Every formula you need for nursing calculations on a single printable page — dosage, IV rates, infusion times, BSA and IBW, plus the conversions worth knowing by heart and the rounding rules that go with them. Built to print cleanly on one sheet for a clipboard or a folder.
| Calculation | Formula |
|---|---|
| Tablets or volume to give | (Desired ÷ Have) × Quantity |
| Weight-based dose | Dose per kg × weight in kg |
| IV flow rate | Volume (mL) ÷ time (hours) = mL/hr |
| IV drip rate | [Volume (mL) ÷ time (min)] × drop factor = gtt/min |
| Infusion duration | Volume (mL) ÷ rate (mL/hr) = hours |
| mcg/kg/min → mL/hr | (dose × kg × 60) ÷ concentration (mcg/mL) |
| Concentration | Total drug ÷ total volume |
| BSA (Mosteller) | √[(height cm × weight kg) ÷ 3600] |
| IBW (Devine, male) | 50 kg + 2.3 kg per inch over 5 ft |
| IBW (Devine, female) | 45.5 kg + 2.3 kg per inch over 5 ft |
| Unit | Equals |
|---|---|
| 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 · 3 tsp |
| 1 fl oz | 30 mL · 2 tbsp |
| 1 cup | 240 mL |
| 1 grain (gr) | 60 mg |
| 1 lb | 454 g |
| Tubing | Drop factor | Used for |
|---|---|---|
| Macrodrip | 10 gtt/mL | Large volumes, blood |
| Macrodrip | 15 gtt/mL | Standard IV fluids (US) |
| Macrodrip | 20 gtt/mL | Standard IV fluids (global) |
| Microdrip | 60 gtt/mL | Paediatric, critical drugs |
With a 60 gtt/mL microdrip set, gtt/min always equals mL/hr — the 60 drops and 60 minutes cancel out.
| Measure | Round to |
|---|---|
| Drops per minute | Whole drop |
| Tablets | Half — only if scored |
| mL (adult) | One decimal place |
| mL (paediatric) | Two decimal places |
| Pump rate | Whole mL/hr |
Stop and recheck if: the answer needs more than about 3 tablets, less than a quarter tablet, an IM injection over 3 mL, a drip rate too fast to count, or a dose far outside the drug's usual range. These are arithmetic errors, not unusual prescriptions.
Desired divided by Have, multiplied by Quantity (D/H x Q). For an order of 500 mg where stock is 250 mg in 5 mL, that is 500 divided by 250, multiplied by 5, which equals 10 mL. Both values must be in the same unit before dividing.
Volume in mL divided by time in minutes, multiplied by the drop factor of the tubing in drops per mL. For 1,000 mL over 8 hours on a 15 gtt/mL set: 1,000 divided by 480 minutes, multiplied by 15, gives 31 drops per minute.
There are 1,000 micrograms in 1 milligram and 1,000 milligrams in 1 gram. To convert mg to mcg multiply by 1,000; to convert mcg to mg divide by 1,000.