Estimate a capacity allowance, total load, unity-power-factor current, or maximum whole fixtures using the stated 1.25 arithmetic model.

Apply the stated 1.25 multiplier to equal fixture loads.

1.25 is an arithmetic allowance, not a universal dimmer rule. Check manufacturer load ratings, lamp compatibility, inrush and ganging derating. Use actual lamp watts, not equivalent brightness watts.

Optional settings

Dimmer Wattage Formula

The following formula is used to calculate a dimmer wattage.

DW = F × FW × 1.25
  • Where DW is the dimmer wattage (watts)
  • F is the number of fixtures
  • FW is the wattage of each fixture (watts)

For this model, multiply fixture count by actual fixture watts and then by 1.25. This allowance does not establish a safe or compatible dimmer: check the manufacturer’s load-specific capacity, lamp compatibility, inrush limits and ganging derating. LED/CFL capacity can differ substantially from incandescent capacity.

What is a dimmer wattage?

Definition:

A dimmer’s wattage rating is its permitted capacity for a specified load type and installation. The modeled value here is an arithmetic estimate, not a substitute for that rating or installation instructions.

How to calculate dimmer wattage?

Example Problem:

The following example shows the 1.25 arithmetic model; confirm the actual dimmer rating and compatibility separately.

First, determine the number of fixtures. In this example, there are 10 total fixtures the dimmer will control.

Next, determine the average wattage of those fixtures. For these fixtures, the average wattage is 60 watts.

Finally, calculate the modeled capacity allowance using the formula above:

DW = #F * FW * 1.25

DW = 10* 60 * 1.25

DW = 750 watts