Watts to Lumens Calculator

What does this mean?
Convert between watts and lumens for incandescent bulbs, halogen bulbs, CFL and LED.

Disclaimer: Whilst every effort has been made in building this calculator, we are not to be held liable for any damages or monetary losses arising out of or in connection with the use of it. This tool is here purely as a service to you, please use it at your own risk. Full disclaimer. Do not use calculations for anything where loss of life, money, property, etc could result from inaccurate calculations.

Watts and lumens

Most of us are familiar with the power ratings associated with lightbulbs measured in watts (25 watts, 40 watts and 100 watts are common examples). The watt is a unit of power. By contrast, the lumen is a unit of brightness, a measure of the total quantity of visible light emitted by a light source.

Lumens versus watts

Modern energy-efficient bulbs use much less power (wattage) when compared to their incandescent and fluorescent counterparts. As low-wattage bulbs become more commonplace, we need a better way of measuring their output. This is where the lumen comes in. Figures for lumens appear on the packaging of all light bulbs and allow us to compare the brightness (or dimness) of a bulb.

Let's imagine that you are looking for an extremely bright bulb that emits 1,300 lumens. For an LED bulb, producing 1,300 lumens will require around 15 watts of power. However, for a less-efficient halogen bulb, over 60 watts of power are likely to be required to produce the same brightness. Same level of brightness, different amount of power required to produce it.

As you'll see from this example, if you're looking to replace your old incandescent or halogen bulbs with more energy-efficient ones (CFL, LED), being able to cross-reference lumen figures will help you pick the right bulb.

Converting watts to lumens

Converting watts to lumens requires the following formula:

lumens = watts × (lumens per watt)

How many lumens do I need?

More lumens means more light. So, if you previously bought incandescent bulbs measured in watts, here's a handy guide showing how many lumens you might need and the wattage conversion. Note that these conversions use a set average figure for lumens per watt (lm/W), based upon data from the Energy Saving Trust and Energy Star. Actual light efficiency and output will vary by product. So, you're recommended to check the 'lighting facts' label on the bulb packaging before purchase.

Watts to lumens chart
Incandescent bulb
(12-18 lm/W)
LED bulb
(90 lm/W)
(23 lm/W)
25 W300-450 lm3-5 W 15-22 W
40 W480-720 lm5-8 W 23-35W
60 W720-1080 lm8-12 W35-52 W
75 W900-1350 lm10-15 W44-65 W
100 W1200-1800 lm14-20 W58-87 W
Conversions are a guide only. Bulb efficiency may vary.

If you're considering replacing your existing light bulbs with more energy-effiicient LED bulbs, take a look at our LED Savings Calculator to see the possible savings.

If you have any problems using this watts to lumens converter, please contact me.