Watts to lumens: how to convert
Watts tell you how much electricity a lamp uses. Lumens tell you how much light it gives. To go from one to the other you multiply by the lamp’s luminous efficacy: lumens = watts × lm/W.
Open the watts to lumens converter
Why there is no single conversion
The theoretical limit is 683 lm/W, for ideal single-colour light at 555 nm. Real white lamps are far below it, and each type differs. Using the example bulbs on this site’s converter: an LED bulb giving about 800 lm at about 9 W is about 89 lm/W, and a 60 W incandescent bulb giving about 800 lm is about 13 lm/W. These are examples from the cited sources, not a guarantee for any particular product: use the lumens and watts printed on your bulb’s packaging or datasheet.
Next steps
- Battery runtime calculator: use the watts your lights draw to estimate hours on a battery.
- LED strip power supply calculator: size a power supply from strip watts and length.
- Room lux calculator: find the total lumens a room needs.
Frequently asked questions
Can I convert watts to lumens with one number?
No. Watts measure the electrical power a lamp uses; lumens measure the light it gives out. The link between them is luminous efficacy in lm/W, which differs by lamp type, so the same wattage gives different lumens on an LED and an incandescent bulb.
What is 683 lm/W?
It is the theoretical maximum luminous efficacy, reached only by ideal monochromatic light at 555 nm. No real white light source reaches it.
Where is the converter?
The lumens to watts calculator converts in both directions with the efficacy values and sources shown.