Watts to Lumens Calculator

Find out the lumens equivalent of watts for your lighting with our calculator. Essential for lighting designers and energy savers.

Enter power in watts:
Enter light source:
Or enter luminous efficacy in lumens per watt:
Luminous flux result in lumens:

How It Works

At the core of the Watts to Lumens Calculator is a simple equation:

Φv(lm) = P(W)×η(lm/W)

Here's a breakdown:

This equation forms the basis for translating electrical power into visible light output, providing insights into the brightness you can expect from a specific amount of power.

Lumens to Watts Calculator

Using the Calculator

  1. Enter Power: Input the power of your light source in watts.

  2. Luminous Efficacy: Specify the luminous efficacy, usually in lumens per watt (lm/W).

  3. Get Luminous Flux: The calculator will display the brightness in lumens based on your inputs.

This process allows you to understand how much light a specific amount of power will produce.

Manual Wattage Calculation

Sometimes, manual calculations are necessary, especially for low-wattage LEDs. The formula is:


This equation helps you determine the power your light source needs to achieve a specific brightness.

Finding Luminous Efficacy

To find the luminous efficacy of a bulb when you know its power and luminous flux, you can rearrange the formula:


This equation allows you to assess how efficiently a light bulb converts power into visible light.

Frequently Asked Questions

Multiply the voltage by the amperes (current): Watts = Volts × Amps. Or,

divide lumens by luminous efficacy: Luminous Efficacy = Lumens/Watts

Know the luminous efficacy of the bulb and use the formula:

Luminous Flux (lm) = Power (W) × Luminous Efficacy (lm/W). For example, if a 500-watt bulb has 40 lumens per watt, it gives 20,000 lumens.

LEDs are way more energy-efficient. They use 7 to 10 times less power for the same brightness. Calculate LED wattage with Watts = Lumens / Luminous Efficacy

Bulb light color is measured in Kelvin (K). Lower values are warm and yellowish, higher values are cool and bluish. Normal lighting ranges from 2700 K to 4100 K.