How to Calculate Vitamin D
What is Vitamin D?
Vitamin D is synthesised in skin on exposure to UVB radiation (sunlight wavelength 280–315 nm). In the UK, sufficient UVB is only available from April to September (10am–3pm). During winter months (October–March), the sun is too low in the sky to provide adequate UVB at UK latitudes, so supplementation is recommended for most people.
Step-by-Step Guide
- 1Melanin in skin absorbs UVB — darker skin requires more sun exposure
- 2Fair skin: 10–15 min/day (summer) provides adequate vitamin D
- 3Dark skin: 40–60 min/day (summer) required
- 4NHS recommends 10 mcg (400 IU)/day supplement for everyone October–March
- 5Vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol)
Worked Examples
Frequently Asked Questions
What is Vitamin D?
Vitamin D is synthesised in skin on exposure to UVB radiation (sunlight wavelength 280–315 nm). In the UK, sufficient UVB is only available from April to September (10am–3pm)
How accurate is the Vitamin D calculator?
The calculator uses the standard published formula for vitamin d. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.
What units does the Vitamin D calculator use?
This calculator works with inches. You can enter values in the units shown — the calculator handles all conversions internally.
What formula does the Vitamin D calculator use?
The calculator applies the standard formula for this type of calculation. See the 'How It Works' steps above for the detailed formula breakdown.
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