The tablet and capsule dose calculator works out exactly how many solid oral tablets or capsules to give a patient when the ordered dose and available tablet strength differ. This is the most common type of nursing drug calculation — for example, when 500mg paracetamol is ordered but only 250mg tablets are available. The formula is simply Desired ÷ Have, applied to the tablet strength rather than a liquid concentration.
Common ordered-dose and tablet-strength combinations, worked through with the Desired ÷ Have method. Results below 1 require a scored, splittable tablet.
| Ordered dose | Tablet strength | Calculation | Give |
|---|---|---|---|
| 500 mg | 250 mg | 500 ÷ 250 | 2 tablets |
| 1,000 mg | 500 mg | 1,000 ÷ 500 | 2 tablets |
| 750 mg | 250 mg | 750 ÷ 250 | 3 tablets |
| 100 mg | 50 mg | 100 ÷ 50 | 2 tablets |
| 20 mg | 10 mg | 20 ÷ 10 | 2 tablets |
| 5 mg | 2.5 mg | 5 ÷ 2.5 | 2 tablets |
| 0.5 mg | 0.25 mg | 0.5 ÷ 0.25 | 2 tablets |
| 250 mg | 500 mg | 250 ÷ 500 | ½ tablet (scored) |
| 125 mg | 250 mg | 125 ÷ 250 | ½ tablet (scored) |
If the result is more than 3 tablets for a single dose, double-check the order with the prescriber — it may indicate a transcription error or an unusual dose.
Capsules must never be split or crushed unless specifically formulated as sprinkle capsules. Scored tablets may only be halved if they have a visible score line.
If the calculated result exceeds 3 tablets for a single dose, this is a red flag. Verify the order with the prescriber before administering — it may indicate a prescribing error, an unusual dose, or a mismatch between available and required strength.
Only tablets with a visible score line are safe to split. Enteric-coated, modified-release, and film-coated tablets must never be split or crushed, as this destroys the release mechanism and can cause toxicity or ineffectiveness.
Two tablets. Using Desired ÷ Have: 500 mg ÷ 250 mg = 2 tablets. Always confirm the tablet strength on the label matches the strength you used in the calculation.
Tablets to give = Desired dose ÷ Available strength (the D/H method). For example, an order for 1,000 mg with 500 mg tablets on hand is 1,000 ÷ 500 = 2 tablets. Both values must be in the same unit before dividing.