About the Watts to Lumens Calculator
This calculator converts W to lm. W is one joule of energy per second, the basic unit of power printed on bulbs, chargers and appliances, and lm is lumens, the total amount of visible light a lamp gives out. It multiplies the watts by the efficacy of the lamp in lumens per watt. Enter your figures and the answer appears at once, together with a few related values, and you can copy the result with one tap. The sums are done in your browser and nothing is sent anywhere.
Updated October 2026
How to use the Watts to Lumens Calculator
- 1Enter the value in W.
- 2Fill in the other boxes that the W to lm calculation needs, such as time, voltage or power factor.
- 3Read the answer in the large result box.
- 4Check the extra rows for related values.
- 5Press Copy result to keep it.
When you need W to lm
Watts measure the electricity a lamp uses, not the light it gives. Different lamp types turn a watt into very different amounts of light. That is why an LED bulb of 9 W can replace a 60 W incandescent bulb. Lumens are the figure to compare when you shop for light.
Pick the lamp type to use a typical efficacy, or choose I know the efficacy and type the lumens per watt from the packaging. The result is an estimate: actual figures vary between products and fall as lamps age.
How the W to lm sum works
Lumens = watts × luminous efficacy (lumens per watt). A 9 W LED lamp at 100 lm/W gives about 900 lm, similar to an old 60 W incandescent bulb at 14 lm/W.
The displayed answer is rounded to six significant figures, but the sum itself is not rounded, so converting W to lm and back again gives you the number you started with.
- LED: about 100 lm/W
- Halogen: about 20 lm/W
- Incandescent: about 14 lm/W
Mistakes to avoid when converting W to lm
Do not use the watts of an old bulb as a guide to brightness for a new one. Use lumens instead. A room usually needs about 300 to 400 lumens per square metre for general lighting, more for kitchens and workspaces.
On phone and computer
On a phone, type in the boxes one after another and read the lm result underneath; the Copy button puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the lm value move. The W to lm page works the same on both. Go the other way with Lumens to Watts Calculator. Lumens to Lux Calculator and Candela to Lumens Calculator help with room lighting plans, and Electricity Cost Calculator shows what lamps cost to run.
Features
- W to lm in one step
- Related values shown with the answer
- Clear messages for impossible inputs
- Copy the result with one tap
- Private: nothing is uploaded
- Works on phone and computer
Frequently asked questions
How do I convert W to lm?
Lumens = watts × luminous efficacy (lumens per watt). A 9 W LED lamp at 100 lm/W gives about 900 lm, similar to an old 60 W incandescent bulb at 14 lm/W.
What is the formula for W to lm?
Lumens = watts × luminous efficacy (lumens per watt). The calculator applies it exactly and rounds only the displayed answer.
What is the difference between W and lm?
W is one joule of energy per second, the basic unit of power printed on bulbs, chargers and appliances. lm is lumens, the total amount of visible light a lamp gives out. They measure different things, which is why converting from W to lm needs more than a simple multiplication in some cases.
How many lumens is a 60 watt bulb?
An incandescent bulb of 60 W gives about 840 lumens at 14 lm/W. A halogen of 60 W gives about 1,200 lumens.
What is luminous efficacy?
The lumens a lamp produces per watt of electricity. Higher is better: modern LEDs reach 100 lm/W or more.
Is this W to lm calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so the figures you type are not uploaded or stored. It is meant for planning and learning; for wiring or safety work, check the result against your equipment's rating plate and local rules.