Free calculator
Column load calculator
Example values: an office column carrying 30 m² of three concrete floors and a flat roof. Typical UK figures, so change them to suit your job.
Column
m²
no.
kN
Each floor
The same loads at every floor. Include finishes, services and partitions.
kN/m²
kN/m²
Roof
kN/m²
kN/m²
Imposed load reduction
UK National Annex factor αn, on floor imposed load only, never the roof. Check the use allows it.
Result
Load to the foundation, Gk + Qk
578.0 + 198.0 kN
Floor imposed load × 0.80 at the base
Characteristic at the foundation
776.0 kN
ULS (1.35Gk + 1.5Qk) at the foundation
1077.3 kN
The table below runs from the top down. Each row adds that level and the column length beneath it.
Running total, top down (kN)
Scroll the table sideways to see every column.
| Level | Adds Gk | Adds Qk | Factor | Total Gk | Total Qk | Char. | ULS |
|---|---|---|---|---|---|---|---|
| Roof | 122.0 | 18.0 | - | 122.0 | 18.0 | 140.0 | 191.7 |
| Floor 3 | 152.0 | 75.0 | 1.00 | 274.0 | 93.0 | 367.0 | 509.4 |
| Floor 2 | 152.0 | 75.0 | 0.90 | 426.0 | 153.0 | 579.0 | 804.6 |
| Floor 1 | 152.0 | 75.0 | 0.80 | 578.0 | 198.0 | 776.0 | 1077.3 |
| Foundation | 578.0 | 198.0 | 776.0 | 1077.3 |
Factor is the reduction on the floor imposed load carried at that level. Total Qk is the roof imposed load plus the reduced floor imposed load.
How it works
At each level the column picks up the floor over its tributary area, plus its own weight for the storey below. Working down from the roof, each level adds to the total above it, so the bottom row is the load on the foundation. Floor 1 is the lowest suspended floor; a ground bearing slab is not counted.
n is the number of floors carried at that level. The reduction is a toggle: switch it off if the floors are storage, plant or any other use the code does not allow it for.
Assumptions behind the numbers:
- Every floor has the same tributary area and the same loads. A column that picks up a transfer beam, a change of grid or a different use on one floor needs a full takedown.
- Tributary areas are found as if each span is simply supported. A continuous slab or beam puts more load on the first internal column than its area suggests.
- UK reduction uses αn from the UK National Annex to BS EN 1991-1-1, on floor imposed load only. The roof imposed load is added unreduced. The area reduction αA is not applied as well.
- Floor and roof imposed loads are both factored by 1.5 and added, which errs on the safe side against the 6.10a and 6.10b pair in the UK National Annex to BS EN 1990.
- US mode uses the general formula of ASCE 7-22 section 4.7.2: L = L0 (0.25 + 15 / √(KLL × AT)), with AT the floor area carried and KLL from Table 4.7-1, which you pick: 4 for interior columns and exterior columns without cantilever slabs, 3 for edge and 2 for corner columns with cantilever slabs. It is used only when KLL × AT is at least 400 ft² and L0 is no more than 100 psf, and never below 0.5 L0 for one floor or 0.4 L0 for two or more. Roof live load is not reduced. ASD is D + L and LRFD the worse of 1.4D and 1.2D + 1.6L.
- Not all of section 4.7 is covered. ASCE 7-22 allows no reduction in assembly occupancies and limits it in passenger vehicle garages, so switch the reduction off for those. Live loads over 100 psf may be reduced by up to 20% on members carrying two or more floors; this calculator does not reduce them at all, which errs on the safe side. Snow is not handled separately: enter the larger of Lr and S as the roof live load.
Worked example
An internal column in an office on a 6 m × 5 m grid carries 30 m² per floor. It holds up three concrete floors at 5.0 kN/m² dead and 2.5 kN/m² imposed, and a flat roof at 4.0 kN/m² dead and 0.6 kN/m² imposed. Allow 2 kN for the column in each storey.
Without the reduction the floor imposed load stays at 225 kN, so Qk is 243 kN, the characteristic total 821 kN and the ULS total 1,144.8 kN. The reduction saves about 6% at the base here, and more on taller buildings.
Column loads in a tower
The same takedown done for every column in a building, with transfer beams and a column schedule, in 1:40.
FAQ
How do you calculate the load on a column?
Find the column's tributary area, usually half way to the next column in each direction. At each floor, multiply that area by the dead and imposed loads per m², add the column's own weight for the storey below, and keep a running total from the roof down. The total at the bottom is the load on the foundation.
What is imposed load reduction for columns?
Every floor is unlikely to be fully loaded at the same time, so the UK National Annex to BS EN 1991-1-1 lets you reduce the total floor imposed load on a column by a factor αn: 1.0 for one floor, 0.9 for two, 0.8 for three, 0.7 for four, 0.6 for five to ten and 0.5 above ten. It does not apply to the roof or to storage areas.
How do I find a column's tributary area?
On a regular grid, multiply the column spacing in one direction by the spacing in the other: an internal column on a 6 m × 5 m grid carries 30 m² per floor. An edge column carries about half that plus the edge strip and cladding, a corner column about a quarter. A continuous slab puts more than this on the first internal column.
Should I include the column's self-weight?
Yes. It is small for steel, often 1 to 2 kN per storey, but a 300 × 300 mm concrete column 3 m high weighs 0.3 × 0.3 × 3 × 25 = 6.75 kN, which adds up over several storeys.
Which column load total goes to the foundation?
Use the characteristic (unfactored) total to size the pad against the allowable bearing pressure. Use the ULS total to design the column and the reinforcement in the pad.
Check the result
Check against the code and get a qualified engineer to sign off.
This is one column with repeated floors. Check the loads and the reduction against BS EN 1991-1-1 and its UK National Annex, or ASCE 7 in the US, and have a qualified engineer sign off the column and its foundation.
Read more: column design for large structures, a load takedown by hand, characteristic vs design loads and typical UK floor and roof loads.