Grammar and Style/Numbers and Units/Numbers and Units
As a science communicator, you will often have to include highly specific information in your written materials. For example, you might be writing a lab report in which you provide numerical details about the method you used in your experiment. Within STEM fields, there are some common practices that will allow you to effectively convey your message, especially when working with numbers.
Some Basic Practices Related to Writing About Numbers
| Practice | Example |
|---|---|
| Spell out small numbers (one to nine). | I performed three experiments yesterday. |
| Use numerals for larger numbers (10 +),except when beginning a sentence. | Mike performed 12 experiments.
Fifteen days later, he collected the data. |
| Use numerals for counts, percentages, decimals, magnifications, and official scales. | We found 8 mice, 12 rats, and 37 rabbits. Mammal populations here have grown by about 30 % in the last five years. |
| Use spaces to make numbers with many digits easier to interpret (do not use commas as they represent the decimal marker in many European and other countries). One space separates three figures, both before and after the decimal, though a four-digit number should not be written with a space. | There are 5194 new species of insect discovered each year. Before rounding, our experimental value was determined to be 98 765.4321 µF. The Boltzmann Constant is defined to be 1.380 649 × 10-23 J/K.
There are approximately 7.5 million insect species on Earth. |
| Avoid having two distinct numbers written next to one another, most simply by rearranging a sentence. | We tested 15 different 19-year-olds not ‘we tested 15 19-year-olds.‘ |
| Spell out names and nouns. | The First Law of Thermodynamics. |
| Use numerals for dates. For short date format, YYYY-MM-DD is advised. | On March 4, we have an exam. Examination date: 2020-03-04. |
| Use numerals for times,
except when writing ‘o’clock’ or ‘hours’ |
The exam begins at 9:30 (09:30),
and finishes at one o’clock (thirteen hours). |
| Use numerals for currency references. | My lunch cost $4.35, but the chips were only 85 cents. |
Always remember to be consistent in your style. If two guidelines clash in one sentence, you will have to favour one over the other. Make sure you continue to favour that one over the other throughout your text.
Some Basic Practices Related to Writing About Units
It is common in STEM fields to abbreviate units of scientific measurement. When writing, it is important to use the correct abbreviations. At best, erroneous abbreviations give the impression that you don’t care about your work, but they also have the potential to confuse your readers.
The table below shows the correct symbols for many commonly used scientific measurements, as well as some of the most important guidelines governing their use in STEM writing.
| Scientific Measurement | Symbol |
|---|---|
| Practices for Appropriate Use | Example |
| Do not pluralize unit abbreviations. | |
| Only use a period after abbreviations if they end a sentence. | |
| Put a space between numerals and unit abbreviations, unless using angular degrees, arcminutes, or arcseconds. The space practice also applies to degrees Celsius and percentages. | |
| Do not capitalize unit symbols unless they are named after people (e.g. kelvin, joule).
Litres have been granted an exception to this practice due to 'l' appearing similar to the number '1' and so can be written as either 'l' or 'L.' Millilitres (and other multiples) should still be written as 'ml.' |