How bright can your colour actually get?
Every colour has a luminance it cannot pass while staying exactly itself. Enter a hex value and see that ceiling, plus what each glow mode would deliver.
This is a free online HDR colour limit calculator. Enter any hex colour and it computes the highest absolute luminance, in nits, that colour can reach while remaining exactly itself in Rec.2020. The limit varies enormously by hue because luminance is not shared evenly between primaries: white reaches 10,000 nits, green 6,780, red 2,627, and fully saturated blue only 593. Past that ceiling a colour must either shift hue or lose saturation to get brighter. Knowing the number in advance explains why a saturated brand blue glows less than a white wordmark. Free, no account.
Selected colour
Royal blue#176BFF
Exact-colour ceiling
1,972nits
The brightest this colour can be while staying exactly itself.
Asking for 4,000 nits
Computed live by the same solver the editor uses. These are encoding-gamut limits from the BT.2020 matrix and PQ’s component ceiling — a physical display will usually reach less.
Why saturated colours have different limits
Making a colour brighter without changing it means scaling its three linear components by the same factor. The ceiling arrives when the largest of them reaches the top of the PQ range — and because luminance is a lopsided weighted sum of the three, colours run out at wildly different points.
What happens past the ceiling
Something has to give: brightness, saturation, or hue. Clipping a channel gives up hue and does it uncontrollably, which is why a naively brightened orange drifts toward yellow. The solver instead blends toward the neutral of the same luminance, so brightness stays fixed while chroma falls — turning one uncontrolled outcome into two separate dials.
Questions
Where does the ceiling number come from?
Convert the colour to linear Rec.2020, then find the largest scale factor that keeps every channel inside PQ’s component range — 10,000 nits, which is 49.26 times the 203-nit reference white. Scaling all three channels equally is what preserves chromaticity, so the first channel to reach the ceiling sets the limit.
Why is white 10,000 and blue only 806?
Under the BT.2020 coefficients, luminance is 0.2627·R + 0.6780·G + 0.0593·B. Blue contributes under 6%, so a saturated blue drives its blue channel to the ceiling while the light output is still low. White spreads the load across all three channels and reaches the top of the range.
Does this mean my display can produce that many nits?
No. These are limits of the encoding, not of any panel. A very good consumer HDR display peaks around 1,600 nits, and only over a small area. The calculator tells you what the file can legally ask for.
What is ΔE ITP?
A colour difference measured in ICtCp, the perceptual space defined for HDR. Roughly 1.0 is one just-noticeable difference. It is used here instead of an SDR metric because those stop being meaningful well above diffuse white.
Why does Preserve sometimes deliver the full 4,000?
Because that colour’s ceiling is already above 4,000. Yellow, cyan, green and white all clear it comfortably, so there is nothing to cap and no saturation to spend.
What are the numbers?
Every figure below is either a published constant or a value this tool computes. None is an estimate, and each one is traceable to the standard beside it.
| Measurement | Value | Source |
|---|---|---|
| Diffuse white reference | 203 nits | ITU-R BT.2408 |
| PQ maximum | 10,000 nits | SMPTE ST 2084 |
| 8-bit PQ code for diffuse white | 148 | Computed |
| 8-bit PQ code for 1,600 nits | 205 | Computed |
| Rec.2020 white ceiling | 10,000 nits | Computed |
| Rec.2020 green ceiling | 6,780 nits | Computed |
| Rec.2020 red ceiling | 2,627 nits | Computed |
| Rec.2020 blue ceiling | 593 nits | Computed |
| Blue's share of Rec.2020 luminance | about 6% | Computed |
| LinkedIn logo size | 400 × 400 px | Measured |
| LinkedIn post and ad size | 1200 × 627 px | Measured |
| LinkedIn JPEG re-encode | quality 90, 4:4:4 | Measured |
| Price | Free, no account | This site |
Where do these figures come from?
This tool implements published standards rather than an in-house approximation of them. Each specification below defines part of what the exported files contain.
- ITU-R BT.2100
Defines the HDR system this tool encodes into — BT.2020 primaries with the PQ transfer function.
- ITU-R BT.2408
Sets diffuse white at 203 nits, which is the reference every brightness figure here is measured against.
- SMPTE ST 2084
The PQ transfer function itself: absolute luminance from 0 to 10,000 cd/m², independent of display.
- ITU-T H.273
The code points behind cICP 9 16 0 1 — colour primaries, transfer characteristics, matrix and range.
- W3C PNG Third Edition
Specifies the PNG cICP chunk, which is how an HDR PNG declares itself without an ICC profile.