Percentage solutions — drug calculations
Percentage solutions calculator:
work out the amount in a percentage solution
Glucose, sodium chloride and many other solutions are labelled as percentages, and working with them is a core part of drug calculations. Here you get the formula, a clear explanation and a calculator that works out how many grams a percentage solution contains, whether you are practising or just need to check a calculation quickly.
The percentage solution formula
Percentage is the number of grams per 100 ml of solution. Everything else follows from that.
Amount = (5 × 500) ÷ 100 = 25 g of glucose
Concentration: 5 × 10 = 50 mg/ml
Percentage solutions calculator
Fill in the strength and volume to see how many grams the solution contains, and its concentration in mg/ml.
Percentage solutions
The calculator is a study tool for practising drug calculations and should not be used as the basis for clinical dosing.
How percentage, grams and mg/ml fit together
Three ways of writing the same thing, and you can always convert between them.
Percentage = grams per 100 ml
A 5% solution contains 5 g of the substance in every 100 ml. That is the definition, and it is the starting point for every calculation.
Percentage × 10 = mg/ml
Because 1 g is 1000 mg and percentage refers to 100 ml, 1% is always 1000 mg ÷ 100 ml = 10 mg/ml. So 5% is 50 mg/ml, which you can then use directly in a dosage calculation.
Use mg/ml in a dosage calculation →
Does the solution need diluting? Work out the dilution →
See all the drug calculation formulas →
Frequently asked questions about percentage solutions
How do you work out how many grams are in a percentage solution?+
Use the formula Amount (g) = (Percentage × Volume in ml) ÷ 100. For example, 500 ml of 5% glucose solution contains (5 × 500) ÷ 100 = 25 g of glucose.
What does percentage mean in a drug solution?+
Percentage (%) is the number of grams of the substance per 100 ml of solution. A 5% solution therefore contains 5 g per 100 ml.
How do you convert a percentage to mg/ml?+
Multiply the percentage by 10. Because 1% means 1 g per 100 ml, which is 10 mg/ml, a 5% solution is 50 mg/ml.
Why are percentage solutions part of drug calculations?+
Many solutions, such as glucose and sodium chloride, are labelled as percentages. To work out the right dose you need to be able to convert a percentage to grams or mg/ml, and this is a standard topic in drug calculations.
Practise percentage solutions in Dos
Dos is a practice app for drug calculations, with practice tests of ten questions on percentages and concentration, a built-in calculator next to each question and statistics per topic.
