The drug unit converter converts between the metric units used in drug prescriptions and pharmacology: grams (g), milligrams (mg), micrograms (mcg/μg), and nanograms (ng). Unit confusion — particularly between milligrams and micrograms — is one of the most common and dangerous sources of medication errors, representing a 1000-fold dosing difference. Use this converter to verify unit conversions before drawing up any medication.
| From | To | Multiply by |
|---|---|---|
| g | mg | × 1,000 |
| mg | mcg | × 1,000 |
| mcg | ng | × 1,000 |
| mg | g | ÷ 1,000 |
| mcg | mg | ÷ 1,000 |
| kg | lb | × 2.20462 |
| lb | kg | ÷ 2.20462 |
To convert mg to mcg, multiply by 1,000. The most commonly prescribed strengths are shown below.
| Milligrams (mg) | Micrograms (mcg) |
|---|---|
| 0.05 mg | 50 mcg |
| 0.1 mg | 100 mcg |
| 0.125 mg | 125 mcg |
| 0.2 mg | 200 mcg |
| 0.25 mg | 250 mcg |
| 0.5 mg | 500 mcg |
| 0.75 mg | 750 mcg |
| 1 mg | 1,000 mcg |
| 1.5 mg | 1,500 mcg |
| 2 mg | 2,000 mcg |
| 2.5 mg | 2,500 mcg |
| 5 mg | 5,000 mcg |
| 10 mg | 10,000 mcg |
To convert mcg to mg, divide by 1,000.
| Micrograms (mcg) | Milligrams (mg) |
|---|---|
| 25 mcg | 0.025 mg |
| 50 mcg | 0.05 mg |
| 100 mcg | 0.1 mg |
| 125 mcg | 0.125 mg |
| 200 mcg | 0.2 mg |
| 250 mcg | 0.25 mg |
| 400 mcg | 0.4 mg |
| 500 mcg | 0.5 mg |
| 750 mcg | 0.75 mg |
| 1,000 mcg | 1 mg |
Unit equivalents for strengths often written on labels and orders. This is a unit-conversion reference only — always dose exactly as prescribed and verify against the label.
| Written as | Same as |
|---|---|
| 0.125 mg | 125 mcg |
| 0.25 mg | 250 mcg |
| 0.05 mg | 50 mcg |
| 0.1 mg | 100 mcg |
| 1 mg | 1,000 mcg |
| 500 mg | 0.5 g |
| 1,000 mg | 1 g |
| 250 mg | 0.25 g |
Milliequivalents (mEq) cannot be converted to milligrams with a single factor — the value depends on the specific salt and its molecular weight. Below are the standard equivalents for the IV electrolyte salts nurses handle most often.
| Salt | 1 gram provides | 1 mEq equals |
|---|---|---|
| Potassium chloride (KCl) | ≈ 13.4 mEq K⁺ | ≈ 74.6 mg |
| Sodium chloride (NaCl) | ≈ 17.1 mEq Na⁺ | ≈ 58.4 mg |
| Sodium bicarbonate (NaHCO₃) | ≈ 11.9 mEq | ≈ 84 mg |
| Magnesium sulfate (MgSO₄·7H₂O) | ≈ 8.1 mEq Mg²⁺ | ≈ 123 mg |
| Calcium gluconate | ≈ 4.65 mEq Ca²⁺ | ≈ 215 mg |
Household measures turn up constantly in home-care instructions and on liquid medication labels, and they're tested throughout nursing school. These are the standard clinical equivalents — worth committing to memory, because they appear in almost every conversion question you'll meet.
| Household unit | Metric equivalent | Also equals |
|---|---|---|
| 1 teaspoon (tsp) | 5 mL | 60 drops (gtt) |
| 1 tablespoon (tbsp) | 15 mL | 3 teaspoons |
| 1 fluid ounce (fl oz) | 30 mL | 2 tablespoons |
| 1 cup | 240 mL | 8 fluid ounces |
| 1 pint | 480 mL | 2 cups |
| 1 quart | 960 mL | 2 pints |
| 1 pound (lb) | 454 g | 16 ounces |
| 2.2 pounds | 1 kilogram | — |
A safety note that matters more than the arithmetic: household spoons are not measuring devices. A "teaspoon" from a cutlery drawer can hold anywhere from about 3 to 7 mL, which is a meaningful error on a paediatric dose. Liquid medication should be measured with an oral syringe or the dosing cup supplied, and patients should be told so explicitly.
The apothecary system is largely historical and rarely used in modern prescribing, but it still appears on the NCLEX and occasionally on older orders — grains being the one you're most likely to meet, since some medications are still labelled that way.
| Apothecary unit | Metric equivalent |
|---|---|
| 1 grain (gr) | 60 mg |
| 5 grains | 300–325 mg |
| 10 grains | 600–650 mg |
| 15 grains | 1 g |
| 1 minim | ≈ 1 drop |
| 1 fluid dram | 4–5 mL |
Apothecary notation puts the unit before the amount and uses lower-case Roman numerals, so 4 grains is written gr iv rather than 4 gr. Because 1 grain is 60 mg, the familiar 325 mg aspirin tablet is the old 5-grain tablet in metric dress.
If you learn nothing else from this page, learn these. They cover the overwhelming majority of conversion questions in both nursing school and practice:
| Core conversions | |
|---|---|
| 1 kg | 1,000 g · 2.2 lb |
| 1 g | 1,000 mg |
| 1 mg | 1,000 mcg |
| 1 L | 1,000 mL |
| 1 tsp | 5 mL |
| 1 tbsp | 15 mL |
| 1 oz | 30 mL |
| 1 gr | 60 mg |
| 1 lb | 454 g |
And the rule that sits above all of them: if you aren't certain of a conversion factor, look it up. Never prepare or give a medication on a conversion you're guessing at — the two seconds it takes to check is the cheapest safety measure in the job.
There are 1,000 micrograms (mcg) in 1 milligram (mg). This is one of the most important conversions in nursing — mistaking mg for mcg results in a 1000-fold overdose. Always double-check the unit on the drug label before administration.
There are 1,000 milligrams (mg) in 1 gram (g). The full metric chain is: 1 g = 1,000 mg = 1,000,000 mcg = 1,000,000,000 ng.
0.5 mg equals 500 mcg. To convert milligrams to micrograms, multiply by 1,000: 0.5 × 1,000 = 500 mcg. Common examples: 0.25 mg = 250 mcg, and 0.125 mg = 125 mcg (a typical digoxin dose).
No. International units (IU or "units") measure biological activity, not mass, so they cannot be converted to milligrams with a fixed factor. The relationship is drug-specific — insulin units and heparin units each have their own definition. Always dose these medications in units, exactly as prescribed, and never substitute a mg value.