RGB to color temperature

This RGB to color temperature calculator takes three sRGB channel intensities—red, green, and blue—each as an integer from zero through two hundred fifty-five, and estimates the correlated color temperature (CCT) in kelvin using a deterministic path through CIE XYZ, chromaticity coordinates, and McCamy's classic cubic approximation. Photographers, lighting designers, UI engineers, and students use this mapping when a screen color must be compared to a blackbody or daylight temperature band, when a palette note needs a single kelvin tag, or when homework asks for CCT from an RGB triple without a spectrophotometer. The engine inverse-compands each channel, multiplies by the D65 sRGB-to-XYZ matrix, forms x and y chromaticity, then evaluates McCamy's polynomial—never calling the network, sampling randomness, or depending on the clock.

What a kelvin value from RGB tells you

In the eight-bit sRGB model used by CSS and most web graphics, each of red, green, and blue is an integer channel from zero through two hundred fifty-five. Correlated color temperature asks a different question: roughly how warm or cool a stimulus looks along a blackbody-like scale measured in kelvin. This tool does not reverse-engineer a unique spectral power distribution—many spectra can share similar chromaticity—but it estimates CCT from the color's CIE 1931 chromaticity using McCamy's published cubic formula, which is widely used as a fast closed-form approximation.

Conversion first scales each channel by dividing by two hundred fifty-five, then undoes sRGB gamma so the values become linear light. Those linear channels pass through a fixed three-by-three matrix into CIE XYZ under illuminant D65. Chromaticity follows as x equals X over the sum of X, Y, and Z, and y equals Y over that same sum.

McCamy then forms n equals (x minus zero point three three two zero) divided by (zero point one eight five eight minus y), and CCT equals four hundred forty-nine n cubed plus three thousand five hundred twenty-five n squared plus six thousand eight hundred twenty-three point three n plus five thousand five hundred twenty point three three, in kelvin. There is no path that accepts percentages or floating-point channels as input, and no silent clamp of two hundred fifty-six down to two hundred fifty-five.

How r, g, and b are read and how Kelvin stays reproducible

Outer whitespace on string channels is trimmed; an optional leading plus is allowed only when the remaining characters are decimal digits that parse to an integer in range. A bare JavaScript number is accepted only when it is a finite integer inside zero through two hundred fifty-five; values such as one hundred twenty-eight point five fail validation rather than being rounded, and negative or two-hundred-fifty-six-plus values fail with a message that names the channel and states that it must stay inside zero through two hundred fifty-five.

Warm orange-heavy triples typically produce lower kelvin values near domestic tungsten ranges; cooler blue-heavy triples produce higher kelvin near daylight ranges. Remember that McCamy is an approximation optimized for a practical chromaticity neighborhood; extreme out-of-locus colors can yield extreme or less meaningful temperatures even when arithmetic succeeds, so treat the number as a deterministic estimate rather than a laboratory measurement.

Where RGB-to-Kelvin conversion fits in design, lighting, and software

Lighting designers meet this mapping when a mock-up uses screen RGB swatches and a production brief expects approximate kelvin tags for warm, neutral, or cool scenes, when two UI states should be labeled with relative warmth, or when a lookbook documents both hex and a rough CCT note side by side.

Photographers and video engineers use it when a reference color from a chart or frame grab needs a quick CCT estimate for whiteboard notes, when comparing graded looks that claim daylight versus tungsten balance, or when teaching white-balance concepts without specialized meters. Students see it in computer-graphics and color-science courses that introduce chromaticity after sRGB and XYZ, in digital photography classes that move between RGB pickers and kelvin sliders, and in interview warm-ups that ask for a mental convert of a short triple into a temperature band.

Pair it with Kelvin-to-RGB tools when you need the reverse direction, and with other free deterministic converters when you are building a small lab for design-system hygiene.