Free calculator
Steel beam load calculator
Example values: a 4 m beam under a timber first floor and a plastered 100 mm medium-density block wall. Typical UK figures, so change them to suit your job.
m
Floor
Loaded width: half the joist span, added up for each side where joists bear on the beam.
m
kN/m²
kN/m²
Roof
Set the loaded width to 0 if no roof bears on the beam.
m
kN/m²
kN/m²
Wall on the beam and self-weight
m
kN/m²
kN/m
Result
Line load on the beam, gk + qk
8.00 + 5.70 kN/m
Characteristic (gk + qk) UDL
13.70 kN/m
ULS (1.35gk + 1.5qk) UDL
19.35 kN/m
Characteristic (gk + qk) reaction, each end
27.40 kN
gk 16.00 + qk 11.40 kN
ULS (1.35gk + 1.5qk) reaction, each end
38.70 kN
ULS mid-span moment, wL²/8
38.70 kNm
Loads only. This does not choose or check a steel section, its deflection or its bearings.
How it works
Each floor or roof load in kN/m² becomes a line load when you multiply it by the width of floor the beam carries. A wall standing on the beam adds its height times its weight per m². The beam adds its own weight. With the beam simply supported and the load spread evenly along it, each end takes half the total.
Assumptions behind the numbers:
- One span, simply supported, with the load uniform along its whole length. A post, another beam or a wall that stops part way along puts a point load on the beam, which needs a proper analysis.
- L is the effective span, centre to centre of the bearings, not the clear opening.
- The full height of wall on the beam is included, with no arching. That is safe for a beam in a wall. For a lintel in bonded masonry the lintel calculator can take a smaller load.
- Floor and roof imposed loads are both factored by 1.5 and added. The 6.10a and 6.10b pair in the UK National Annex to BS EN 1990 can give a slightly lower ULS figure.
- In US mode the line loads are in plf. ASD is D + L and LRFD is the worse of 1.4D and 1.2D + 1.6L, following ASCE 7-22. Roof live load is treated as L, which errs on the safe side. Snow is not handled separately: enter the larger of roof live load Lr and snow load S.
What it does not do. It does not pick a section or check bending resistance, shear, lateral torsional buckling, deflection, web bearing or the bearing on the wall. Take the ULS moment and reaction to a steel table or design program, and check deflection under the characteristic loads. Then check the bearing with the padstone bearing calculator.
Worked example
A ground floor internal wall is taken out to open up a kitchen. A steel beam with a 4.0 m effective span replaces it. Timber first floor joists span 4.0 m and 3.6 m onto it, so the loaded width is 2.0 + 1.8 = 3.8 m. The floor is 0.8 kN/m² dead and 1.5 kN/m² imposed. A 100 mm medium-density block wall upstairs, plastered both sides at about 1.9 kN/m², stands 2.4 m high on the beam. Dense block would be about 2.4 to 2.6 kN/m², so check what the wall is built from. Allow 0.4 kN/m for the beam. No roof bears on it.
The 38.7 kN ULS reaction is the one to check on the padstone; the padstone calculator starts from this example. The 27.4 kN characteristic reaction travels down the wall to the footing.
FAQ
How do you calculate the load on a steel beam?
Turn each floor and roof load into a line load by multiplying the load per m² by the width of floor or roof the beam carries. Add the weight of any wall standing on the beam (height × weight per m²) and the beam's own weight. That gives the dead and imposed line loads in kN/m. In the UK, the design (ULS) load is 1.35 × dead + 1.5 × imposed.
What is the reaction at each end of a beam with a UDL?
For a simply supported beam with a uniform load w over a span L, each end reaction is wL/2 and the mid-span moment is wL²/8. A 4 m beam carrying 19.35 kN/m at ULS puts 38.7 kN on each bearing and has a 38.7 kNm moment.
Does this calculator size the steel beam?
No. It works out the loads, the end reactions and the mid-span moment. Choosing a section and checking its bending, shear, buckling, deflection and bearings is design work for an engineer, using steel tables or design software.
What span should I use for a beam over an opening?
The effective span, from the centre of one bearing to the centre of the other. For a beam with 150 mm bearings at each end of a 3.6 m opening that is 3.6 + 0.15 = 3.75 m.
Should I use characteristic or ULS loads for a beam?
Use the ULS reaction and moment to design the beam and to check the padstone. Use characteristic loads to check deflection and to carry the reaction down to the foundation for the bearing pressure.
Check the result
Check against the code and get a qualified engineer to sign off.
This calculator gives loads for a quick check or a first pass. It does not design the beam. A real beam has to be checked against BS EN 1993-1-1 (or AISC 360 in the US) by someone qualified to do it, along with its bearings and the walls and foundations below.
Read more: one beam reaction followed from padstone to footing, how loaded width works, characteristic vs design loads and loft conversion steels.