Module 6 of 7
Dosage Calculations
Strength vs. Dose — Know the Difference
| Term | Definition | Example |
|---|---|---|
| Strength (S) | How STRONG each individual tablet, patch, or liquid concentration is (usually in mg per tablet or mg per mL) | Metformin 500mg tablet = strength is 500mg per tablet |
| Dose (D) | The AMOUNT of medication the physician's order tells you to GIVE the client | Physician order: "Take 1000mg" = dose is 1000mg |
Strength and dose are NOT the same thing. Strength is what's in each unit; Dose is what the doctor ordered to give.
The Dose Math Formula — Solid Medications
Dose ÷ Strength = Number of Tablets (or capsules) to Give
Memory tip: What you Need (Dose) ÷ What you Have (Strength) = What you Give
Example 1
Label: Lasix 10mg tablets | Order: Give 40mg
40 ÷ 10 = 4 tablets
✓ You will give 4 tablets
Example 2
Label: Trazodone 100mg scored tablets | Order: Give 50mg
50 ÷ 100 = ½ tablet
✓ You will give ½ of a scored tablet (only with a written order permitting splitting)
Example 3
Label: Depakote 125mg spansules | Order: Give 375mg
375 ÷ 125 = 3 capsules
✓ You will give 3 spansule capsules
The Dose Math Formula — Liquid Medications
(Dose ÷ Strength) × Volume = mL to Give
Example 1
Amoxicillin 250mg/5mL | Order: Give 500mg
(500 ÷ 250) × 5 = 2 × 5 = 10 mL
✓ You will give 10 mL (2 teaspoons)
Example 2
Give 50mg of a liquid medication. Bottle reads 5mg/cc.
(50 ÷ 5) × 1cc = 10 cc
✓ You will give 10 cc (10 mL)
Metric Equivalencies — The Chant: 5 · 15 · 30
Memorize these equivalencies — they appear frequently on the QMAP test:
5 – 15 – 30 | t – T – O
| Household | Metric | Notes |
|---|---|---|
| 1 teaspoon (tsp) | 5 mL | Also written as 5 cc |
| 1 Tablespoon (Tbsp) | 15 mL | = 3 teaspoons |
| 1 ounce (oz) | 30 mL | = 2 Tablespoons = 6 teaspoons |
| 1 cc | = 1 mL | Used interchangeably |
Dry Measure Equivalencies
| Unit | Equivalent |
|---|---|
| 1,000 mg (milligrams) | = 1 Gm (gram) |
| 1,000 mL | = 1 Liter |
| 1 cc | = 1 mL |
Practice Conversions
3 tsp = ? Tbsp = ? cc
3 tsp = 1 Tbsp = 15 cc ✓
2 Tbsp = ? cc = ? oz
2 Tbsp = 30 cc = 1 oz ✓
You need 1 ounce of Milk of Magnesia. How many cc?
1 oz = 30 cc ✓
Reading Medication Labels
Every medication label must contain the 5 Rights (Person, Drug, Dose, Route, Time). Additional information you will find on a pharmacy label:
- Client's name (Right Person)
- Drug name — brand and/or generic (Right Drug)
- Strength (e.g., 500mg tablet)
- Dose instructions (e.g., "Take 2 tablets by mouth daily")
- Route (Right Route)
- Frequency and schedule (Right Time)
- Prescribing physician name
- Pharmacy name and phone number
- Prescription number
- Date filled and expiration date
- Number of refills
- Any special instructions (e.g., "Take with food," "Shake Well")
Critical Rule: Always compare the pharmacy label to the physician's order AND the MAR before administering. If anything does not match, DO NOT administer the medication — contact the pharmacist or physician to resolve the discrepancy first.
Measuring Tools
| Tool | Use | Notes |
|---|---|---|
| Measuring spoon (baking spoon) | Small liquid doses | Acceptable but least accurate |
| Graduated dropper | Very small liquid amounts | Has both metric and apothecary markings |
| Dosing spoon | 5–10 mL liquid | Convenient shape; can be washed and reused by same client |
| Measured medication cup | Larger liquid volumes | Has both metric and household measures; read at eye level |
| Syringe | Precise small volumes | Read at eye level; each line = 0.2 cc on 5cc syringe; 0.1 on 3cc syringe |
Measurement Rule: Always measure liquids at eye level. Never approximate — inaccurate measurement is a medication error.
📝 Module 6 Quiz
Answer all 6 questions. You need 85% or higher to complete this module.