Watts to Lumens Calculator

Convert power to light output using luminous efficacy.

How the Math Works

The Watts to Lumens Calculator uses the fundamental relationship between power consumption and light output. By multiplying the wattage (W) of a lighting source by its luminous efficacy (lm/W), you determine the total luminous flux in lumens. This formula, lumens = watts × efficacy, quantifies how efficiently a bulb converts electrical energy into visible light, with higher efficacy values indicating more light output per watt consumed.

Practical Applications

To apply this calculation, first identify the wattage of your lighting fixture and determine the efficacy rating of the bulb technology you're considering. For example, an LED bulb with 10 watts and an efficacy of 100 lm/W produces 1,000 lumens of brightness. This allows you to compare different lighting options—such as choosing between a 15W LED (1,500 lumens) and a 60W incandescent bulb (840 lumens)—to achieve the same brightness with greater energy efficiency.

Day-to-Day Use

This calculation empowers everyday lighting decisions, helping you select bulbs that balance brightness, energy use, and cost. By understanding how many lumens you need for specific tasks—like reading (500+ lumens) or ambient room lighting (1,000–2,000 lumens)—you can avoid overpaying for excessive wattage or settling for inadequate illumination. It also supports energy-saving goals by enabling smarter choices that reduce electricity bills and environmental impact.

Worked example

10 W LED at 80 lm/W → 800 lm.

FAQ