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Vitamin D IU to mcg converter

Convert an existing vitamin D2 or D3 food or supplement label amount between IU and micrograms without choosing a dose or interpreting a blood result.

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Calculate your result

Enter the vitamin D2 or D3 amount from one unchanged label basis, such as per serving, per drop or per day. Do not use thousands separators; use a full stop or an unambiguous comma for decimals.

Accepted range: 0 to 10000000 IU vitamin D

Your result will appear here

Nothing is saved or added to the URL.

What this result means

Choose the direction and enter the vitamin D amount from the label. For vitamin D2 and D3, 1 microgram (mcg or µg) equals 40 international units (IU), so IU ÷ 40 gives mcg and mcg × 40 gives IU. [1][2][3]

Vitamin D IU are substance-specific

An international unit describes biological activity, so its mass relationship is not universal. The 40 IU per microgram relationship here is specifically for vitamin D2 and D3. Do not reuse it for vitamin A, vitamin E, insulin, medicines or another substance. [1][3]

Keep the label basis unchanged

If the original amount is per serving, the converted amount is also per serving. If it is per drop or per day, that basis remains unchanged. The converter changes only IU and mcg; it does not multiply servings, drops or days. [1][3]

Supplement units are not blood-test units

Vitamin D food and supplement labels use IU or mcg. A 25-hydroxyvitamin D blood result is commonly reported in ng/mL or nmol/L and represents a measured concentration, not the amount on a supplement label. This converter cannot translate an oral amount into a blood result. [4]

How the result is rounded

The calculator uses 0.025 mcg per IU or the exact inverse of 40 IU per mcg and rounds once at the end. Mcg is shown to three decimal places and IU to two decimal places. A positive value smaller than the display resolution appears as less than 0.001 mcg or less than 0.01 IU instead of zero. Extra displayed digits do not make a rounded source label more precise. [1][3]

Safe next steps

Keep the original label beside the converted value and check whether the amount applies to one serving, one drop or a full day. If you need to decide how much vitamin D to take, use advice that accounts for your age, health, medicines, diet and local guidance rather than treating a unit conversion as a recommendation. [2][4]

Formula and assumptions

Formula
Vitamin D (mcg) = vitamin D (IU) × 0.025, which is IU ÷ 40. Vitamin D (IU) = vitamin D (mcg) × 40. [1][2][3]
Version
Vitamin D2 and D3 label-unit conversion, vitamin-d-d2-d3-label-unit-conversion-v1
Rounding
Calculate with the exact inverse factors, then round once for display: mcg to three decimal places and IU to two decimal places. Positive values below display resolution use a less-than result; source-label rounding is not corrected.
Worked example
A vitamin D label showing 1,000 IU per serving is 1,000 ÷ 40 = 25.000 mcg per serving. Converting 25 mcg back gives 25 × 40 = 1,000.00 IU. [1][2]

Who this is for — and when not to use it

Intended use

Neutral conversion of an existing vitamin D2 or D3 amount between IU and micrograms on the same food or supplement label basis.

Not intended for

This tool does not choose, check or change a dose; classify an amount as safe, high, low or recommended; interpret or predict a vitamin D blood result; convert active vitamin D medicines; or convert any other substance's IU.

Exclusions

  • 25(OH)D blood-test values in ng/mL or nmol/L
  • Dose selection, safety checking, upper-limit comparison or treatment advice
  • Prediction of blood vitamin D response from an oral amount
  • Calcitriol, calcifediol, alfacalcidol and other active vitamin D medicines or analogues
  • IU conversion for vitamin A, vitamin E, insulin, medicines or any other substance
  • Milligrams, drops, liquid concentration, serving count or bottle-duration arithmetic
  • Pregnancy, paediatric, kidney, parathyroid or other condition-specific decisions

Evidence sources

  1. 1. Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels — United States Food and Drug Administration. Accessed Aug 10, 2026.
  2. 2. Vitamins and minerals: Vitamin D — National Health Service. Accessed Aug 10, 2026.
  3. 3. Elements within the Nutrition Facts table — Canadian Food Inspection Agency. Accessed Aug 10, 2026.
  4. 4. Vitamin D Fact Sheet for Consumers — United States National Institutes of Health. Accessed Aug 10, 2026.