Percentage Calculation Formula in Pharmacy

Percentage calculation is very useful in pharmacy and pharmaceutical calculations to measure the number of grams contained in 100 mL of solution. Which is expressed by Percent Weight in Volume (%w/v).

Percentage Calculation Formula

To determine the percentage of X, we have to divide the value (X) by the total value (Y) and then multiply the resultant by 100.

Percentage (%) = X/Y  ×100%

Percentage Calculation Example

1. Express 1:2000 as a percentage strength.

1 part/2000 parts = X parts/100 parts.

So, X = 1 × 100/2000 = 0.05%

2. Express 0.5% w/w as a ratio strength.

0.5 g/100 g = 1 part/X parts.

X = 100 × 1/0.5

X = 200

Therefore, the ratio strength = 1:1000

3. Express 5 ppm as a percentage strength.

5 ppm = 5 part per million = 5:1000000

So, 5 part/1000000 = X parts/100 parts

X = 5 × 100/1000000 = 0.0005%

Pharmaceutical Percentage Calculation

1. Express 1 in 200 w/v solution of potassium permanganate as a percentage.

1/200 = X / 100

X = 1 × 100/200 = 0.5% w/v

2. How many grams of a drug should be used to prepare 250 g of a 10% w/w solution?

Let X be the weight of the drug needed:

So, X/250 = 10 g/100 g

X = 10 × 250/100 = 25 g

3. Express 1.8 g of sodium chloride, made up to 200 mL with water, as a percentage.

1.8/200 = X/100

X = 100 × 1.8/200 = 0.9%