Understanding and Using Decimals In Pharmacy Calculations

This page discusses Decimals in Pharmacy Calculations.

Pharmacy Technicians perform calculations throughout their pharmacy career.

It is important to understand proper decimal usage and for you to feel comfortable and confident in decimal usage.

Dosage calculations and conversions play an integral part in the daily functions and responsibilities of the technician.

Incorrect calculation can lead to clinical errors yielding devastating consequences including death. At all costs, inadvertent dosage miscalculations need to be avoided and prevented.

The discussion of decimal error is clearly documented in most pharmaceutical calculation manuals.

Here are some suggestions which will aid the technician.

When converting from smaller units to larger units, for example from milliliters (ml) to Liters (L), the decimal place shifts to the left. In this case, 3 places to the left:

673.0 ml = 0.673 L

When converting from larger units to smaller units, example from Grams (gm) to milligrams (mg) or from milligrams (mg) to microgram’s (mcg), the decimal place shift to the right. In these cases, 3 places to the right:

1.250 gm = 1,250 mg


.15 mg = 150 mcg

Use “placeholder” zeroes which doing addition or subtraction calculations:

Example: 37.5g - .62g


- .62


Make sure that when performing calculations, they are done between units of the same measure. That is, milligrams with milligrams or Liter with Liters.

Always perform the basic conversion processes prior to performing your calculation.

e.g. 150gm added to 250KG of product yields a total volume of:

(250KG x 1000gm/KG) = (250,000 gm + 150gm) = 250,150 gm of product or 250.15 KG or product.

Keeping your calculations as simple as possible is usually the best option. It is never inappropriate to ask that your calculations be confirmed and verified. In fact, verification of ones calculations is a Best Practice!

Good Luck!

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