Using numbers and handling data
Using numbers and handling data

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Using numbers and handling data

1.5 Rounding to decimal places

Sometimes the result of a calculation gives a number with lots of decimal places - far more than you need or could reliably measure. For instance, suppose a patient is required to receive 5 ml of medicine a day, evenly spaced in three injections. How much medicine should they be given in each dose?

To divide the 5 ml of medicine into three equal parts would mean measuring out 5 ÷ 3 = 1.6666 ml (where the 6s keep repeating, or recurring indefinitely). It's not realistic or feasible to measure out the medicine to this kind of accuracy. Instead, you first need to think about what level of accuracy is needed. An injection of this volume would be most accurately dispensed using a 2 ml syringe, marked in 0.1 ml increments. In this case then, the accuracy of your measurement would be limited to 0.1 ml, or in other words to one decimal place. To administer the amount calculated above you would need to round the figure to the nearest decimal place.

The rule to remember with rounding to a particular decimal place is that if the next number to the right of that decimal place is 5 or more, you round the figure up to the next highest number, and if it's 4 or less it remains the same. For instance, to correct 1.6666 ml to one decimal place, find the first decimal place and then look at the next (smaller) decimal place to its right, which we've highlighted here as 1.6666 ml. As this number is greater than 5 we have to round up, and the amount becomes 1.7 ml corrected to one decimal place (1 dp). If the original number had been 1.6466 ml then the value corrected to one decimal place would be 1.6 ml (1 dp).

Here are some more worked examples for you to practise with:

Now try rounding numbers to specific decimal places for yourself with practice question 9.

Right click and open the practice questions [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] in a separate window, then you can switch easily between the course text and the questions.

Box 1 General rules for numbers in healthcare

  • Try to avoid the need for a decimal point

    • Use 500 mg not 0.5 g

    • Use 125 mcg not 0.125 mg

  • Never leave a decimal point 'naked'

    • Paracetamol 0.5 mg not Paracetamol .5 mg

  • Avoid using a terminal zero

    • Diazepam 2 mg not Diazepam 2.0 mg

  • Put a space between the drug name and dose

    • Apresoline 55 mg not Apresoline55 mg

S110_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371