How to use the section properties calculator

1. What the calculator does

The section properties calculator works out the geometric properties of a cross-section: area, centroid, second moments of area, radii of gyration, elastic and plastic moduli, torsion and warping constants, shear centre, shear areas, perimeter and mass. Shapes: rectangle, I or H, RHS, CHS, T, channel, angle, a general polygon or built-up section, or a section from the library (UB, UC, IPE and others).

There is no design code: the page badge says it is geometry only, from the STATIX section engine and section library. The one code item is the section class for steel, read from EN 1993-1-1 Table 5.2 for the yield strength you give.

2. The inputs, group by group

3. How to read the result

The properties table lists each property with its symbol, value and unit. z is the strong (major) axis and y the weak (minor) axis; the badge at the top says which axis is stronger and by how much (here I_z/I_y = 2.8).

What to look for: the elastic modulus W_el for stresses in the elastic range, the plastic modulus W_pl for the plastic moment of a class 1 or 2 section, the radius of gyration r for buckling, and the torsion constant J and warping constant C_w for lateral-torsional buckling. For an open section such as a channel, the shear centre is outside the web: a load through the web also twists it. This page has no pass or fail: there is nothing NOT CHECKED, because nothing is checked against a code.

4. Calc sheet and comparison

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The section comparison puts every section of the project side by side: area, I, Z, r and mass per metre. Use “+ Add section” to compare a few profiles.

5. A 2-minute walk-through

1. Open the calculator: a solid 300 × 500 rectangle in steel.
2. Read I_z (3.125 × 10⁹ mm⁴) and check it by hand: bh³/12 = 300 × 500³/12.
3. Change the shape to an I section and see the plastic modulus and the class.
4. Pick a UB from the library and compare it with your own I section.
5. Add a second section and read the comparison.

6. Common mistakes

• Mixing up the axes. On this page z is the strong axis and y the weak one; other books use x and y.
• W_pl for a slender section. The plastic modulus only applies to class 1 and 2 sections.
• Polar moment as the torsion constant. For open sections J is much smaller than I_y + I_z.
• Steel density for a concrete or timber section. Set the density for the mass.
• A built-up section treated as one. Two members act as one section only if they are connected well enough along their length.

7. Where it fits

Use it to check a section before you design with it in the steel member, timber beam or cold-formed calculators, to get the properties of a shape that is not in the tables (a built-up girder, a plate with stiffeners, a concrete T-beam), or to compare candidate profiles by mass before you choose one.

8. Learn more

• Steel Design 1, lesson 2: compression and lesson 3: beams
• Guide: the steel member calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.