Vitamin D3 Conversion: Micrograms to International Units
0.25 micrograms (mcg) of vitamin D3 equals 10 International Units (IU).
Standard Conversion Formula
The universally accepted conversion for vitamin D3 (cholecalciferol) is straightforward 1:
- 40 IU = 1 mcg 1
- Therefore: 0.25 mcg × 40 = 10 IU
This conversion factor is consistent across all clinical guidelines and applies to both vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) when measuring potency 1.
Clinical Context
To put this dose in perspective:
- Standard infant supplementation is 400 IU/day (10 mcg/day), which equals 40 times this amount 2
- Standard adult maintenance ranges from 600-800 IU/day (15-20 mcg/day), which equals 60-80 times this amount 1
- Therapeutic loading doses for deficiency are typically 50,000 IU weekly (1,250 mcg weekly), which equals 5,000 times this amount 1, 3
A dose of 0.25 mcg (10 IU) represents a negligible amount of vitamin D3 and would have no meaningful clinical effect on vitamin D status 1, 3.
Important Conversion Notes
- This conversion applies specifically to cholecalciferol (vitamin D3), which is the preferred form for supplementation due to its superior potency and longer duration of action compared to ergocalciferol (vitamin D2) 4, 5
- When reading supplement labels or prescriptions, always verify whether the dose is expressed in micrograms (mcg) or International Units (IU), as confusion between these units can lead to significant dosing errors 1
- The conversion remains constant regardless of the route of administration (oral, intramuscular, or intravenous) 1, 3