What about UV 12 or higher?

WHO’s scale has no upper bound — the top category is written “11+”. The arithmetic continues unchanged: at 12 every threshold on this page is multiplied by 11/12, at 13 by 11/13, and so on.

WHO category: Extreme (11+)

How long does it take to burn in UV 11?

At UV index 11, the erythemal-dose model computes a first-perceptible-reddening reference dose after roughly 12 minutes of continuous unprotected exposure for Fitzpatrick skin type I, and roughly 61 minutes for type VI. The full type I–VI table is below, with the arithmetic and the sources.

Computed from a dose rate of 9.9 standard erythema doses per hour at UV index 11. Reference values, not measurements of any individual.
Fitzpatrick skin type	Reference dose to first erythema (SED)	Minutes to that dose at UV 11	0.6 × that figure (min)
Type Ialways burns, never tans	2	12	7
Type IIusually burns, tans minimally	2.5	15	9
Type IIIsometimes mild burn, tans uniformly	3.5	21	13
Type IVburns minimally, always tans well	4.5	27	16
Type Vvery rarely burns, tans easily	6	36	22
Type VIdeeply pigmented, never burns	10	61	36

The fourth column is a fixed 0.6 multiple of the third — an arithmetic margin for the roughly ±30–50% spread in published reference doses within one phototype. It is what the app reports.

“Reporting burn times is not recommended.”

— WHO, WMO, UNEP and ICNIRP, Global Solar UV Index: A Practical Guide, WHO/SDE/OEH/02.2 (2002)

The guide gives its reasoning directly: “people tend to interpret burn times to mean that there is a safe level of unprotected sun exposure”, and relating index values to a time to burn therefore “sends out the wrong message”.

Why we publish the figure anyway →

This page answers the UV 11 question. The app answers yours.

Real days do not sit at 11 — the index climbs to a peak and falls again. Safe Sun Window takes your skin type and the index where you actually are, and runs this same calculation on those inputs. Free, no account, no ads. Return visits are counted with a random first-party id that goes to no one else. If you turn on location, your device rounds your position to about 10 km before it reaches our weather provider for the UV reading, with no id attached.

Open Safe Sun Window →

What UV 11 means

Eleven opens WHO’s Extreme band, and that band is open-ended: Table 1 ends at “11+”, with no upper bound in the published scale. Readings above 11 are not exotic — the WHO guide’s own worked example of daily reporting shows a clear-sky maximum of 13 for Darwin, Australia, on 27 March 2002.

Because the band has no ceiling, this page is also the page for 12, 13 and above: the modelled thresholds simply keep shortening in proportion. At 12 they are 11/12 of the values below; at 13, 11/13.

Where and when UV 11 actually occurs

Eleven and above need the sun close to directly overhead, and usually a second factor on top. Readings of 11 or more typically come from:

Tropical latitudes when the sun passes close to overhead at solar noon — WHO’s own example records a clear-sky maximum of 13 at Darwin (12°S).
High-altitude tropical and subtropical sites, where the 10–12%-per-1000-metres altitude effect compounds a base reading that is already at the top of the scale.
Midday in the sunniest parts of the southern subtropics in high summer.
Locations combining a high sun with strongly reflective ground — which raises received dose without raising the reported index, since the index is defined for a horizontal surface.

At 11 and above the whole daylight curve is shifted up, not just its peak. A place peaking at 12 or 13 is typically still in WHO’s High or Very high bands for several hours either side of solar noon, so the elevated portion of the day is measured in hours.

The six factors WHO lists as setting the index, with its own figures →

What the published guidance says at UV 11

The US EPA publishes for 8 and above — which includes the whole Extreme band: “Extra protection needed. Be careful outside, especially during late morning through mid-afternoon. If your shadow is shorter than you, seek shade and wear protective clothing, a wide-brimmed hat, and sunglasses, and generously apply a minimum of SPF-15, broad-spectrum sunscreen on exposed skin.”

WHO assigns the Extreme band the colour code Purple (PMS 265) in its international scheme, and its underlying protection recommendation is unchanged from UV 3: the same set of measures, applied to a day that delivers erythemal dose almost four times faster.

The published scheme is binary, not graded: the same measures apply from UV 3 upward, and what changes with the index is the rate at which erythemal dose accumulates. Why the scheme is not graded →

Check the arithmetic

At UV 11, an hour of continuous exposure delivers 11 × 0.9 = 9.9 standard erythema doses. Fitzpatrick type II’s reference dose is 2.5 SED, so 2.5 ÷ 9.9 × 60 = 15 minutes. Every row in the table above is that division with a different reference dose.

The 0.9 factor is exact, and follows from the definition of the index; the reference doses are not. Where the 0.9 comes from, and what the reference doses are →

Questions

How long does it take to burn in UV 11?: At UV index 11 the model computes a first-erythema reference dose in about 12 minutes of continuous unprotected exposure for Fitzpatrick type I skin and about 61 minutes for type VI. These are computed model outputs for a reference dose, not durations of demonstrated safety.
What about UV 12 or higher?: WHO’s scale has no upper bound — the top category is written “11+”. The arithmetic continues unchanged: at 12 every threshold on this page is multiplied by 11/12, at 13 by 11/13, and so on.

Other UV levels

All levels, the full method, and why burn times are contested →

Sources for the figures above

World Health Organization, World Meteorological Organization, United Nations Environment Programme and International Commission on Non-Ionizing Radiation Protection. “Global Solar UV Index: A Practical Guide.” WHO/SDE/OEH/02.2, 2002.
ISO 17166:1999 / CIE S 007/E-1998. Erythema reference action spectrum and standard erythema dose.
United States Environmental Protection Agency. “UV Index Scale.” epa.gov, last updated 15 June 2026; verified 3 August 2026.
Fitzpatrick TB. “The validity and practicality of sun-reactive skin types I through VI.” Archives of Dermatology, 1988;124(6):869–871.
Minimal-erythema-dose values per Fitzpatrick phototype — working reference values, range-checked against ISO 17166:1999; the six-value progression itself is not traced to a named primary document.

Full annotated source list, with what each one is used for →