Skip to content
This page is also available in your language. Switch

Sync settings

Choose what your account keeps in step on every device where you are signed in.

  • My tools

    Always synced: the tools on your board, their order and size.

  • The windows open on your start page, including what you typed in them.

  • Every note in the notepad – on the notepad page, on your board and in windows.

  • Every list of website shortcuts – on the shortcuts page, on your board and in windows.

  • Every grid in the cover grid maker – on its page, on your board and in windows.

  • Every list of bookmarked organisations in the OIN lookup – on its page, on your board and in windows.

  • Keeps your pipeline and saved recipes on all your devices. Your files are never synced – only the steps and settings.

Turning something off removes it from your account straight away. Your devices keep their own copy.

Notifications

Tools that can tell you about something new while a Synsi tab is open, even when you are in another tab or app. Choose them for this browser.

This browser cannot show notifications from websites.
Notifications are blocked for this site. Allow them in your browser’s site settings (the icon left of the address), then switch them on here.

  • Says “New message” while a Synsi tab is open – never who wrote it or what.

Your choice is stored in this browser only. Notifications never show personal content such as a message or a number. They work while a Synsi tab is open; closed tabs get none.

Browse all tools →

Vitamin D Calculator – IU, µg and the Daily Upper Limit

Use the vitamin D calculator to convert your dose between IU and µg and compare your total daily intake with the reference intake and upper limit.

My tools →
Unit
µg
Sex

For information only, not medical advice. Reference values describe healthy population groups and do not tell you what dose you should take. Ask a doctor, pharmacist or dietitian before starting, stopping or combining supplements, especially if you are pregnant, take medication or have a health condition.

Reference values are for adults aged 19 and over. Children have different, lower limits. Sources: US Dietary Reference Intakes (NIH Office of Dietary Supplements) and EFSA Dietary Reference Values and Tolerable Upper Intake Levels (2024). Reviewed October 7, 2026.

Runs in your browser – your data never leaves your device Also available via our free API

How to use the Vitamin D Calculator

  1. 1 Enter the vitamin D amount per serving and choose IU or µg as on the label.
  2. 2 Set servings per day and, if you know it, the vitamin D you get from food and other supplements.
  3. 3 Compare the daily total with the reference intake and the upper limit for your age.

IU and micrograms

Vitamin D is labelled in international units (IU) or micrograms (µg, also written mcg). The conversion is fixed: 1 µg = 40 IU, so 10 µg is 400 IU, 25 µg is 1,000 IU and 100 µg is 4,000 IU. The same factor applies to vitamin D3 (cholecalciferol) and D2 (ergocalciferol).

Reference intake and upper limit

  • The US RDA is 15 µg (600 IU) per day for adults up to 70 and 20 µg (800 IU) from age 71, including pregnancy and breastfeeding.
  • EFSA set an Adequate Intake of 15 µg per day for adults, assuming little vitamin D is made in the skin.
  • Both authorities set the upper limit at 100 µg (4,000 IU) per day for adults, including pregnant and breastfeeding women. The limit includes vitamin D from food and all supplements.

A daily dose of 4,000 IU therefore reaches the upper limit on its own, before food or a multivitamin is counted. Doctors sometimes prescribe higher doses for a limited period to treat a deficiency; the upper limit is not meant for supervised treatment.

Your vitamin D status is measured in the blood

How much vitamin D you need from supplements depends on sun exposure, skin type, body weight, diet and health. The calculator cannot tell whether you are deficient. Clinicians assess vitamin D status with a blood test for 25-hydroxyvitamin D (25(OH)D). Many guidelines consider levels below 25–30 nmol/L (10–12 ng/mL) deficient and above about 50 nmol/L (20 ng/mL) adequate for most people, although cut-offs vary.

Sun, season and diet

In summer, skin exposed to sunlight produces vitamin D. At northern latitudes, such as the Netherlands, the UK and Canada, the sun is too low between roughly October and March for meaningful production. Food sources include oily fish, egg yolks and fortified foods like some margarines and plant drinks, but it is difficult to reach the reference intake from food alone.

Common doses compared

A typical supplement of 10 µg (400 IU) provides two thirds of the US RDA; 25 µg (1,000 IU) provides 25% of the upper limit; 50 µg (2,000 IU) provides half of it.

Sources

Frequently asked questions

How many µg is 1,000 IU of vitamin D?

1,000 IU is 25 µg. Divide IU by 40 to get micrograms.

Is 4,000 IU of vitamin D a day too much?

4,000 IU (100 µg) is exactly the adult upper limit in both the US and EU, before counting food or other supplements. Do not exceed it long-term without medical advice.

Does vitamin D2 or D3 make a difference to the calculation?

No. 1 µg is 40 IU for both forms. D3 is the form most supplements contain.

How do I know if I need vitamin D?

Only a blood test for 25-hydroxyvitamin D shows your status. Ask your doctor, especially if you get little sun, have dark skin, are over 70 or are pregnant.

Last updated: