Steel Weight Calculator for Rods, Sheets & Tubes

Steel weight calculator

A steel weight calculator finds the mass of a piece of steel from its shape and dimensions. It works for three common shapes: solid rods, flat sheets, and hollow tubes. The calculator multiplies the shape's volume by the density of steel, then reports the result in kilograms, grams, and pounds.

Knowing the weight of a piece of steel matters before it is ordered, lifted, or shipped. A shop needs it to price a cut. An engineer needs it to check that a beam does not exceed a structure's design load. A crane operator needs it to confirm the load is within the machine's rated capacity.

Steel weight formula

The general formula is:

$\text{Weight} = \text{Volume} \times \text{Density}$

Density is the mass packed into a given volume of a material. Mild (carbon) steel has a density of 7.85 grams per cubic centimeter (g/cm³). That means one cubic centimeter of mild steel, a cube smaller than a sugar cube, weighs 7.85 grams.

Volume is measured in cubic centimeters (cm³) and depends on the shape. The three shapes below use different volume formulas, so picking the right one matters.

Rod (cylinder) volume formula

A rod is a solid cylinder, such as a round bar or a length of rebar.

$V = \pi \times r^2 \times L$

• V = volume (cm³)
• r = radius of the rod (cm), equal to diameter ÷ 2
• L = length of the rod (cm)

Sheet (flat plate) volume formula

A sheet is a flat rectangular slab, such as plate steel or sheet metal.

$V = L \times W \times T$

• L = length (cm)
• W = width (cm)
• T = thickness (cm)

Tube (hollow cylinder) volume formula

A tube is a pipe with a hollow center. Its volume is the outer cylinder's volume minus the inner (hollow) cylinder's volume.

$V = \pi \times L \times (R_o^2 - R_i^2)$

• L = length (cm)
• R_o = outer radius (cm), equal to outer diameter ÷ 2
• R_i = inner radius (cm), equal to inner diameter ÷ 2

Once the volume is known, weight in kilograms follows from:

$\text{Weight (kg)} = \frac{\text{Volume (cm}^3\text{)} \times 7.85}{1000}$

How to calculate steel weight

1. Identify the shape: rod, sheet, or tube.
2. Measure the required dimensions in centimeters (diameter and length for a rod; length, width, and thickness for a sheet; outer diameter, inner diameter, and length for a tube).
3. Apply the matching volume formula above.
4. Multiply the volume by 7.85 g/cm³ to get the weight in grams, then divide by 1000 for kilograms.

For a tube, the inner diameter must be smaller than the outer diameter. If a tube has a 5 cm outer diameter and 0.3 cm walls, the inner diameter is 5.0 − (2 × 0.3) = 4.4 cm, not 4.7 cm, because the wall exists on both sides of the hole.

Worked examples

Example 1: A steel rod

A rod is 2.5 cm in diameter and 300 cm long.

1. Radius = 2.5 ÷ 2 = 1.25 cm
2. Volume = π × 1.25² × 300 ≈ 1,472.6 cm³
3. Weight = 1,472.6 × 7.85 ÷ 1000 ≈ 11.56 kg

Example 2: A steel sheet

A sheet measures 120 cm long, 80 cm wide, and 0.3 cm thick.

1. Volume = 120 × 80 × 0.3 = 2,880 cm³
2. Weight = 2,880 × 7.85 ÷ 1000 ≈ 22.61 kg

Example 3: A steel tube

A tube has an outer diameter of 4.2 cm, an inner diameter of 3.8 cm, and a length of 250 cm.

1. Outer radius = 2.1 cm; inner radius = 1.9 cm
2. Volume = π × 250 × (2.1² − 1.9²) = π × 250 × 0.8 ≈ 628.3 cm³
3. Weight = 628.3 × 7.85 ÷ 1000 ≈ 4.93 kg

Steel density by type

The 7.85 g/cm³ figure applies to mild (carbon) steel, which is mostly iron with a small amount of carbon. Other steel alloys and metals differ:

To estimate a different metal's weight, multiply the steel result by (that metal's density ÷ 7.85).

Frequently asked questions

Why does a calculated weight differ from a supplier's quoted weight?

Several factors cause small gaps. Steel mills produce bars and sheets within a manufacturing tolerance, so a "10 mm" rod might actually measure 9.8–10.2 mm. Coatings add weight too: hot-dip galvanizing adds roughly 3–5%, and mill scale, the dark oxide layer left by hot rolling, adds roughly 0.5–1%. A calculated weight is usually within 2–3% of a scale weight, which is close enough for quotes and material planning.

Can this formula be used for stainless steel or aluminum?

Yes, by adjusting for density. Multiply the mild-steel result by the ratio of the other metal's density to 7.85. For stainless steel, add about 2%. For aluminum, divide by about 2.9. The density table above gives the adjustment factors for other common metals.

How is rebar weight calculated?

Rebar (reinforcing bar) is calculated the same way as a solid rod, using its nominal diameter. Deformed rebar, which has ribs for grip, weighs about 1–2% more than a smooth rod of the same diameter; this difference is small enough to ignore for most estimates. A 10 mm rebar works out to about 0.62 kg per meter using the rod formula; a 16 mm rebar works out to about 1.58 kg per meter.

How is weight calculated for square or rectangular tubing?

Square and rectangular tubing is not a cylinder, so the rod and tube formulas do not apply directly. Instead, subtract the hollow inner volume from the solid outer volume: outer volume is length × outer width × outer height, and inner volume is length × (outer width − 2 × wall thickness) × (outer height − 2 × wall thickness). For a 100 cm length, 5 cm × 3 cm outer dimensions, and 0.3 cm walls: outer volume is 1,500 cm³, inner volume is 100 × 4.4 × 2.4 = 1,056 cm³, so the steel volume is 444 cm³, giving a weight of about 3.49 kg.

Why does a small measurement error matter so much?

Volume for a rod or tube depends on the radius squared, so a small error in diameter is amplified. A 1 mm error on a 10 cm diameter changes the calculated weight by roughly 2%. Measuring with calipers instead of a tape measure keeps results closer to a scale weight.

References

1. ASTM A6/A6M-19, Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet Piling, ASTM International, 2019.
2. American Institute of Steel Construction, Steel Construction Manual, 15th edition.
3. BS EN 10025-1:2004, Hot rolled products of structural steels — General technical delivery conditions, British Standards Institution.