What the LED Wattage Calculator actually calculates
Total watts are lumens divided by efficacy, rounded upward to a whole watt. That rounded total is divided equally among fixtures, so per-fixture watts can remain fractional. It does not choose stock lamp wattages, model differing fixture efficiencies, or assess circuit loading and dimmer compatibility.
The calculation path
Required lumens are divided by lumens per watt and rounded up for purchasing.
Inputs that can change the answer
- Required lumens: Enter required lumens in lm.
- LED efficacy: Rated lumens per watt for the actual lamp or fitting.
- Number of fixtures: Enter number of fixtures as a number; use the definition in the calculation method.
Checks that stay outside the formula
Compare delivered lumens, color temperature, CRI, and dimmer compatibility—not wattage alone.
A practical order for entering the data
- Enter the total lumen output required from the planned lighting.
- Use the selected LED product's efficacy in lumens per watt.
- Enter a whole fixture count and compare the average watts per fixture with available products and their lumen ratings.
Project walkthrough: Lighting: from lumen estimate to fixture layout
Engine check using the prefilled sample
Lighting example: required lumens = 3000 lm, led efficacy = 90 lm/W and number of fixtures = 4. Treat these as demonstration room and fixture values, then recalculate with the dimensions and rated output of the fittings you are considering.
Results for these inputs
- Total LED wattage
- 34 W
- Wattage per fixture
- 8.50 W