Drug calculations.
Make the math make sense.
Convert the units. Set up the problem. Check your answer. Build your dosage-calculation skills with clear formulas, worked examples, and a 15-question practice quiz.
× Quantity
Match the dose units first. Keep units in your work. Round the final answer as instructed.
Start with the units.
A dose is the amount of medication. A concentration tells you how much medication is in a given volume or quantity. A rate tells you how quickly it is delivered.
Read the label
250 mg per 5 mL means each 5 mL contains 250 mg. The concentration is 50 mg/mL. It does not mean 250 mg in every 1 mL.
Read the question
Are you solving for tablets, mL per dose, mL/hr, gtt/min, or medication delivered per minute? Write that target unit before you calculate.
| Equivalent | How to convert |
|---|---|
| 1 g = 1,000 mg | g → mg: × 1,000. mg → g: ÷ 1,000. |
| 1 mg = 1,000 mcg | mg → mcg: × 1,000. mcg → mg: ÷ 1,000. |
| 1 L = 1,000 mL | L → mL: × 1,000. mL → L: ÷ 1,000. |
| 1 kg ≈ 2.2 lb | For these practice problems: lb → kg: ÷ 2.2. |
| 1 hr = 60 min | Hours → minutes: × 60. Minutes → hours: ÷ 60. |
| 1 unit = 1,000 milliunits | Units → milliunits: × 1,000. Milliunits → units: ÷ 1,000. |
| 1 teaspoon = 5 mL; 1 tablespoon = 15 mL | Medication-learning equivalents. Measure oral liquids with a calibrated mL device, not a kitchen spoon. |
| 1 US fluid ounce ≈ 30 mL; 1 US cup ≈ 240 mL | Common nursing approximations for intake calculations; not exact metric equivalents. |
Keep the notation clear. Write mL, mcg, units, and milliunits. Use a leading zero (0.5 mg) and no trailing zero (5 mg). A medication’s units describe its activity; units cannot be converted to mg without a product-specific relationship. Grain conversions are legacy conventions—use the stated factor if a course question includes them.
Common order terms: what they mean
| Term | Meaning |
|---|---|
| PO / IM / IV / SL | By mouth / intramuscular / intravenous / sublingual |
| Subcutaneous / intradermal | Routes of injection; write the route clearly. |
| IV push / IVPB | IV administration over a medication-specific push time / IV piggyback infusion |
| AC / PC | Before meals / after meals; times depend on the actual meal schedule. |
| BID / TID / QID | Twice / three times / four times daily. These do not automatically mean every 12 / 8 / 6 hours. |
| Every 6 hours | An interval order; an around-the-clock schedule gives 4 doses in 24 hours. |
| PRN / STAT | As needed, with the ordered indication and limits / immediately |
| Daily / at bedtime | Once daily / at bedtime; follow the prescribed schedule. |
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- ✓ Conversions, formulas & rounding rules
- ✓ Worked examples from tablets to titrated drips
- ✓ A 15-question practice quiz with rationales
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