Steel Weight Calculation: Formulas for Plate, Bar and Pipe

The one number behind every formula

Carbon and low-alloy steels have a density of 7.85 g/cm³ (7850 kg/m³). All theoretical-weight formulas are just volume × 7.85. (Stainless steels run slightly higher, roughly 7.9–8.0; the formulas below are for carbon and alloy steels.)

Plate and sheet

Weight per square metre is the simplest in steel:

kg/m² = thickness (mm) × 7.85

• 10 mm plate: 78.5 kg/m²
• 20 mm plate: 157 kg/m²

Worked example: a 20 mm plate 2000 × 6000 mm has an area of 12 m², so it weighs 12 × 157 = 1884 kg.

Flat bar uses the same logic per metre: kg/m = 0.00785 × width (mm) × thickness (mm). A 60 × 10 mm flat runs 0.00785 × 600 = 4.71 kg/m.

Round bar

kg/m = 0.00617 × d² (d = diameter in mm)

Worked example: Ø50 mm bar → 0.00617 × 2500 = 15.4 kg/m. A 4 m length weighs about 61.7 kg.

Companion factors: square bar kg/m = 0.00785 × a² (40 mm square: 12.56 kg/m); hexagonal bar kg/m = 0.00680 × (across-flats)².

Pipe and tube

kg/m = 0.02466 × (OD − wall) × wall (all dimensions in mm)

Worked example: NPS 6 Sch 40 pipe, 168.3 mm OD × 7.11 mm wall → 0.02466 × (168.3 − 7.11) × 7.11 = 0.02466 × 161.19 × 7.11 ≈ 28.3 kg/m — matching the tabulated 28.26 kg/m for that size.

The pipe formula works because the annulus area equals π × (OD − wall) × wall; the constant 0.02466 is π × 7.85 ÷ 1000.

Angles, channels and beams

For standard sections, skip the geometry: every standard (EN 10365, ASTM A6) publishes a mass per metre for each designation, calculated from the rolled profile including fillets. An IPE 300 beam is listed at 42.2 kg/m — use the table value rather than computing from flange and web dimensions, which would miss the fillets.

Theoretical vs actual weight

Formulas give theoretical weight at nominal dimensions. Real product varies within its tolerance band: a plate at the thick end of EN 10029 class A, or a bar at the top of its tolerance, weighs measurably more. Contracts therefore state whether settlement is on theoretical weight (the usual practice for plate and long products) or on actual weighed weight. When checking a delivery, compare piece counts and a sample weighing against the tolerance band before disputing the invoice.

Quick sanity checks

Three habits catch most estimating errors. First, keep the density straight: every factor above scales linearly, so a stainless part at density ~7.95 weighs about 1.3% more than the carbon-steel figure. Second, convert carefully — 1 kg/m equals 0.672 lb/ft, so a 28.26 kg/m pipe is 18.97 lb/ft in US tables; a factor-of-1.5 mistake in either direction is the classic spreadsheet error. Third, weigh one sample piece from any large delivery: if the sample sits inside the tolerance-implied weight range, the paperwork is almost certainly fine too.