Dosage Practice

Tablet Dosage Calculation: How Many Tablets to Give

Divide the dose ordered by the strength of one tablet: desired ÷ have × 1 tablet. If the order is in grams and the tablets in milligrams, convert first so both are in the same unit.

The Formula

tablets = desired dose ÷ dose per tablet

D ÷ H × Q, where Q is one tablet.

How to work it out

  1. 1 Check the units. Order in grams, tablets in milligrams? Convert the order to milligrams first.
  2. 2 Divide the ordered dose by the strength of one tablet.
  3. 3 Answers should come out as whole tablets or halves. A quarter tablet, or 2.7 tablets, means something is wrong: recheck the conversion.
  4. 4 Capsules cannot be split. If the answer is not a whole number of capsules, the order needs to be queried.

Worked Examples

Example 1

Ordered: 750 mg by mouth. On hand: 250 mg tablets. How many tablets?

  1. Same units, so divide straight away.
  2. 750 mg ÷ 250 mg per tablet = 3 tablets.

Answer: 3 tablets

Example 2

Ordered: digoxin 0.125 mg by mouth. On hand: 0.25 mg scored tablets. How many tablets?

  1. 0.125 mg ÷ 0.25 mg per tablet = 0.5.
  2. The tablet is scored, so half a tablet can be given.

Answer: 0.5 tablet

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Problem 1 of 3No sign-up needed

Ordered: 100 mg by mouth. On hand: 50 mg tablets. How many tablets will you give?

Give the exact number of tablets

tablets

Common Mistakes

  • Skipping the gram to milligram conversion

    Ordered 0.5 g, tablets 250 mg: dividing 0.5 by 250 gives nonsense. Convert 0.5 g to 500 mg first, then divide to get 2 tablets.

  • Dividing the wrong way

    Desired goes on top. If the answer is less than one when the order is clearly bigger than one tablet's strength, the division is upside down.

  • Splitting what cannot be split

    Capsules and enteric-coated or extended-release tablets are not split. An answer of 1.5 capsules is a signal to question the order, not to give it.

Questions Students Ask

What is the formula method?

Desired over have, times quantity: the dose ordered divided by the dose on hand, multiplied by the form it comes in. For tablets the quantity is 1 tablet.

What if the answer is 2.5 tablets?

If the tablet is scored, two and a half tablets is a valid answer. If not, or if the number is odd like 2.3, recheck your units and consider that the order needs clarification.

Keep practicing in lesson 4: Tablets and Capsules

Fresh numbers every time. Ten correct answers finish the lesson. The practice round and the first five problems of lesson 1 are free.

Open lesson 4