Drug Dose Unit Conversions
Medication dosing errors are among the most common, and preventable, causes of patient harm in healthcare settings. Understanding drug dose units and the relationships between them is a foundational skill for nurses, pharmacists, and prescribers.
Mass Unit Relationships
| Unit | Abbreviation | Equivalent |
|---|---|---|
| Gram | g | 1,000 mg = 1,000,000 mcg |
| Milligram | mg | 0.001 g = 1,000 mcg |
| Microgram | mcg or µg | 0.001 mg = 1,000 ng |
| Nanogram | ng | 0.001 mcg = 0.000001 mg |
This converter handles pure mass units only (g, mg, mcg, ng). It deliberately does not offer mEq or mmol conversion: unlike mass units, milliequivalents and millimoles depend on a specific drug's molecular weight and ionic valence, so a single universal conversion factor would be wrong for every substance except the one it was calculated for. For potassium chloride, sodium bicarbonate, calcium gluconate, and similar electrolytes, use the concentration printed on the product label or your pharmacy reference, a generic mg-to-mEq conversion cannot be done safely without knowing the specific salt.
Weight-Based Dosing
Many drugs are prescribed as mg/kg (milligrams per kilogram of body weight) to account for differences in pharmacokinetics across body sizes. The total dose = prescribed dose per kg × patient weight. For obese patients, confirm whether actual, ideal, or adjusted body weight should be used, this varies by drug class. See the Ideal Body Weight Calculator for the standard reference formulas.
Infusion Rate Conversions
IV infusion rates can be expressed in multiple ways: mL/hr (for pump programming), mg/hr or mcg/hr (total drug per hour), mcg/min (common for vasopressors), or mcg/kg/min (weight-based infusions). All are mathematically interconvertible given the drug concentration in the bag. The calculator above outputs its result in whichever unit you select for the bag's contents, it does not silently convert between mg and mcg, so select "mcg in bag" if you want a mcg/min result. As a worked example: a bag containing 400 mg in 250 mL, run at 15 mL/hr, gives a concentration of 1.6 mg/mL and a rate of 0.4 mg/min; to express that as mcg/min instead, multiply by 1000 to get 400 mcg/min, or re-enter the bag concentration as 400,000 mcg in 250 mL. For a dedicated drop-rate and mcg/kg/min calculator, see our IV Drip Rate Calculator.
High-Alert Medications
The Institute for Safe Medication Practices (ISMP) High-Alert Medications list identifies several drugs where dose calculation errors can cause serious harm: concentrated electrolytes (KCl, NaCl), insulin, heparin/LMWH, opioids, chemotherapy agents, and concentrated vasoactives. Independent double-check of calculations is required for these drugs in most hospital protocols.