Tributary Area & Load Takedown
Find the floor area a column supports and the load it carries, from your bay spacings and a live-load intensity.
Center-to-center — feet or metric
Center-to-center — feet or metric
400 sf37.2 m²
Tributary area
20.0 kips89 kN
Member load
Interior column (4 bays) · 50 psf live
Assumptions & notes
- Interior column collects one full bay (×1).
- Tributary area = bay X × bay Y × 1.
- Live load only — add dead load and verify against your code (ASCE 7-22 T.4.3-1).
How load takedown works
Every column carries the slab area that drains to it — its tributary area — bounded by the midlines to the neighbouring columns. On a regular grid an interior column collects a quarter of each of its four surrounding bays, which adds up to one full bay; an edge column collects half a bay; a corner column a quarter.
The load that member carries is just tributary area × load intensity.
The presets are minimum live loads from ASCE 7-22 Table 4.3-1 — pick your
occupancy or enter a custom value. Remember this is live load only:
add the dead load (and snow or other loads as applicable) and verify against your
adopted code. It's a takedown estimate, not a structural design.
This is the practical companion to the load-paths idea — loads accumulate down the path, and tributary area is how you size each link.
Official source
Opens the official standard in a new tab — always verify against your adopted code edition and local authority (AHJ).
Frequently asked questions
What is tributary area?
The floor or roof area that drains its load to a single column or beam, bounded by the midlines to the neighboring supports. It's the area that one member is responsible for carrying.
How do I find the load a column carries?
Multiply its tributary area by the load intensity — area in square feet times pounds per square foot. On a regular grid an interior column's tributary area is one full bay, an edge column's is half a bay, and a corner column's is a quarter bay.
What is the difference between interior, edge, and corner columns?
It's how much of the surrounding bays each collects: an interior column gathers a quarter of each of its four bays (one full bay total), an edge column half a bay, and a corner column a quarter bay — so interior columns carry the most.