Vitamin D Sun Calculator
Vitamin D Exposure Calculator
Optimize your sun intake safely.
Disclaimer: This tool provides estimates only. Factors like age, altitude, and cloud cover affect synthesis. Always avoid painful sunburns and consult a healthcare professional.
Fitzpatrick Skin Scale
Melanin acts as a natural biological filter for UV radiation. Consequently, individuals with darker skin require longer exposure to produce the same amount of Vitamin D as those with lighter skin.
| Skin Type | Description | Sun Sensitivity |
| Type I | Very fair, red/blonde hair | Always burns, never tans |
| Type III | Creamy white, fair | Sometimes burns, tans gradually |
| Type VI | Deeply pigmented (dark brown/black) | Never burns, deeply pigmented |
Role of the UV Index
It’s specifically produced by UVB rays. Unlike UVA rays (which are present all day), UVB rays are strongest when the sun is at its zenith (highest point).
Low UV (1–2): Minimal production; usually occurs in early morning, late evening, or winter.
Moderate to High UV (3–7): Ideal window for synthesis (often between 10:00 AM and 3:00 PM).
Very High UV (8+): Rapid synthesis, but significantly higher risk of DNA damage and sunburn.
Surface Area and “The Shadow Rule”
The more skin you expose, the less time you need. Exposing your back or legs is far more efficient than just exposing your face and hands. A simple way to check if you are producing it is the Shadow Rule:
If your shadow is shorter than you, your body is actively producing it. If your shadow is longer than you, the atmosphere is filtering out most UVB rays.
Health & Safety Guidelines
Winter: In regions above $37^\circ$ latitude (e.g., San Francisco, Richmond, or Athens), UVB rays are too weak to produce it from roughly November to March, regardless of cloud cover.
Avoid Sunburn: Synthesis stops once the skin reaches its “pink” threshold. Staying out longer does not increase Vitamin D; it only increases skin damage.
Glass Blocking: Standard window glass blocks nearly 100% of UVB rays. You cannot get it through a closed window at home or in a car.
