About the Candela to Lumens Calculator
Candela and lumens both describe light, but not in the same way. Lumens measure the total light a source gives out, while candela measure how strongly the light shines in one direction. A narrow beam concentrates its lumens into a small cone, giving a high candela value, and a wide beam spreads the same lumens out. This calculator converts between the two using the beam angle: it works out the solid angle of the cone in steradians, then multiplies or divides. It is useful for spotlights, torches, bike lights, stage lights and the spot LEDs on product data sheets.
Updated October 2026
How to use the Candela to Lumens Calculator
- 1Choose candela to lumens, or lumens to candela.
- 2Enter the luminous intensity or the luminous flux.
- 3Enter the full beam angle of the light in degrees.
- 4Read the converted value and the solid angle of the beam.
- 5Try a different angle to see how a wider beam lowers the candela.
Example calculations
A torch rated 10,000 candela with a 10 degree beam puts out about 76 lumens, since the solid angle is only 0.0239 steradians. A flood light of 800 lumens over a 120 degree beam has an intensity of about 127 candela. A 1,000 lumen lamp spread over 360 degrees gives 79.6 candela.
These numbers show why a narrow beam looks much brighter in the middle than a wide one, even with the same lumens.
When you compare products, check whether the candela value is the peak at the centre of the beam or an average. Many torch specifications quote peak beam intensity, which can be several times higher than the average over the cone, so the lumens you calculate from it will overstate the real output. A lumens figure measured in an integrating sphere is usually the better number for total light, and candela is the better one for how far the beam reaches.
Typical beam angles
- Narrow spot: 10 to 15 degrees.
- Spot: 24 to 36 degrees.
- Flood: 60 to 90 degrees.
- Wide flood: 100 to 120 degrees.
- Bare omnidirectional bulb: close to 360 degrees.
Related lighting tools
The Lumens to Watts Calculator shows how much power a given brightness needs, the Lumens and Lux Calculator relates light to surface area and the Unit Converter handles lengths and areas. Together they cover most lighting design sums for homes and small projects. To get the room's brightness, continue with the Lumens to Lux Calculator, and use the Lux to Watts Calculator for the power draw.
Features
- Both directions of conversion
- Solid angle in steradians shown
- Works for any beam angle up to 360 degrees
- Handles spotlights and floodlights
- Clear error messages
- Private, free and instant
Frequently asked questions
What is the formula for candela to lumens?
Lumens equal candela times the solid angle of the beam in steradians. The solid angle of a cone with full angle θ is 2π times (1 − cos(θ/2)). A 1,000 candela beam of 30 degrees gives about 214 lumens.
What is a candela?
The candela is the SI unit of luminous intensity, the brightness of a light in a particular direction. One candela is roughly the intensity of a common candle, which is where the name comes from.
What is a steradian?
A steradian is the unit of solid angle, a measure of how much of the space around a point a cone takes up. A full sphere is 4π steradians, about 12.57, and a hemisphere is 2π.
Why do lumens go down when the beam gets narrower?
They don't, for a given lamp. A lamp of fixed lumens makes more candela as its beam narrows. For a fixed candela, however, a narrower beam means fewer total lumens, since the intensity is only shining over a small cone.
Is the calculation exact for real lights?
It assumes an even beam. Real lamps are brighter in the centre and fade at the edge, and manufacturers define the beam angle as the point where the intensity falls to half. The result is a good estimate, not a measurement.
When is a bare bulb 360 degrees?
A bulb that shines in all directions equally is an isotropic source with a solid angle of 4π. Real bulbs are blocked by their base, so they cover a little less. Use 300 to 360 degrees as an approximation.