Live load depends entirely on how the space is used — heavier occupancies mean more weight per square foot.
Live load is the variable weight of occupants, furniture, and movable objects — prescribed by code based on occupancy type, not calculated from actual weights.
Unlike dead load, you don't calculate live load — you look it up. ASCE 7 Table 4.3-1 assigns minimum live loads by occupancy: 40 psf for residential, 50 psf for offices, 80 psf for corridors above the first floor, 100 psf for lobbies and assembly areas. These aren't averages — they're conservative upper bounds intended to cover the worst-case loading during the building's life.
ASCE 7 Section 4.7 allows live load reduction when tributary areas are large. The logic: the probability that every square foot of a 5,000 sf floor is simultaneously loaded to 50 psf is very low. The reduction factor depends on the tributary area and the element type. For a column supporting 4 floors of office space, the effective live load might be 30-35% lower than the code minimum. But some loads — assembly and heavy storage — cannot be reduced.