild/carbon steel) - change it for stainless, aluminum, or another metal using the reference table below.
- 04Optionally enter a price per kilogram for a cost estimate.
- 05For tube or pipe, use actual outside diameter and wall thickness from the mill table or measurement; nominal pipe size alone is not enough for an accurate geometry calculation.
- 06The calculator instantly shows weight, and cost if a price was entered.
How the Formula Works
Every shape reduces to the same underlying formula - weight = cross-sectional area × length × density - with only the cross-sectional area formula changing by shape: a circle (π × radius²) for round bar, a square (side²) for square bar, a rectangle (width × thickness) for rectangular bar/plate, and a ring (outer circle minus inner circle) for round tube.
Round tube's area subtracts the hollow bore from the outer circle: the inner radius is the outer radius minus the wall thickness, so a thicker wall (relative to the outer diameter) leaves less bore and more steel.
Density is the material property that actually distinguishes steel from any other metal in this formula - mild/carbon steel's 7,850 kg/m³ is the default, but the same geometry formulas work for any metal once its density is substituted in.
This is a straight geometric weight calculation, not a structural capacity check - it tells you how much the piece weighs, not whether a given bar or tube size is strong enough for a load.
Worked Example 01
25mm round bar, 6m length
Known
- Diameter (D): 25 mm
- Length (L): 6 m
- Density (ρ): 7,850 kg/m³ (mild steel)
Formula
Weight (round bar) = π × (D / 2)² × L × ρ
Substitution
Weight = π×(0.0125)²×6×7,850
Result
≈23.1 kg
A 25mm diameter round bar, 6 meters long, weighs about 23.1 kg at standard mild steel density - matching the mill-published rule of thumb that a round bar's weight per meter, in kg, is roughly its diameter in mm squared, divided by 162.28.
Worked Example 02
50mm OD round tube, 3mm wall, 2m length
Known
- Diameter (D): 50 mm (outer)
- Wall Thickness (t): 3 mm
- Length (L): 2 m
- Density (ρ): 7,850 kg/m³ (mild steel)
Formula
Weight (round tube) = π × [(D/2)² − (D/2 − t)²] × L × ρ
Substitution
Inner D = 50 − 2×3 = 44 mm, Weight = π×(0.025² − 0.022²)×2×7,850
Result
≈6.96 kg
A 50mm outer diameter round tube with a 3mm wall (44mm bore), 2 meters long, weighs about 6.96 kg - noticeably less than a solid 50mm round bar of the same length, since most of the tube's cross-section is hollow.
Applications
- 01Estimating shipping/freight weight for steel bar or tube stock before ordering
- 02Checking piece weight against crane, hoist, or lifting equipment capacity before a lift
- 03Quick material cost estimates from a price-per-kilogram quote
Common Metal Densities
| Material | Density (kg/m³) |
|---|---|
| Mild / Carbon Steel | 7,850 |
| Stainless Steel (304/316) | 8,000 |
| Cast Iron | 7,300 |
| Aluminum | 2,700 |
| Copper | 8,900 |
| Brass | 8,500 |
Assumptions
- 01The piece is a single uniform length of one shape and one material - a fabricated assembly of multiple pieces should be calculated per piece and summed.
- 02Density is entered as a single figure for the whole piece - it does not account for coatings, platings, or surface treatments, which add a small amount of additional weight not captured here.
- 03This is a solid-geometry weight calculation with no allowance for mill tolerance (real bar/tube stock runs slightly over or under its nominal size) - for a precise shipping or billing weight, use the mill's actual measured dimensions or its published weight-per-length table.
Where This Model Stops
- 01Does not cover structural shapes with non-uniform cross-sections - I-beams, channels, and angles - since those need each mill's actual published section dimensions (web/flange thickness, fillet radii), not a simple geometric formula.
- 02Does not check structural capacity - this calculates weight only, not whether a given bar or tube size can safely carry a load or span.
- 03Assumes a constant cross-section along the full length - a tapered or machined piece needs to be broken into constant-section segments and calculated separately.
- 04Does not include galvanizing, paint, moisture, packing, pallets, or bundle hardware that can affect shipping or invoice weight.
References
- [1]
How to Calculate Steel Weight: Formulas for Plate, Bar, Tube & More
Ram Steelco
Reference for the per-shape volume formulas and the standard mild steel density figure (7,850 kg/m³ / 0.2836 lb/in³) used throughout this calculator.
- [2]
Weight Formula for Steel – Bars, Plates, Pipes & Beams
Solitaire Overseas
Cross-reference for the same shape formulas and density figure, plus the simplified round-bar kg/m rule (D² / 162.28) used to cross-check this calculator's round bar example.
Frequently Asked Questions
Why does this calculator default to 7,850 kg/m³?
That's the standard density figure for mild/carbon steel, the most common structural and fabrication steel and the default assumption behind most published steel weight tables and mill charts. Stainless steel, aluminum, and other metals have different densities - use the reference table below and enter the correct figure for your material.
How much lighter is tube than solid bar of the same outer size?
It depends entirely on the wall thickness relative to the diameter - a thin-wall tube can weigh a fraction of an equivalent solid bar, while a thick-wall tube approaches solid-bar weight as the bore shrinks toward zero. Run both shapes through this calculator with the same outer diameter and length to compare directly.
Does this account for real mill tolerances?
No - this calculates the theoretical weight from the nominal (specified) dimensions. Actual bar and tube stock runs slightly over or under nominal size depending on the mill and manufacturing process, which is why precise shipping or billing weights should come from the mill's own measured dimensions or published weight-per-length table, not a geometry calculation alone.
Can I use this for other metals, not just steel?
Yes - the geometry formulas are the same for any metal. Just replace the density with the correct value for your material (aluminum, copper, brass, cast iron, etc. are all in the reference table below), and the weight calculation is accurate for that metal instead of steel.
Is this exact enough for billing or shipping?
It is a theoretical estimate from dimensions and density. For final billing, crane planning, or freight documentation, use the supplier's certified weight, measured dimensions, or mill-published weight-per-length table.