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.
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To work out how many tablets to give, divide the ordered dose by the strength of one tablet (Desired ÷ Have). For example, an order for 500 mg with 250 mg tablets on hand is 500 ÷ 250 = 2 tablets. Put both doses in the same unit first, and only split a tablet if it is scored.
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.
The order and the tablet strength are often written in different units, usually milligrams and micrograms. Convert one of them before you divide. Moving from a larger unit to a smaller one avoids decimals: 1 mg = 1,000 mcg and 1 g = 1,000 mg.
| Ordered | Tablets on hand | Convert first | Then divide | Give |
|---|---|---|---|---|
| 0.125 mg | 62.5 mcg | 0.125 mg = 125 mcg | 125 ÷ 62.5 | 2 tablets |
| 1 g | 500 mg | 1 g = 1,000 mg | 1,000 ÷ 500 | 2 tablets |
| 0.1 mg | 50 mcg | 0.1 mg = 100 mcg | 100 ÷ 50 | 2 tablets |
| 0.5 mg | 250 mcg | 0.5 mg = 500 mcg | 500 ÷ 250 | 2 tablets |
Dividing without converting gives answers like 0.002 tablets or 500 tablets, which no one would give. That is the point of the reasonableness check: a single dose is almost always between half a tablet and three tablets. Anything outside that range means a unit is wrong, the stock strength is wrong, or the order needs clarifying.
The calculator above converts between g, mg and mcg for you and shows the converted dose next to the answer. It will not convert mEq or units, which have to be entered in the same unit on both sides.
Halving is only an option for tablets with a score line, and only if the product information allows it. Modified-release, extended-release and enteric-coated tablets, and most capsules, must not be split, crushed or opened. Breaking the coating can release the whole dose at once or let stomach acid destroy the drug. The Institute for Safe Medication Practices keeps a list of oral dosage forms that should not be crushed, and most hospital pharmacies publish their own.
If a patient cannot swallow tablets, the answer is rarely to crush whatever is in the drawer. Ask the pharmacist about a liquid or dispersible form. The dose then becomes a volume calculation; the liquid dose calculator works that through.
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.
Convert first, then divide. 1 mg = 1,000 mcg, so an order for 0.125 mg is 125 mcg. With 62.5 mcg tablets, 125 ÷ 62.5 = 2 tablets. Converting to the smaller unit avoids working with decimals.