Nursing Calculation Resources

Divide pounds by 2.2. For example, a 154 lb patient weighs 70 kg (154 ÷ 2.2 = 70). This is the most fundamental conversion in nursing — you’ll use it for nearly every weight-based dosage calculation.

Macrodrip tubing has larger drops (10, 15, or 20 gtts/mL) and is used for larger-volume infusions like NS or LR. Microdrip tubing has 60 gtts/mL (tiny drops) and is used for precise, small-volume infusions like pediatric medications or KVO rates.

Use the formula: (Volume in mL × Drop Factor) ÷ Time in minutes = gtts/min. For example, 1000 mL over 8 hours with 20 gtts/mL tubing: (1000 × 20) ÷ 480 = 41.7, rounded to 42 gtts/min.

Dimensional analysis is a method of solving calculation problems by multiplying conversion factors so units cancel out, leaving only the desired unit. Use it for ANY dosage calculation — it’s the safest, most reliable method recommended by Kaplan, UWorld, and most nursing programs.

Formula: (Dose in mcg/kg/min × Weight in kg × 60) ÷ Concentration in mcg/mL = mL/hr. First convert the drug concentration to mcg/mL (mg × 1000 ÷ volume mL), then plug in the values.

Calculate the mg/kg dose from the order, look up the drug’s safe range in a reference, and verify the ordered dose falls between the minimum and maximum. If it’s outside the range, hold the medication and call the provider before administering.

Essential: 1 kg = 2.2 lb, 1 g = 1000 mg, 1 mg = 1000 mcg, 1 L = 1000 mL, 1 oz = 30 mL, 1 tsp = 5 mL, 1 tbsp = 15 mL. These appear in virtually every nursing dosage calculation.

Round to the nearest tenth for most medications. For IV drip rates, round to the nearest whole number (you can’t count partial drops). For pediatric doses, always round DOWN to avoid overdosing. Never round tablet doses to more than the scored divisions allow.

It’s a ratio expressing concentration. 1:1000 means 1 g per 1000 mL = 1 mg/mL (used for IM injection, anaphylaxis). 1:10,000 means 1 g per 10,000 mL = 0.1 mg/mL (used for IV push in cardiac arrest). Confusing these can be fatal.

Time (hours) = Volume (mL) ÷ Rate (mL/hr). For example, a 1000 mL bag running at 125 mL/hr will last 1000 ÷ 125 = 8 hours. You’ll need this to plan bag changes and answer patient questions.

Use the Mosteller formula: BSA (m²) = √(Height in cm × Weight in kg ÷ 3600). For example, a patient 170 cm tall and 70 kg: BSA = √(170 × 70 ÷ 3600) = √(3.31) = 1.82 m². This is used primarily in oncology and pediatrics.

mg/mL is the concentration of drug in the IV fluid (how much drug per mL of fluid). mL/hr is the infusion rate (how fast the fluid is running). You use the concentration to convert a dose order (mg or mcg) into a pump rate (mL/hr).