Dosage Calculation Formulas
Every formula CARE's calculators and practice problems use, with the unit logic for each.
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Dosage Calculation Formulas
Core formulas
These are the same formulas the CARE calculators apply — one definition, used everywhere.
| Dosage math (desired over have) | Desired ÷ Have × QuantityThe general formula behind most oral and injectable dose problems. |
|---|---|
| Tablets or capsules | Desired ÷ Strength per tablet = number of tabletsHow many tablets supply an ordered amount from a given tablet strength. |
| Liquid medication volume | (Desired ÷ Strength) × Volume that strength is in = millilitresHow many millilitres supply an ordered amount from a stated concentration. |
| Weight-based amount | Weight in kg × amount per kg = total amount (lb ÷ 2.2 = kg)The total amount an ordered rate per kilogram works out to, with a pounds conversion if needed. |
| IV flow rate (mL/hr) | Total volume ÷ time in hours = mL/hrThe pump rate for a volume that has to run over a set time. |
| IV drip rate (gtt/min) | (Volume × drop factor) ÷ time in minutes = gtt/minDrops per minute for gravity tubing with a known drop factor. |
| IV infusion time | Total volume ÷ rate = infusion time in hoursHow long a volume takes at a set rate. |
Metric conversions used in dose math
| 1 gram (g) | 1,000 milligrams (mg) |
|---|---|
| 1 milligram (mg) | 1,000 micrograms (mcg) |
| 1 kilogram (kg) | 1,000 grams — and 2.2 pounds |
| 1 litre (L) | 1,000 millilitres (mL) |
Rounding
| Drops per minute | Whole numbersYou cannot count part of a drop. |
|---|---|
| Pump rate (mL/hr) | Whole numbersThat is how a pump is set. |
| Tablets | Whole or half onlyA result that is neither usually means the numbers need re-checking, or the form cannot be split. |
| Everything else | Follow your program or facility ruleRounding rules are set locally; there is no single universal rule. |
Educational reference. Verify medication calculations against your program, facility policy, the actual order, and any independent check your policy requires.