How do you calculate how many tablets to give?
Divide the dose by what one tablet contains.
Tablets = Dose (mg) ÷ Strength of one tablet (mg)
For a weight-based order, work out the dose first: Dose (mg) = mg/kg × weight (kg). The rest is the same. This is the D/H formula with a volume of one tablet; the guide to dosage calculation methods shows it alongside ratio and proportion.
How to use the tablet dose calculator
- Under The dose is, choose A fixed dose in mg or Weight-based (mg/kg).
- For a fixed dose, enter the Prescribed dose in mg. For a weight-based dose, enter the Ordered dose in mg/kg and the Weight in kg.
- Enter the Tablet strength in mg per tablet, as printed on the pack.
- Read the Tablets per dose and any warning below it.
Worked examples
Example 1 – whole tablets. The order is 750 mg and the tablets are 250 mg. 750 ÷ 250 = 3 tablets.
Example 2 – half a tablet. The order is 12.5 mg and the tablets are 25 mg. 12.5 ÷ 25 = 0.5 tablets, which is half a tablet. You can only give it if the tablet is scored and may be split.
Example 3 – weight-based, not a clean result. The order is 10 mg/kg for a 32 kg patient and the tablets are 200 mg. Dose: 10 × 32 = 320 mg. Tablets: 320 ÷ 200 = 1.6 tablets. The calculator flags that this is not a whole or half tablet.
Quick reference
Tablets per dose for three common strengths.
| Dose | 125 mg tablets | 250 mg tablets | 500 mg tablets |
|---|---|---|---|
| 125 mg | 1 | 0.5 | 0.25 |
| 250 mg | 2 | 1 | 0.5 |
| 500 mg | 4 | 2 | 1 |
| 750 mg | 6 | 3 | 1.5 |
| 1,000 mg | 8 | 4 | 2 |
A result of 0.25 triggers the part-tablet warning; 6 or 8 triggers the more-than-4-tablets warning.
Common mistakes
- Mixing mg and mcg. A 50 mcg tablet is 0.05 mg. Entering 50 as mg makes the result a thousand times too small. The medication unit conversions guide covers the common slips.
- Several strengths on the shelf. The same medicine often comes in two or three strengths. The strength you enter must match the pack in your hand.
- Splitting tablets that should not be split. Unscored, modified-release or enteric-coated tablets may break unevenly, release the drug too fast or lose their protective coating.
- Combining strengths without noticing. You can make up a dose from two strengths, but count each one separately.
- Doing the weight step twice. In weight-based mode the calculator already multiplies mg/kg by the weight. It’s best not to enter a dose you have already multiplied.
A quick sense check
Most oral doses are one or two tablets. If the answer is a large number, a small fraction or an odd decimal, it’s worth rechecking the order, the unit and the strength. If no tablet strength gives a sensible count, a liquid may suit better: the mg/kg dose calculator and the mg to mL calculator work out the volume.
Frequently asked questions
How do you calculate how many tablets to give?
Divide the dose you need by the strength of one tablet. For a 750 mg dose with 250 mg tablets, 750 ÷ 250 = 3 tablets. Both numbers must be in the same unit, so convert mcg or g to mg first. The calculator shows the division and flags results that are hard to give.
Can the calculator handle weight-based doses?
Yes. Under The dose is, choose Weight-based (mg/kg), then enter the ordered dose in mg/kg and the weight in kg. The calculator first multiplies them to get the dose in mg, then divides by the tablet strength. It’s best not to enter a dose you have already multiplied by the weight.
What if the answer is not a whole number?
The calculator shows a warning whenever the result is neither a whole nor a half tablet. A result such as 1.6 tablets cannot be given accurately. It’s worth checking the order, looking for another strength of the same medicine, or asking whether a liquid form would give a measurable dose.
Can every tablet be split in half?
No. Only tablets that are scored, and whose product information allows it, are generally meant to be split. Modified-release and enteric-coated tablets are usually not meant to be split or crushed, because that can change how fast the drug is released. When in doubt, we recommend asking the pharmacist before splitting.
Why does it warn about more than 4 tablets?
Because more than four tablets for one dose is unusual and often points to a unit slip, such as mg read as mcg, or to the wrong tablet strength. The warning is a prompt to double-check, not an error in itself. Some regimens do use several tablets, so it’s worth confirming against the prescription.
My tablets are in micrograms. What do I do?
Use the same unit for the dose and the strength. Convert micrograms to mg by dividing by 1000, so 50 mcg = 0.05 mg, before entering both values. If the order and the tablet are both in mcg, the division gives the right count even without converting, but the calculator labels the fields in mg.