Oral Tablets & Liquids Calculations

Calculating oral medications is a routine part of nursing practice and requires accuracy to ensure safe dosing. Whether administering tablets or oral liquids, the process involves interpreting the medication order, identifying the available stock, and applying a consistent calculation method. The same underlying principle is used in both cases, with a small adjustment depending on whether the medication is a tablet or a liquid.

What You Need to Know

Oral medication calculations are used to determine how many tablets to give or how many millilitres to administer. This depends on comparing the prescribed dose with the available stock strength.

Key points:

• medications may be supplied as tablets (e.g. mg per tablet) or liquids (e.g. mg in a set volume such as 5 mL)

• the prescribed dose and the available stock are often different

• a calculation is required to determine the correct amount to administer

• the final answer must match the form of the medication

A simple check:

• tablets → answer in number of tablets

• liquids → answer in mL

The Formula

For tablets:
Tablets = Stock Required ÷ Stock Strength

For oral liquids:
mL = (Stock Required ÷ Stock Strength) × Volume

💡How to remember: Sun Rise over Sun Set → (Stock Required divided by Stock Strength)

Where:

• Required = prescribed dose

• Stock = dose available

• Volume = the amount the stock is contained in (only used for liquids, e.g. 5 mL)

Worked Examples

Example 1: Tablets
Order: 500 mg
Stock: 250 mg per tablet

Tablets = 500 ÷ 250 = 2

Answer: 2 tablets

Example 2: Oral liquid
Order: 250 mg
Stock: 125 mg in 5 mL

mL = (250 ÷ 125) × 5
mL = 2 × 5
mL = 10

Answer: 10 mL

Example 3: Tablets (non-whole number)
Order: 75 mg
Stock: 50 mg per tablet

Tablets = 75 ÷ 50 = 1.5

Answer: 1.5 tablets

Practice Questions

1. Order: 1000 mg
   Stock: 500 mg per tablet

2. Order: 150 mg
   Stock: 75 mg per tablet

3. Order: 200 mg
   Stock: 100 mg in 5 mL

4. Order: 120 mg
   Stock: 60 mg in 5 mL

5. Order: 90 mg
   Stock: 30 mg per tablet

   (scroll down for answers)

Answers

1. 1000 ÷ 500 = 2 tablets

2. 150 ÷ 75 = 2 tablets

3. (200 ÷ 100) × 5 = 10 mL

4. (120 ÷ 60) × 5 = 10 mL

5. 90 ÷ 30 = 3 tablets