Skip to Main Content

Drug Calculations for Nursing


Drug Calculations Supporttablets

Nurses need to facilitate the safe and accurate administration of medicines.  To do this they need to carry out basic drug calculations.

These materials have been created in order to help students understand the basic maths required in order to carry out those drug calculations. The materials have been designed using one method of calculations, for alternative methods and advice please see the recommended books on this page or discuss with your tutors.

This advice is for a number of different courses. Please check with your module leader as to which guidance is most relevant to you.

Four Operations

In order to perform drug calculations, there are a number of arithmetic operations you will need to revise, these are:

  • Addition of two or more decimal numbers
  • Multiplication using the column method, chunking or repeated addition
  • Division using the 'Bus Stop' method or similar

The resources below have been created to help you to build your confidence in these.

For additional questions, you can use the following links courtesy of Corbett Maths:

Decimals: addition     Video 90     Practice Questions      Textbook Exercise

Multiplication: column method  Video 200    Practice Questions    Textbook 1    Textbook 2

Division: short division   Video 98     Practice Questions    Textbook Exercise


A very important calculations you will be required to do is to convert within the metric system, specifically between grams, milligrams and micrograms.

The content below will demonstrate the easiest way to do this:

Being able to convert quickly and without a calculator is very important when dealing with drug calculations.


One of the most important steps when calculating dosages is to simplify fractions.

Simplifying fractions makes later calculations much easier - particularly important when calculating dose by hand.

For more questions and support, why not use the following links courtesy of Corbett Maths:

Fractions: simplifying     Video 146     Practice Questions    Textbook Exercise

Tablet Calcuations

A common question in drugs calculation exams is to find the number of tablets required given a prescribed dose and a specified weight of stock tablet.

This is much more straightforward that it may seem at first and can often be calculated by simply counting tablets out until you reach the prescribed dose.

The following video talks through the two main strategies of calculating tablets:

It is important to always check that both the prescription and stock are using the same units.

There are great resources near the bottom of this page which allow you to revise these questions.


Suspensions describe liquid medication, which can be given orally or via injection, which has active medication suspended in fluid for easy delivery. Please note that there is no difference in the calculation require between liquid medication and injections.

These represent some of the harder questions, as unlike our whole or half tablets, liquid medication can be more accurately measured using a syringe, in some cases to up to two decimal places.

Different courses require different levels of difficulty, Child Nursing for example may be required to calculate non-standard doses that end in decimal places. Always check with your module leader to ensure you are practicing questions appropriate for your course.

Whilst the 'NHS' formula method is a particularly robust method, with even the most difficult questions broken into 5 clear steps, there is a quicker method that can be used - often called the ratio method. Please be aware however that, whilst this method is particularly quick for simple questions, more complex questions can be much harder to solve this way due to the 'trial and error' style approach.

Both these methods can be practiced using the resources further down the page.


Whilst injections and oral medications are often given in bolus (all in one go), some medication is given over time using an infusion pump.

Infusion calculations focus on working out how much medication needs to be given each hour to fulfil the required dose over the required time. Due to this, it is important to focus on millilitres and hours, as all infusion pumps are programmed in millilitres per hour.

Please note that from 2023, infusions are no longer on the adult nurse drug calculations exam - please check with your module tutor to check if you need to practice these questions.

Online Resources

There are a wide range of online resources available to practice these questions.

A question generator for Adult, Child, Mental Health and Learning Disability nursing has been developed to give a range of practice questions.

Please note that whilst we have made every effort to ensure these questions are representative of the exam you will experience, due to the randomisation of questions, you will encounter questions both above and below the difficulty of your actual exam.

After opening the tool on a computer, select your nursing strand, you can then randomise the questions by hitting the delete button on your keyboard. Answers can be found at the bottom of the page. This tool can also be opened on your phone, though to randomise questions, you will need to close and reopen the file.

The tool includes options to disable half tablets and conversions between g, mg and mcg to reduce the difficulty.

More online resources can be found below:

Useful web links and further reading

Click on the image to see additional useful resources

Reading list

Using Material on this page