The RSJ weight calculator answers a purchasing question: what is the theoretical mass of the selected bare-steel pieces? It multiplies the manufacturer’s mass per metre by length per piece and quantity. It also expresses the resulting gravitational force in kilonewtons.
The result does not tell you how much load a beam can support, how many people can carry it or what lifting equipment to use. Those questions need different information and checks.
Enter one group of identical pieces
Choose the exact UB designation from the issued schedule. Enter the full cutting length in metres and a whole-number quantity. If the pieces differ in section or length, calculate each group separately.
For two pieces of 203×133×25, each 4.3 m long, enter 4.3 as the length and 2 as the quantity. Do not enter the combined 8.6 m length with a quantity of 2. That would count four pieces’ worth of steel.
The expected bare-steel mass is 25.1 × 4.3 × 2 = 215.86 kg. A displayed result of 215.9 kg is the same figure rounded to one decimal place. Keep the original values with the quotation if you need to reconcile totals later.
Check a mixed order separately
Add a third beam, a 3.2 m piece of 254×146×31. It belongs in another calculation: 31.1 × 3.2 × 1 = 99.52 kg. The combined theoretical mass is 315.38 kg.
| Calculation group | Length entered | Quantity entered | Unrounded mass |
|---|---|---|---|
| 203×133×25 UB | 4.3 m | 2 | 215.86 kg |
| 254×146×31 UB | 3.2 m | 1 | 99.52 kg |
| Sum | 315.38 kg |
These are invented order quantities for checking the arithmetic. The sections have not been selected for a real project. The full weight-per-metre chart shows the shared source data and explains mixed schedules in more detail.
Understand the other outputs
One tonne is 1000 kg. To convert mass to gravitational force, the tool multiplies kilograms by 9.81 and divides by 1000. For the two 4.3 m pieces above, the total force is approximately 2.118 kN.
The selected section’s self-weight per metre is a different output: 25.1 × 9.81 ÷ 1000 = 0.246231 kN/m. Keep the “per metre” unit. Entering the total force as a line load would change the calculation.
When moving to our other tools, check their input convention. The beam comparison and load tools add the selected beam’s self-weight. The standalone deflection tool expects a total line load that already includes it. These conventions are documented in the calculation method.
If your result differs from a supplier’s figure
First compare the designation, quantity and cutting length. The last number in the designation is nominal, so it may differ slightly from the manufacturer’s listed kg/m. Check the supplier’s actual product and source table rather than assuming every similar name has identical properties.
Next ask what the supplier’s total includes. End plates, splice plates, brackets, bolts, welds, coatings and packaging are outside this calculator. The table also cannot measure the final fabricated item. A supplier’s complete fabricated weight may therefore be more appropriate for transport and handling planning.
If the section is absent from the dropdown, do not select a nearby size as a substitute. Use the correct manufacturer’s data and a separate calculation, or ask the supplier for the information.
Source: British Steel UB dimensions and properties. Structural work must be designed by a chartered structural engineer and receive the applicable Building Control approval. The calculator provides estimates only and does not select a lifting method or establish structural suitability.