How do I convert mg to International Units (IU)?

The conversion from mg to IU is substance-specific — there is no single universal factor. Common examples: Vitamin D: 1 IU = 0.025 mcg (so 1,000 IU = 25 mcg = 0.025 mg). Vitamin E (natural): 1 IU = 0.67 mg. Vitamin A (retinol): 1 IU = 0.3 mcg = 0.0003 mg. Always refer to the specific substance's IU definition.

What does 'per kg body weight' mean in drug dosing?

Many medications are dosed based on the patient's body weight to account for differences in distribution and metabolism. For example, a dose of 5 mg/kg for a 70 kg patient = 5 × 70 = 350 mg total dose. Always convert the patient's weight to the unit specified in the dosing chart (usually kg) before calculating.

Medical & Dosage Unit Converters

Q: How do I convert mcg to IU?

Like mg to IU, this conversion is substance-specific. For Vitamin D: 1 mcg = 40 IU, so 25 mcg = 1,000 IU. For Vitamin A (retinol): 1 mcg = 3.33 IU. For beta-carotene: 1 mcg = 1.67 IU. Always verify the specific substance's conversion factor before applying it.

Q: How many ml is 1 unit of insulin?

Standard insulin in the U100 concentration contains 100 units per milliliter. So 1 unit of insulin = 0.01 ml. A common insulin syringe holds 1 ml and is marked with 100 units. For U200 or U500 insulin, the concentrations differ — always check the label on your insulin vial or pen.

Q: What is the difference between mg and mcg?

1 milligram (mg) = 1,000 micrograms (mcg or µg). To convert mg to mcg, multiply by 1,000. To convert mcg to mg, divide by 1,000. Example: 0.5 mg = 500 mcg. This distinction matters greatly in medication dosing, where confusing the two units can result in a 1,000-fold dosing error.

Reference tables and conversion guides for medical units: mg to IU, mcg to IU, insulin units to ml, body-weight dosing, and more.

⚠️ Medical Disclaimer

The information on this page is for educational and reference purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider or pharmacist before making any medication decisions. Never adjust drug doses based solely on online reference materials.

Basic Medical Mass Units

The most commonly confused units in dosing. Confusing mg and mcg is a 1,000× error — the most common type of medication error.

Unit	Symbol	In grams	Convert to mg
Gram	g	1 g	× 1,000
Milligram	mg	0.001 g	× 1
Microgram	mcg / µg	0.000001 g	÷ 1,000
Nanogram	ng	0.000000001 g	÷ 1,000,000
Kilogram	kg	1,000 g	× 1,000,000

mg → mcg

Multiply by 1,000

0.5 mg = 500 mcg

mcg → mg

Divide by 1,000

250 mcg = 0.25 mg

Open Mass Converter →

Converting mg / mcg to International Units (IU)

International Units (IU) measure biological activity, not mass. The conversion factor depends on the specific substance. There is no universal "mg to IU" formula — you must use the correct factor for the compound.

Substance	1 IU equals	1,000 IU equals
Vitamin D (cholecalciferol)	0.025 mcg	25 mcg = 0.025 mg
Vitamin A (retinol)	0.3 mcg = 0.0003 mg	300 mcg = 0.3 mg
Vitamin A (beta-carotene)	0.6 mcg	600 mcg = 0.6 mg
Vitamin E (natural, d-alpha-tocopherol)	0.67 mg	670 mg
Vitamin E (synthetic, dl-alpha-tocopherol)	0.45 mg	450 mg
Heparin (approx.)	~0.002 mg	~2 mg (varies by source)

💡 Vitamin D example: A 1,000 IU Vitamin D supplement = 25 mcg = 0.025 mg. A 2,000 IU dose = 50 mcg. A 5,000 IU dose = 125 mcg.

Converting Insulin Units to mL

Insulin concentration determines the units-to-mL conversion. The most common insulin (U100) contains exactly 100 units per milliliter.

Insulin Type	Concentration	Units per mL	1 Unit = ?
U100 (standard)	100 U/mL	100	0.01 mL
U200	200 U/mL	200	0.005 mL
U300	300 U/mL	300	0.00333 mL
U500 (concentrated)	500 U/mL	500	0.002 mL

10 units U100

= 0.10 mL

20 units U100

= 0.20 mL

50 units U100

= 0.50 mL

Body-Weight Based Dosing (mg/kg)

Many medications are prescribed as mg per kilogram of body weight. To calculate: Dose (mg) = mg/kg × Weight (kg). If the patient's weight is in pounds, convert first: kg = lb ÷ 2.20462.

Patient Weight	In kg	Dose at 5 mg/kg	Dose at 10 mg/kg
110 lb	50 kg	250 mg	500 mg
132 lb	60 kg	300 mg	600 mg
154 lb	70 kg	350 mg	700 mg
176 lb	80 kg	400 mg	800 mg
198 lb	90 kg	450 mg	900 mg
220 lb	100 kg	500 mg	1,000 mg

Convert lb to kg →

Frequently Asked Questions

How do I convert mg to IU?

The mg-to-IU conversion is substance-specific. Vitamin D: 1 IU = 0.025 mcg (1,000 IU = 0.025 mg). Vitamin E (natural): 1 IU = 0.67 mg. Vitamin A (retinol): 1 IU = 0.3 mcg. There is no single universal conversion factor.

How do I convert mcg to IU?

For Vitamin D: 1 mcg = 40 IU, so 25 mcg = 1,000 IU. For Vitamin A (retinol): 1 mcg = 3.33 IU. The factor varies by substance — always verify before converting.

How many ml is 1 unit of insulin?

For standard U100 insulin: 1 unit = 0.01 mL. For U200: 1 unit = 0.005 mL. For U500: 1 unit = 0.002 mL. Always check the concentration on your insulin label.

What is the difference between mg and mcg?

1 mg = 1,000 mcg. To convert mg to mcg: multiply by 1,000. To convert mcg to mg: divide by 1,000. Example: 0.5 mg = 500 mcg. Confusing these units is one of the most common medication errors.

What does mg/kg mean in drug dosing?

mg/kg means milligrams of drug per kilogram of body weight. Total dose = mg/kg × weight in kg. For a 70 kg patient at 5 mg/kg: 5 × 70 = 350 mg total dose. If weight is in pounds, divide by 2.20462 first to get kg.

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