Oral and Liquid Medication Dosage Calculation: Tablets, Capsules, and Solutions

1) Tablet and Capsule Problems

1.1 Ordered dose vs. available strength (single unit)

For solid oral meds, the label usually states a strength per tablet/capsule (e.g., 250 mg per tablet). Your job is to match the ordered dose to the available strength and determine how many tablets/capsules to administer.

Core setup:

Number of tablets (or capsules) = Ordered dose (mg) ÷ Strength per tablet (mg/tablet)

Example: Order: amoxicillin 500 mg PO now. Available: 250 mg capsules.

Capsules = 500 mg ÷ (250 mg/capsule) = 2 capsules

1.2 Handling multiple tablets (non-matching strengths)

Sometimes the ordered dose does not match a single tablet strength, and you may need multiple tablets of the same strength.

Example: Order: metoprolol 75 mg PO daily. Available: 25 mg tablets.

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Tablets = 75 mg ÷ (25 mg/tablet) = 3 tablets

If multiple strengths are stocked (e.g., 25 mg and 50 mg), follow facility policy and prescriber/pharmacy guidance. Do not “mix and match” strengths unless it is allowed and available in your medication system.

1.3 Splitting tablets (half-tablets and scored tablets)

Tablet splitting is only appropriate when the tablet is scored and splitting is permitted by policy and the medication’s formulation. Do not split enteric-coated, extended-release, or otherwise “do not crush/split” formulations.

Example (half-tablet): Order: 12.5 mg PO. Available: 25 mg scored tablet.

Tablets = 12.5 mg ÷ (25 mg/tablet) = 0.5 tablet

Example (quarter-tablet): Order: 6.25 mg PO. Available: 25 mg scored tablet.

Tablets = 6.25 mg ÷ 25 mg/tablet = 0.25 tablet

Quartering is often less accurate than halving. If the ordered dose requires quartering, verify whether an alternate strength or liquid formulation is available, and follow policy.

1.4 Quick reasonableness checks for tablets/capsules

• If the ordered dose is greater than the strength per tablet, you should get a number > 1.
• If the ordered dose is less than the strength per tablet, you should get a number < 1 (often 0.5 if a half-tablet is intended).
• Confirm the route and dosage form match the order (tablet vs. capsule vs. ODT, etc.).

2) Liquid Oral Solutions and Suspensions

Liquid oral medications are commonly labeled as a concentration, either mg per mL or mg per 5 mL. You may be given an order in mg (and you must calculate mL), or an order in mL (and you must determine mg delivered).

2.1 Ordered mg with concentration in mg/mL (calculate mL to administer)

When the label provides mg/mL, calculate volume directly:

mL to give = Ordered dose (mg) ÷ Concentration (mg/mL)

Example: Order: morphine oral solution 6 mg PO. Available: 2 mg/mL.

mL = 6 mg ÷ (2 mg/mL) = 3 mL

2.2 Ordered mg with concentration in mg/5 mL (calculate mL to administer)

Many pediatric and antibiotic suspensions are labeled as mg per 5 mL. Convert it to a proportion:

mL to give = Ordered dose (mg) × (5 mL ÷ mg in 5 mL)

Example: Order: acetaminophen 240 mg PO. Available: 160 mg/5 mL.

mL = 240 mg × (5 mL ÷ 160 mg) = 7.5 mL

2.3 Ordered mL with concentration in mg/5 mL (calculate mg delivered)

Sometimes the order is volume-based (common with standing PRN orders). If you must document mg given, compute:

mg delivered = Ordered volume (mL) × (mg in 5 mL ÷ 5 mL)

Example: Order: give 10 mL of ibuprofen suspension. Available: 100 mg/5 mL.

mg = 10 mL × (100 mg ÷ 5 mL) = 10 × 20 mg = 200 mg

2.4 Suspensions: “shake well” and reconstitution awareness

Suspensions require mixing to ensure the concentration is uniform. If the label indicates Shake well, do so before measuring. If the product is reconstituted (powder + diluent), the concentration depends on correct reconstitution and final volume; verify the label’s final concentration after reconstitution (e.g., “after reconstitution, each 5 mL contains…”).

3) Re-checks for Safety and Accuracy

3.1 Maximum single dose considerations

Before administering, compare the ordered dose to common safe limits and the patient’s situation (age, renal/hepatic function, comorbidities). If the order appears unusually high for a single dose, pause and verify per policy (check MAR, order details, pharmacy, prescriber). This is a clinical safety check in addition to the math.

Practical approach:

• Confirm you are using the correct formulation (immediate-release vs. extended-release; adult vs. pediatric concentration).
• Confirm timing (single dose vs. total daily dose).
• Confirm whether the order is weight-based elsewhere in the chart (especially pediatrics).

3.2 Measurement device selection: med cup vs. oral syringe

Select the device that best matches the volume and required accuracy.

Technique reminder: Measure liquids at eye level on a flat surface (med cup) or read the syringe at the correct plunger edge per device design.

3.3 Labeling details that affect administration

• Shake well: required for suspensions to ensure correct concentration.
• Reconstitution notes: verify the final concentration and beyond-use date after mixing.
• Storage: some reconstituted antibiotics require refrigeration; storage affects stability.
• Directions: “take with food,” “do not crush,” or “measure with oral syringe” may appear on pharmacy labels.

