⚠️ Not medical advice
This page explains dosage units for education only. It is not a substitute for professional medical guidance. International Units (IU) are substance-specific, and dosing errors can be harmful or fatal. Always follow your prescriber’s instructions and confirm any conversion with a pharmacist or physician.
Medical Dosage Unit Converters
Understand the units behind medication labels: why IU-to-mg changes by substance, the exact mg-to-mcg relation, and standard drop-to-mL factors. Use it to read labels — never to set your own dose.
Direct answer
- • 1 mg = 1,000 mcg (exact, any substance).
- • IU is substance-specific — e.g., vitamin D 1 IU = 0.025 mcg; insulin 1 IU = 0.0347 mg.
- • 1 mL ≈ 20 drops (standard macrodrip); 1 drop ≈ 0.05 mL.
- • 1 US tsp = 4.92892 mL; 1 US tbsp = 14.7868 mL (exact US customary).
Exact mass relations (any substance)
| From | To | Factor |
|---|---|---|
| 1 gram (g) | milligram (mg) | 1,000 (exact) |
| 1 milligram (mg) | microgram (mcg) | 1,000 (exact) |
| 1 kilogram (kg) | gram (g) | 1,000 (exact) |
IU reference — substance-specific (verify per product)
| Substance | Approx. IU → mass | Note |
|---|---|---|
| Vitamin D | 1 IU = 0.025 mcg (40 IU = 1 mcg) | Widely standardized |
| Vitamin A (retinol) | 1 IU = 0.3 mcg | Beta-carotene differs |
| Vitamin E (natural d-α) | 1 IU = 0.67 mg | Synthetic differs |
| Human insulin | 1 IU = 0.0347 mg (1 mg = 28.8 IU) | Biologic standard |
| Heparin | ≈ 1 mg = 130 IU | Preparation dependent |
These are published reference values, not a universal rule. The same “IU” can mean different masses for different drugs and even different formulations of the same drug. Always read the product label and ask a pharmacist.
Volume & drops
| From | To | Factor |
|---|---|---|
| 1 US teaspoon | mL | 4.92892 (exact US) |
| 1 US tablespoon | mL | 14.7868 (exact US) |
| 1 mL (macrodrip) | drops (gtt) | 20 (set dependent) |
| 1 mL (microdrip) | drops (gtt) | 60 (set dependent) |
How to read a label safely
Mass units (g, mg, mcg) convert exactly and safely between each other.
IU never converts to mass without knowing the exact substance and formulation — check the label’s “IU = mg” statement.
Drops are not a reliable dose; use a calibrated oral syringe and the stated concentration (e.g., mg/mL).
Frequently Asked Questions
Why can’t I use one IU-to-mg number for everything?
An International Unit (IU) measures biological activity, not mass, so its mg equivalent is different for every substance. For example, 1 IU of vitamin D = 0.025 mcg, but 1 IU of vitamin E (natural) = 0.67 mg. Never assume one conversion applies across drugs or supplements.
How many micrograms are in a milligram?
Exactly 1,000. The relation 1 mg = 1,000 mcg (and 1 g = 1,000 mg) is a fixed metric definition with no substance dependence — safe to use for any compound.
How many mL is one drop?
A standard macrodrip set delivers 20 drops (gtt) per mL, so 1 drop ≈ 0.05 mL. Microdrip sets use 60 gtt/mL. Dropper calibration varies, so for medication never rely on “drops” — use a marked oral syringe and the product’s stated concentration.
Can I use this to convert my prescription dose?
No. This page is educational only and is not medical advice. Dosing errors can be harmful or fatal. Always follow your prescriber’s instructions and confirm any unit conversion with a pharmacist or physician.
Related Converters
Sources & Accuracy
Exact US customary volume factors (1 tsp = 4.92892 mL, 1 tbsp = 14.7868 mL) are from NIST SP 330. The mg↔mcg and g↔mg relations are fixed SI definitions.
IU reference values are published substance standards (e.g., NIH Office of Dietary Supplements for vitamin D; pharmacopeia monographs for insulin, heparin, vitamins). They are substance- and formulation-specific — always confirm on the product label.
Volume definitions: NIST SP 330 (SI). Vitamin D: NIH ODS — Vitamin D.
Last Updated 2026 | Educational reference only — not medical advice; verify all doses with a licensed professional