Lumens to watts calculator

Why there is no fixed conversion

Lumens are the light coming out and watts are the power going in, so there is no conversion between them the way there is between metres and feet. What links the two is luminous efficacy, measured in lumens per watt, and that is a property of the individual lamp rather than a constant. Once you pick the technology you can estimate it: watts = lumens ÷ lm/W. That is what the calculator above does.

Efficacy by light source

• Incandescent: 15 lm/W
• Halogen: 18 lm/W
• CFL: 60 lm/W
• Fluorescent tube: 80 lm/W
• LED: 90 lm/W

Those are the figures the calculator works from, based on what sells today. Incandescent and halogen sit at the top of their real ranges, and are on the way out of Australian shops anyway, so treat those two rows as what you are replacing rather than what you would buy. 90 lm/W is a good current LED rather than a market average: mainstream product runs roughly 60 to 120 lm/W, and premium lamps go higher again.

So 800 lm takes about 53 W from an incandescent lamp and about 9 W from an LED, the same light for a sixth of the power.

Old bulb sizes in lumens

Most people still think in bulb sizes, where "60 W" describes a brightness rather than a power draw. These are the figures LED and CFL equivalents are designed to hit:

• 40 W: about 450 lm
• 60 W: about 800 lm
• 75 W: about 1,100 lm
• 100 W: about 1,600 lm

They are a labelling convention, not a measurement. Anything from roughly 750 to 1,050 lm gets sold as a 60 W equivalent, so read the lumen figure on the box.

Most LED lamps made or imported from March 2026 have to declare their rated efficacy on the packaging, so you can read the lm/W off the box instead of dividing. Stock that was already here can still be sold without it, so expect to see both for a while. Efficiency is not the only number that matters either: colour temperature changes how the same lumens feel, and for downlights the GU10 or MR16 base decides what you can fit.