Color Temperature Mired Calculator (K ↔ Mired + CTO / CTB gel picker)
Kelvin is not a perceptually linear unit — the visible jump from 6500 K to 5500 K is not the same as from 5500 K to 4500 K. Film and photo crews therefore work in *Mireds* (M = 10⁶ ÷ K), where equal mired steps look like equal white-point shifts to the eye. This tool converts both directions and, given a source and target, recommends the closest standard Rosco / Lee CTO (warming) or CTB (cooling) gel strength.
Common temperatures
Enter a colour temperature between 1000 and 20 000 K
Source is too cool — add a **CTO** (orange) gel to warm the light toward the target.
Notes
- Mired = 10⁶ ÷ Kelvin. Mireds are the *perceptually linear* unit for colour temperature — the human eye registers white-point drift roughly as 1/K, so equal-mired steps look like equal visible shifts. That makes Mireds, not Kelvins, the natural working unit on a film / video set.
- Sign convention: shift = target Mired − source Mired. **Positive** (target K is lower) → warm the light with a *CTO* (Color Temperature Orange) gel. **Negative** (target K is higher) → cool it with a *CTB* (Color Temperature Blue) gel. Around 10 mired equals the weakest 1/8 gel; any smaller is usually invisible.
- Filter values follow the Rosco / Lee standards: Full CTO +159, 1/2 +81, 1/4 +42, 1/8 +21; Full CTB −137, 1/2 −68, 1/4 −35, 1/8 −18. Lee 201 (Full CTB) is rated −131 — about 5 mired off; measure on set when colour accuracy matters.
Formula
M = 10⁶ ÷ K K = 10⁶ ÷ M ΔMired = M_target − M_source // positive → warm (CTO); negative → cool (CTB) residual = ΔMired − chosen gel Mired // sanity-checks the strength you picked
- · Common sources (CIE / Kodak): candle ≈ 1900 K (526 M), tungsten 3200 K (313 M), halogen 3400 K (294 M), white fluorescent 4000 K (250 M), daylight 5500 K (182 M), cloudy 6500 K (154 M), blue-sky shade 8000–10 000 K.
- · Mireds are *perceptually linear*: the eye sees white-point drift roughly as 1/K, so equal mired steps look like equal visible shifts — equal Kelvin steps actually look bigger near tungsten and smaller near daylight.
- · Rosco-standard mired shifts (industry baseline): Full CTO +159, 1/2 +81, 1/4 +42, 1/8 +21; Full CTB −137, 1/2 −68, 1/4 −35, 1/8 −18. Lee 201 (Full CTB) is rated −131 — about 5 mired off; measure on set when accuracy matters.
- · Sign convention: the source is the reference. A positive shift means we need to warm the source (use CTO to drag a high-K source down). A negative shift means we need to cool it (use CTB to drag a low-K source up).
- · Visible threshold: a shift of less than ~10 mired is usually below the eye-noticeable level — weaker than even the lightest 1/8 gel. The tool returns "no gel needed" in that band.
- · Mixed-light sets: when window daylight (5500 K) hits a tungsten interior (3200 K), the mired delta is the gel you need to balance them — gel one source to align the white points so the frame isn't cool on one side and warm on the other.
- · Sources: Rosco "Filter Facts" technical guide (Cinegel mired shifts); Lee Filters "Lighting Filters" catalogue.
Frequently asked
Why convert to Mired instead of just working in Kelvin?
Because Kelvin is not perceptually linear. The visible white-point shift from 6500 K to 5500 K is much smaller than the shift from 3500 K to 2500 K, even though both are 1000 K apart. The eye perceives white-point drift roughly as a linear function of *1/T* (chromaticity 1/T), and *Mired = 10⁶ ÷ K* is exactly a scaled 1/T. So *adding the same Mired amount* produces the same visible warming regardless of the starting temperature. A +50 mired gel applied to a 5500 K source (→ 232 M → 4310 K, a 1190 K change) and the same gel applied to a 3200 K source (→ 362 M → 2762 K, a 438 K change) cover wildly different Kelvin distances but look the *same amount warmer*. That is why filter manufacturers (Rosco, Lee) label their gels by mired shift rather than Kelvin.
What is the difference between CTO, CTB, CTS, and Plusgreen?
CTO (Color Temperature Orange) is a warming gel: it adds positive mireds, taking a *daylight / HMI / 5500 K LED* down to tungsten 3200 K, used for evenings and mixed-light interiors. CTB (Color Temperature Blue) is a cooling gel: it adds negative mireds, taking *tungsten 3200 K* up to daylight 5500 K, used for daylight scenes or windows. CTS (Color Temperature Straw) is a softer, yellowish alternative to CTO — its chroma is slightly different (a touch greener), which often looks more natural on skin under digital sensors, and it has become a common substitute in modern shoots. Plusgreen (also called "plus green" or "minus green") *corrects hue, not colour temperature* — fluorescents and cheap LEDs often skew green or magenta (poor CRI), so Plusgreen adds green to match fluorescents and Minusgreen (magenta) removes the green cast. Easy rule: CTO / CTB / CTS move along the *blue–yellow axis* (colour temperature); plus/minus green moves along the *green–magenta axis* (hue) — they are independent.
My camera white balance already adjusts Kelvin — do I still need physical gels?
Physical gels are still essential whenever a *single frame contains multiple light sources at different temperatures*. The camera's white balance is one global value: setting it to 5500 K assumes the whole frame is 5500 K, but if your key is 5500 K window light and your fill is 3200 K tungsten, picking either WB makes the other source look wrong (the tungsten goes orange, or the window goes blue). Gelling *just one source* on set drags the two sources into the same neighbourhood so the RAW already shows roughly matched white points, and post can finish the colour cleanly. For single-source scenes, white balance alone is fine — but for mixed indoor / outdoor light, stage shows and event work, gels are still everyday tools. Quality gels (e.g. Rosco) also filter the spectrum more cleanly than digital WB compensation, which can introduce noise or banding when you push WB far in post, especially when skin tones matter.
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Convert between m/s, ft/min, km/h, knots and ft/s — the five vertical-speed units used in aviation instruments, mountaineering and dive ascent-rate guidance.
Butter Unit Converter (Sticks / Grams / Tablespoons / Cups)
Baking butter conversions: enter any one quantity (sticks, grams, tablespoons or cups) and the tool returns the equivalent in the other three units.
Candy / Sugar Stage Temperature Reference Calculator
Enter syrup temperature (°C or °F) to instantly see the candy stage (thread / soft ball / firm ball / hard ball / soft crack / hard crack / light caramel / dark caramel), its full range and typical dessert use.
LED Display Pixel Pitch & Optimal Viewing Distance Calculator
Enter the LED panel pixel pitch (P-value, e.g. P2.5 / P4) plus screen width × height — get the effective resolution, pixel density and the minimum / comfortable / visual-fusion viewing distances so you size the right panel for any AV install.
Pixels Per Degree (PPD) VR / Display Calculator
Enter the horizontal / vertical pixel count and the corresponding field of view (FOV) — get the pixels-per-degree (PPD), the industry-standard metric for comparing VR headsets, monitors and TVs against the retinal-resolution benchmark (~60 PPD).
CSS Aspect Ratio Padding Calculator
Enter an aspect ratio (e.g. 16:9 or 16/9) — instantly get the padding-bottom percentage and matching CSS snippet (plus the modern aspect-ratio property), for responsive video / iframe containers.
RGB ↔ CMYK Color Converter
Enter RGB (0–255) and instantly get the CMYK percentage values (K, C, M, Y), with matching hex code and printing-friendly tips on the screen-sRGB → CMYK gamut gap.