Percent strength and ratio strength explained
Percent weight-in-volume (% w/v) means grams per 100 mL. Ratio strength 1:x means 1 g in x mL.
Method
- % w/v → grams = (percent ÷ 100) × volume in mL.
- 1:x (w/v) → mg/mL = 1000 ÷ x.
Worked examples
Example 1
How many grams of dextrose are in 500 mL of a 5% w/v solution? Round to 3 decimal places.
Show solution
- % w/v means grams per 100 mL
- 5% = 5 g / 100 mL
- 5 g/100 mL × 500 mL = 25 g
Answer: 25 g
Example 2
How many mg of drug are in 50 mL of a solution labeled 1:200 (w/v)? Round to 2 decimal places.
Show solution
- 1:200 w/v means 1 g in 200 mL, so 1,000 mg / 200 mL = 5 mg/mL
- 5 mg/mL × 50 mL = 250 mg
Answer: 250 mg
Example 3
How many grams of calcium chloride are in 10 mL of a 10% w/v solution? Round to 3 decimal places.
Show solution
- % w/v means grams per 100 mL
- 10% = 10 g / 100 mL
- 10 g/100 mL × 10 mL = 1 g
Answer: 1 g
Tips
- 0.9% sodium chloride contains 0.9 g per 100 mL.
- 1:1000 equals 1 mg/mL.
Practise with unlimited problems like these
Every problem comes with a worked solution. Free to start, no account needed.
Start practicing freePrefer paper? Our Pharmacy Technician Math Workbook has 1,000 practice calculations with step-by-step solutions, for pharmacy technician students. Also on Kindle.