Estimate a bulb's light output in lumens from its wattage and its technology's luminous efficacy.
How to Use the Watts to Lumens Calculator
Enter the bulb's power draw in watts and a luminous efficacy in lumens per watt, using the table below as a starting point for the bulb's technology, then read the estimated light output in lumens.
Nobody shopping for an LED replacement actually wants watts — they want however many lumens their old bulb used to put out. That's the whole reason bulb packaging switched from advertising wattage to advertising lumens: watts measures power consumed, not light produced, and once LEDs made those two numbers wildly different per bulb, wattage stopped being a useful brightness proxy.
lm = W × efficacy (lm/W)A 60-watt incandescent, the classic "normal" household bulb, produces roughly 800 lumens — filament bulbs convert power to light at only around 14 lm/W, with most of the input energy going to heat instead. An LED hitting that same 800 lumens at 100 lm/W needs just 8 watts. Same brightness, an eighth of the power.
- Incandescent: ~14 lm/W
- Halogen: ~20 lm/W
- CFL: ~60 lm/W
- LED: ~100 lm/W, though this varies by product — check the actual datasheet when it matters
These are typical figures, not a guarantee for any specific bulb — two LED products can differ by 30% or more depending on driver efficiency and chip quality, so treat the table as a starting point for comparison rather than a substitute for the lumen rating printed on whatever you're actually buying. It's also why comparing two bulbs by wattage alone stopped making sense somewhere around 2010 — the number that used to correlate reliably with brightness now mostly tells you about the technology inside, not the light coming out.