Calculate total applied live load from area, uniform load intensity, and a chosen multiplier. The reference live-load reduction equations below are separate and are not applied by this widget.

Area × intensity × your multiplier. This does not check structural capacity, code eligibility or live-load reductions.

1 leaves the entered load unchanged. Use only a multiplier justified for your purpose.

Live Load Formula

The following is a reference floor-live-load reduction equation, illustrated in 2019 Chicago Building Code §1607.11.1. It applies only to eligible members and loads, with KLL × At at least 400 ft². Required minimum fractions are 0.50 for members supporting one floor and 0.40 for members supporting two or more floors; occupancy, heavy-load, garage and other restrictions apply. Roof live loads have separate provisions. Confirm the applicable local code and design requirements.

L = L₀(0.25 + (15) / (√(KLLAₜ)))
  • Where L is the reduced design live load per ft²
  • L0 is the unreduced design live load per ft²
  • KLL is the live load element factor
  • At is the tributary area (ft²)
  • L is typically limited so it does not exceed L0; for KLL × At ≤ 400 ft², no reduction is taken (L = L0).

For an eligible case, multiply the unreduced live-load intensity by the equation’s factor, then enforce the applicable minimum remaining fraction and other code restrictions. The calculator above instead multiplies entered area, intensity and your chosen multiplier; it does not assess reduction eligibility.

The reference code gives a rounded SI coefficient of 4.57 when At is in m², with L and L0 in consistent pressure units such as kPa. Exactly 15 ft is 4.572 m, so the separately rounded SI and customary equations can differ slightly.

L = L₀(0.25 + (4.57) / (√(KLLAₜ)))

Live Load Definition

Live loads arise from use and occupancy, such as people and movable contents, distinct from permanent dead loads. They may be specified as force per area or as concentrated forces. This calculator uses uniform intensity and reports force; lb/ft² in this article means pounds-force per square foot.

Example Problem

How to calculate live load?

First, determine the unreduced live load the structural member is designed for. For this example, the unreduced design live load is 40 lb/ft².

Next, determine the live load element factor. For this example, the element is an interior column that has a KLL of 4.

Next, determine the tributary area. For this problem, the area is found to be 400 square feet (ft²).

For this illustrative eligible interior-column case, the equation gives a remaining fraction of 0.625, above either stated minimum. Using the reference formula:

L = L0 * (0.25 + 15 / SQRT (KLL * At ) )

= 40 * (0.25 + (15/SQRT(4*400)))

= 40 * (0.25 + 0.375)

= 25 lb/ft²