To estimate an RSJ order’s mass, multiply the manufacturer’s kilograms per metre by the full cutting length and number of pieces. For a mixed order, calculate each section and length separately before adding the results.
The table below shares its data with our weight calculator. It covers selected modern UB sections, not every historic RSJ or European section. Match the complete designation before using a row. The final number in a name is nominal: the listed mass of 203×133×25, for example, is 25.1 kg/m.
A mixed order, calculated line by line
This invented schedule demonstrates the arithmetic. The section choices and lengths are not a design for an opening.
| Beam reference | Section | Listed mass | Length per piece | Quantity | Bare-steel mass |
|---|---|---|---|---|---|
| B1 | 203×133×25 UB | 25.1 kg/m | 4.3 m | 2 | 215.86 kg |
| B2 | 254×146×31 UB | 31.1 kg/m | 3.2 m | 1 | 99.52 kg |
| Total | 11.8 m overall | 3 | 315.38 kg |
For B1, 25.1 × 4.3 × 2 = 215.86 kg. For B2, 31.1 × 3.2 = 99.52 kg. Adding the masses gives 315.38 kg, or 0.31538 tonnes.
You cannot multiply the overall 11.8 m length by a single kg/m value because the schedule contains different sections. Nor should you enter 8.6 m as the length for B1 and then enter a quantity of two: that counts the B1 lengths twice. In the calculator, length means length per piece.
Why opening width gives the wrong order weight
Steel extending into a bearing or connection still has mass. Use the issued cutting length rather than a room measurement. Keep a separate line for each length where pieces differ, even when their section designations match.
Before ordering, check that the schedule and fabrication drawing have the same revision. If the drawing changes a section, length or plate arrangement, the earlier total may no longer describe what is being delivered. Record the calculation inputs with the quotation instead of keeping only a screenshot of the final number.
Kilograms, tonnes and kilonewtons
Kilograms and tonnes describe mass. Kilonewtons describe force. In our tools, gravitational force is calculated using 9.81 m/s²:
- 1000 kg = 1 tonne.
- Force in kN = mass in kg × 9.81 ÷ 1000.
- Self-weight in kN/m = listed kg/m × 9.81 ÷ 1000.
For 203×133×25, 25.1 kg/m corresponds to 0.246231 kN/m of bare-beam self-weight. One 4.3 m piece has a mass of 107.93 kg and a total gravitational force of about 1.059 kN. Neither number is the load that the beam is permitted to support.
The distinction matters when using another tool. The load calculator adds beam self-weight to external loads, while the standalone deflection calculator expects it to be included in the entered total. The methodology records which convention each calculator uses.
Why the delivered item may weigh more
The chart describes the steel section. It does not include end plates, splice plates, brackets, bolts, welds, protective finishes or packaging. Manufacturer tolerances and the finished fabrication also limit how closely a theoretical figure can match a measured weight.
Ask the supplier for the complete fabricated weight and delivery arrangement. The calculator does not choose lifting equipment, assess access or establish whether a manual lift is suitable. These decisions need the actual item, site conditions and responsible people’s handling plan.
Do not estimate the I-shaped section as a solid rectangle using its outside depth and width. That counts the empty space between the flanges and gives the wrong volume. Use the tabulated mass for the specified product.
Source and checks before using the table
The section values come from the British Steel UB datasheet. Use the size-chart guide to distinguish nominal labels from actual dimensions. Check family, full designation, grade, cutting length and revision against the supplier’s documents.
Structural work must be designed by a chartered structural engineer and receive the applicable Building Control approval. This mass calculation provides no assessment of structural capacity and has not received an independent engineering review.
Section weights and properties
| Designation | Mass kg/m | Actual depth mm | Actual width mm | Iₓ cm⁴ |
|---|---|---|---|---|
| 152x89x16 | 16 | 152.4 | 88.7 | 834 |
| 178x102x19 | 19 | 177.8 | 101.2 | 1356 |
| 203x102x23 | 23.1 | 203.2 | 101.8 | 2105 |
| 203x133x25 | 25.1 | 203.2 | 133.2 | 2340 |
| 203x133x30 | 30 | 206.8 | 133.9 | 2896 |
| 254x102x25 | 25.2 | 257.2 | 101.9 | 3415 |
| 254x146x31 | 31.1 | 251.4 | 146.1 | 4413 |
| 254x146x37 | 37 | 256 | 146.4 | 5537 |
| 305x127x37 | 37 | 304.4 | 123.4 | 7171 |
| 305x165x40 | 40.3 | 303.4 | 165 | 8503 |
| 305x165x46 | 46.1 | 306.6 | 165.7 | 9899 |
| 356x171x45 | 45 | 351.4 | 171.1 | 12195 |
| 356x171x51 | 51 | 355 | 171.5 | 14265 |
| 406x178x54 | 54.1 | 402.6 | 177.7 | 18893 |
| 457x191x67 | 67.1 | 453.4 | 189.9 | 29597 |
Source: British Steel, Universal Beams datasheet, 21 July 2026, pages 1 and 3. Transcribed 10 October 2026. Values describe the listed modern UB sections, not unidentified historic RSJs. The calculators and this table share the same data.