Use the free tool below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What Kelvin and mireds actually describe
Colour temperature describes the colour of light, not its heat. It is measured in Kelvin, and the scale runs from warm orange light at low numbers to cool blue light at high numbers. A candle flame sits near 1800 Kelvin, a tungsten household lamp near 3200, midday daylight near 5500, and open shade under a blue sky near 7500 or higher. Cameras and films use these numbers to set white balance, which is the correction that makes a white sheet of paper look white under any light instead of orange or blue.
Mireds measure the same thing on a different scale, and they exist because the Kelvin scale is misleading for filters. A change of 500 Kelvin near 3000 Kelvin shifts colour a lot, but the same 500 Kelvin change near 9000 Kelvin barely shifts it at all. Mireds fix that problem. One mired equals one million divided by the Kelvin value, so equal steps in mireds give equal looking colour shifts anywhere on the scale. That is why filter makers label colour correction filters in mired shift, not in Kelvin: a filter rated at plus 50 mireds warms the light by the same visible amount whether you start from tungsten or daylight.
How to use this Kelvin to mired converter
Type a Kelvin value and the tool shows its mired value at once. For example, 3200 Kelvin equals 312.5 mireds, and 5600 Kelvin equals about 178.6 mireds. Enter a second Kelvin value and the tool shows the mired shift between them, which tells you roughly how strong a correction filter you need. In this example, the shift from 3200 to 5600 Kelvin is about 134 mireds, a large correction that explains why shooting daylight film under tungsten light without a filter turns everything orange. You can also work backwards: type a mired value and the tool converts it to Kelvin, which helps when a filter or a light meter gives you mireds and your camera wants Kelvin.
Photographers meet mireds in three places. The first is colour correction filters, which carry ratings like 81A or 85B, each with a known mired shift. The second is some light meters and studio flash systems, which report colour temperature shifts in mireds because the steps feel even. The third is old film data sheets, which often state a film’s native balance in Kelvin and the filter needed for other lights in mired shift. Even if your camera only shows Kelvin, knowing mireds helps you judge whether a change matters: a 200 Kelvin change at tungsten is a big deal, while the same change at daylight is minor, and mireds make that difference obvious.
Choosing white balance with both scales in mind
For everyday shooting, set white balance to match your main light: tungsten for indoor lamps, daylight for sun, shade for open shade, and cloudy for overcast skies. Auto white balance handles most mixed scenes well, but it struggles when one strong colour dominates, such as a room full of orange walls, and then a manual Kelvin setting gives you control. Start from the numbers in this article, take a test shot of something white or grey, and adjust in steps of about 200 Kelvin at the warm end or 500 at the cool end until white looks white. If you are mixing lights, for example daylight through a window plus tungsten lamps inside, no single setting is perfect, so pick the light on your subject and let the other light go warm or cool as a creative choice.
Two cautions will save you frustration. First, colour temperature is an estimate for most real lights, because cheap LEDs and fluorescent tubes often have a green or magenta tint that Kelvin alone cannot describe; that tint needs a separate green magenta correction. Second, mired shift is a guide for filter strength, not a promise, because filters also absorb light and shift exposure, so test with your actual filter and light before an important shoot. Use this converter to translate between the two scales quickly, keep a note of the Kelvin and mired values that work for your usual lights, and white balance stops being a mystery and becomes one more setting you set with intent.
Related calculators
- Spanish version
- Panning Shutter Speed Calculator – Tracking Speeds for a Sharp Subject on a Streaked Background
- Megapixels to Print Size Calculator – Largest Print from Your Camera Resolution