Dosage Calculation and Unit Conversion

Flashcards covering essential dosage calculation formulas, metric and household conversions, IV flow rate math, and nursing rounding rules.

Core Dosage Calculation Formula

$\frac{D}{H} \times Q = \text{Amount to give}$, where $D$ is the desired dose, $H$ is the dose on hand, and $Q$ is the quantity containing the dose on hand.

D (in Dosage Calculations)

Desired (the ordered dose).

H (in Dosage Calculations)

Dose on hand (the dosage strength available).

Q (in Dosage Calculations)

Quantity containing the dose on hand (volume or unit like tablets/mL).

1 kg (Metric conversion to g)

$$1,000\,g$$

1 g (Metric conversion to mg)

$$1,000\,mg$$

1 mg (Metric conversion to mcg)

$$1,000\,mcg$$

1 L (Metric conversion to mL)

$$1,000\,mL$$

1 mL (Metric conversion to cc)

$$1\,cc$$

1 kg (Weight conversion to lb)

$$2.2\,lb$$

1 tsp (Household conversion)

$$5\,mL$$

1 Tbsp (Household conversion)

$$15\,mL$$

1 oz (Nursing household conversion)

$$30\,mL$$

1 cup (Household conversion)

$$8\,oz = 240\,mL$$

1 pint (Household conversion)

$$16\,oz = 480\,mL$$

1 quart (Household conversion)

$$32\,oz = 960\,mL$$

Metric Shortcut: Large unit to smaller unit

Multiply by $1,000$ (e.g., $0.5\,g \times 1,000 = 500\,mg$).

Metric Shortcut: Small unit to larger unit

Divide by $1,000$ (e.g., $250\,mg / 1,000 = 0.25\,g$).

Safe Dose Range Calculation

A process where you 1) Convert weight to kg, 2) Find the minimum and maximum safe dose, and 3) Compare the ordered dose with that range.

IV Flow Rate (mL/hr) Formula

$$\text{total mL} / \text{hours}$$

IV Flow Rate (gtt/min) Formula

$$\frac{\text{mL} \times \text{drop factor}}{\text{minutes}}$$

U-100 Insulin

A specific concentration meaning $100\,\text{units/mL}$; use the exact concentration supplied in the question.

Rounding Rule for Liquid Oral Meds

Commonly round to the nearest tenth if $> 1\,mL$ and to the nearest hundredth if $< 1\,mL$ when appropriate.

Rounding Rule for IV Flow Rates

Commonly round to the nearest whole $mL/hr$ for IV pumps and to the nearest whole number for drops (gtt/min).

Weight-Based Dose Calculation Steps

1) Convert $lb$ to $kg$ ($lb / 2.2$), 2) Calculate ordered dose ($mg/kg \times kg$), 3) Use $D/H \times Q$ formula.