sunscreen.fans

How long until
you burn?

A forecast-aware estimate for right now—plus an honest look at what SPF can and can’t promise.

1 How does your skin react to sun?

Choose by how you burn and tan—not colour alone.

2 Where are you?
or
Enter a UV Index manually
Choose a location to see your estimate.

Good protection starts
with good information.

01

SPF decoded

It measures dose,
not hours.

SPF 30 means properly protected skin needed 30 times the sunburn-causing UV dose to burn in a laboratory test than unprotected skin. It mainly describes UVB sunburn protection. It does not guarantee 30 times longer outside because UV intensity, application, water, sweat, and wear all change real protection.

SPF
30
02

Broad spectrum

UVA and UVB
both matter.

UVB is the main cause of sunburn. UVA penetrates more deeply and contributes to skin ageing and cancer. “Broad spectrum” means protection across both.

03

How filters work

They reduce UV
reaching your skin.

Both mineral and organic filters mostly absorb UV energy and release it as tiny amounts of heat. Some mineral filters also scatter a small portion. Neither type forms an invincible shield.

Your five-point
sun plan.

  1. 1

    Choose broad spectrumUse SPF 30 or higher for extended outdoor time.

  2. 2

    Use enoughMost adults need about a shot glass for exposed face and body.

  3. 3

    Apply before exposureFollow the label; many products say 15 minutes before going out.

  4. 4

    Reapply generouslyUse our conservative 90-minute reminder, and sooner after water, sweat, or towelling.

  5. 5

    Add shade and clothingA hat, sunglasses, sleeves, and shade do work sunscreen cannot do alone.

How we calculate
your estimate.

UV Index is converted to erythemally weighted energy and accumulated against a representative minimal erythema dose for your selected skin type. The forecast is sampled every five minutes until sunset.

Core relationship

UV irradiance = UVI × 0.025 W/m²

Skin response varies widely—even within one Fitzpatrick type. Medication, altitude, reflective water or snow, previous exposure, clouds, and application quality can all move the real result.

Sources & further reading