Vitamin D mcg to IU: a dose chart with what each dose means

Multiply micrograms by 40 and you have IU. Divide IU by 40 and you’re back to micrograms. The factor is the same for D3 (cholecalciferol) and D2 (ergocalciferol), and NIH ODS, EFSA and the FDA all use it. If you’d rather not do sums, type in the number from your bottle:

Vitamins A and E convert differently. For those, use the general IU to mcg and mg converter.

Vitamin D mcg to IU chart: 2.5 to 250 mcg

The right-hand column says what each figure means in official advice. Where a dose has no advice of its own, you’ll see the nearest reference point.

A recommended amount is what most people need. An upper limit is how much you can take every day, long term, without harm. There’s a wide gap between the two, and 10 mcg and 25 mcg bottles sit comfortably inside it.

10, 15, 25, 50 and 125 mcg of vitamin D in IU

• 10 mcg = 400 IU. The daily amount the NHS advises for nearly everyone from October to March.
• 12.5 mcg = 500 IU.
• 15 mcg = 600 IU, the US figure for adults up to 70.
• 25 mcg = 1,000 IU, a common strength for softgels and drops.
• 50 mcg = 2,000 IU. Half the adult limit, and the whole limit for a child under 11.
• 125 mcg = 5,000 IU. A popular bottle on iHerb, but above the 100 mcg limit.

1,000, 2,000, 4,000, 5,000 and 10,000 IU in mcg

To go the other way, divide by 40:

• 1,000 IU is 25 mcg;
• 2,000 IU is 50 mcg;
• 4,000 IU is 100 mcg, exactly the adult limit;
• 5,000 IU is 125 mcg;
• 10,000 IU is 250 mcg. NIH ODS says signs of toxicity are unlikely below this, yet it’s still two and a half times the limit;
• 50,000 IU is 1,250 mcg, or 1.25 mg. If a doctor prescribes a capsule like this, they also tell you how often to take it.

Why vitamin D is hardly ever given in mg

Vitamin D doses are tiny. 125 mcg is 0.125 mg and 10 mcg is 0.01 mg. In milligrams you end up with strings of zeros after the decimal point, which is where mistakes creep in. That’s why the FDA requires vitamin D on labels in mcg and allows IU in brackets as an extra. The NHS and EFSA give their figures in micrograms too, and UK labels show % NRV rather than % DV.

The mistake to avoid is mixing up mg and mcg. 1 mg = 1,000 mcg. A note saying “0.5 mg” means 500 mcg, or 20,000 IU, five times the adult limit. If you see a dose in mg, multiply by 1,000 first and only then by 40.

Why vitamin E has a different factor, and where IU came from, is explained in what an IU on a vitamin label means. With vitamin E the form matters as well: see vitamin E IU to mg.

Which vitamin D dose suits you

The NHS says 10 mcg, US tables say 15–20 mcg, and the bottle a friend recommended says 1,000 IU. They don’t contradict each other: they’re maintenance amounts with different margins, and all of them sit below the limit. Pick your situation:

Forms, D3 with K2 and timing are covered in how much vitamin D3 to take. If you’ve had a blood test, our page on vitamin D test results explains the numbers.

Upper limits for children and adults

EFSA reviewed the limit in 2023 and kept 100 mcg for adults, including during pregnancy and breastfeeding. The NHS and US figures are the same, and from age 11 the adult limit applies.

Children’s limits are two to four times lower than the adult one. Don’t split a 50 mcg adult softgel by eye for a toddler: children’s doses come from your health visitor or GP, and our page on vitamins for children covers the rest.

When to talk to your GP or pharmacist first

NIH ODS notes that vitamin D overdose almost always comes from supplements, not from food or sunshine. Check with your GP or pharmacist if:

• you take orlistat, a statin, steroids or a thiazide diuretic, all of which NIH ODS lists as interacting with vitamin D;
• you have kidney disease or have had high calcium in a blood test;
• you’re already on a treatment course, in which case don’t add your own bottle on top;
• you’re pregnant and want more than 15 mcg (600 IU) a day;
• the vitamin D is for a child.

How to choose vitamin D3 on iHerb by dose

1. Find the Vitamin D3 line in the Supplement Facts panel and read the mcg figure. The IU in brackets is for cross-checking.
2. Check the serving: one softgel or two, and how many drops.
3. Add up the D3 from every bottle: multivitamin, calcium with D3, cod liver oil.
4. Compare the total with the limits table. For an adult, that’s no more than 100 mcg a day.
5. For the other lines on the panel, see how to read a supplement label.