Nursing Dosage Calculations Workbook – Formulas, IV Drips & Practice Problems

Nursing Dosage Calculations Workbook:
Formulas, IV Drips, and Practice
Problems

1. Core Formulas for Medication Calculations
1.1 Basic Dose Formula

Desired Dose
Dose to Administer = × Quantity Available
Available Dose


Example:

• Order: 250 mg of medication
• Available: 500 mg tablets

250
Dose to Administer = × 1 = 0.5 tablet
500



1.2 IV Flow Rate Formulas

1. Volume (mL) per Time (hr):

Total Volume (mL)
Flow Rate (mL/hr) =
Time (hr)


2. Drops per Minute:

Volume (mL) × Drop Factor (gtt/mL)
gtt/min =
Time (min)

,Example:

• IV: 1000 mL NS over 8 hr
• Drop factor: 15 gtt/mL

1000
Flow rate = = 125 mL/hr
8
1000 × 15
gtt/min = ≈ 31 gtt/min
480



1.3 Pediatric Dose Calculation

Weight (kg) × Adult Dose
Child’s Dose =
70 kg



1.4 Body Surface Area (BSA) Method

BSA (m²)
Child’s Dose = × Adult Dose
1.73


BSA formula (Mosteller):

Height (cm) × Weight (kg)
BSA = √
3600



1.5 IV Piggyback (Secondary) Rate

Volume of Medication
Flow Rate (mL/hr) = + Primary IV Rate (if combined)
Time (hr)

, 2. Common Unit Conversions
Conversion Value
1 mg = ? g 0.001 g
1 g = ? mg 1000 mg
1 kg = ? g 1000 g
1 mL = ? L 0.001 L
1 tsp = ? mL 5 mL
1 tbsp = ? mL 15 mL
1 oz = ? mL 30 mL
1 lb = ? kg 0.45 kg


3. Step-by-Step Examples
Example 1: Tablet Dose Calculation

• Order: 75 mg
• Available: 50 mg tablets

75
Dose to Administer = × 1 = 1.5 tablets
50


Example 2: IV Drip Rate

• IV: 500 mL over 4 hours
• Drop factor: 20 gtt/mL

500 × 20 10000
gtt/min = = ≈ 42 gtt/min
4 × 60 240


Example 3: Pediatric Dose

• Adult dose: 500 mg
• Child weight: 20 kg