4) Rounding and Reporting

4.1 Rounding for tablets/capsules

• Tablets are typically administered as whole or half tablets when appropriate.
• If your calculation yields an impractical fraction (e.g., 0.33 tablet), do not guess—verify if a different strength or formulation is needed.
• Capsules are generally not split; if the dose does not match capsule strength, verify alternatives.

4.2 Rounding for oral liquids

Round volumes to a precision that matches the measuring device and policy. Common practice is to round to the nearest 0.1 mL when using an oral syringe that has 0.1 mL markings, and to the nearest 0.5–1 mL when using a med cup (depending on cup markings). Always align rounding with what you can accurately measure.

Examples:

• Calculated 7.46 mL → measure 7.5 mL (if rounding to nearest 0.1 or 0.5 per policy/device).
• Calculated 2.03 mL → measure 2.0 mL (if rounding to nearest 0.1 mL).

4.3 How to document dose given and volume measured

Document what you actually administered, using units clearly:

• Tablets/capsules: “Administered 2 tablets (total 500 mg) PO.”
• Liquids: “Administered 7.5 mL PO (240 mg) using oral syringe.”

If your MAR requires both mg and mL, calculate and record both. If only one is required, still ensure your calculation supports the administered amount.

5) Practice Scenarios (Labels Described in Text)

For each scenario, read the order and the label description. Calculate the final answer and include units. Assume standard oral administration unless otherwise stated.

Scenario 1: Ordered dose vs. tablet strength

Provider order: Levothyroxine 50 mcg PO daily.

Label (described): Bottle reads “Levothyroxine tablets, 25 mcg per tablet. Dispense: 30 tablets. Directions: Take 1 tablet by mouth daily.”

Calculate: How many tablets will you administer for a 50 mcg dose?

Answer: 2 tablets

Scenario 2: Splitting a scored tablet

Provider order: Lisinopril 5 mg PO now.

Label (described): Blister pack reads “Lisinopril 10 mg tablets (scored).”

Calculate: How many tablets will you administer?

Answer: 0.5 tablet

Scenario 3: Multiple tablets required

Provider order: Calcium carbonate 1500 mg PO once.

Label (described): Bottle reads “Calcium carbonate 500 mg tablets.”

Calculate: How many tablets will you administer?

Answer: 3 tablets

Scenario 4: Liquid concentration in mg/mL (ordered mg)

Provider order: Diphenhydramine 12.5 mg PO.

Label (described): Oral solution reads “Diphenhydramine 12.5 mg/5 mL. Total volume 118 mL. Directions: Take as directed.”

Calculate: How many mL will you administer?

Work:

mL = 12.5 mg × (5 mL ÷ 12.5 mg) = 5 mL

Answer: 5 mL

Scenario 5: Liquid concentration in mg/5 mL (ordered mg, non-integer volume)

Provider order: Acetaminophen 300 mg PO.

Label (described): Oral suspension reads “Acetaminophen 160 mg per 5 mL. Shake well. Total volume 120 mL.”

Calculate: How many mL will you administer?

Work:

mL = 300 mg × (5 mL ÷ 160 mg) = 9.375 mL

Rounded measurable volume (oral syringe): 9.4 mL

Answer: 9.4 mL

Scenario 6: Ordered mL with mg/5 mL concentration (calculate mg delivered)

Provider order: Give 15 mL of magnesium hydroxide PO PRN constipation.

Label (described): “Magnesium hydroxide 400 mg/5 mL. Directions: Take 15–30 mL once daily as needed.”

Calculate: How many mg will the patient receive with 15 mL?

Work:

mg = 15 mL × (400 mg ÷ 5 mL) = 15 × 80 mg = 1200 mg

Answer: 1200 mg

Scenario 7: Reconstitution note and “shake well”

Provider order: Amoxicillin 500 mg PO every 12 hours.

Label (described): “Amoxicillin for oral suspension. After reconstitution: 250 mg/5 mL. Shake well. Total volume after mixing: 100 mL. Refrigerate.”

Calculate: How many mL per dose?

Work:

mL = 500 mg × (5 mL ÷ 250 mg) = 10 mL

Answer: 10 mL

Scenario 8: Double-check for unusually high single dose (math + safety pause)

Provider order: Ibuprofen 800 mg PO now.

Label (described): “Ibuprofen tablets 200 mg per tablet.”

Calculate: How many tablets?

Work:

Tablets = 800 mg ÷ (200 mg/tablet) = 4 tablets

Answer: 4 tablets

Re-check prompt: Before giving, verify this is intended as a single adult dose and not a total daily limit issue per your facility’s references and patient-specific factors.

Scenario 9: Device selection and documentation

Provider order: Oxycodone oral solution 2.5 mg PO.

Label (described): “Oxycodone oral solution 1 mg/mL. Total volume 100 mL.”

Calculate: How many mL? What device is best? How would you document?

Work:

mL = 2.5 mg ÷ (1 mg/mL) = 2.5 mL

Answer (volume): 2.5 mL

Best device: Oral syringe

Example documentation: Administered oxycodone 2.5 mg (2.5 mL) PO using oral syringe.