How to Write Measurements Correctly?

Are you writing an essay, white paper, or any other piece of technical writing? Do you have to include measurements of any kind? It might seem like writing measurements is entirely straightforward at first, but you would be surprised. This guide will delve into the conventions you need to be aware of to write measurements correctly.

Writing Measurements: The Basics

Measurements are units used to determine the length, width, weight, capacity, area, or size of an object, geographical area, or person. This process uses tools such as measuring tapes, rulers, and scales.

Although other systems do exist, the two most commonly used measuring systems are the metric and imperial systems.

The imperial system, which originated in Ancient Rome by way of Ancient Egypt, has a long history — but has largely fallen out of use outside of the United States, with some notable exceptions that include the United Kingdom, in which both systems are used.

Examples of imperial measuring units you will have encountered frequently in your daily life include:

  • Inches
  • Feet
  • Yards
  • Miles
  • Pounds
  • Ounces
  • Gallons

The metric system has a wide reach, and is used in almost the entire world. If you are engaging in informative or technical writing, readers may find it helpful if you convert any imperial measurements you include into the metric system, in which case you can place them in brackets.

Examples of commonly used metric units include:

  • Centimeters
  • Meters
  • Kilometers
  • Kilograms
  • Grams
  • Liters

How to Write Measurements Correctly

The Bureau International des Poids et Mesures, the global authority on conventions and technical decisions relating to units of measurement, offers very clear instructions on this topic in their publication The International System of Units, 9th edition.

It clarifies that:

“Unit symbols are printed in upright type regardless of the type used in the surrounding text.
They are printed in lower-case letters unless they are derived from a proper name, in which
case the first letter is a capital letter.”

That means that writers should write abbreviated unit names without capitalizing them, unless they appear at the beginning of a sentence or in a headline or title, and that unit names should not be italicized. For instance:

  • “The length of the blade is 9 inches” — not 9 Inches or 9 inches.
  • “People are being warned to keep a distance of at least 2 feet.”
  • “Gallons of milk were spilled in the grocery store today,” however. A capital is used to signify the start of a sentence.

What about situations in which you have decided to use the shorter form to denote the measurement — as in “cm”, “in”, or “kg”? We have all come to see these as abbreviations, but the Bureau International des Poids et Mesures is very clear that they’re not; these are considered “unit symbols” and “mathematical entities” instead.

Therefore, they are not capitalized, and not followed by a period. It is not considered correct to write them immediately following the relevant numbers, either — you have to leave a space. Let’s take a look at some relevant correct and incorrect examples:

  • It would be correct to write “66 m2” to denote 66 square meters, but removing the space would render the writing incorrect.
  • Write “25 g of protein per serving”, and not “25g”.
  • Write “15 lb” and not “15 lb.” or “15 lbs”.

There are some notable exceptions:

  • The unit symbol for liters may be capitalized or placed in lower case, as in “L” or “l”. Both are correct.
  • When referring to inches, a period is added — as in “6 in.”. This is done to prevent the unit symbol from being confused with the preposition “in”.
  • You may also use foot and inch marks. These are straight quotes, and not quote marks. “I am 5' 3". To achieve this effect in Microsoft Word, simply type quote marks and then use the “undo” command.

Do not abbreviate metric and imperial units by saying “80 sq. ft.” or similar ways — simply use the unit symbols, or write the entire unit name out.

When it comes to temperature, the unit names Celsius and Fahrenheit are capitalized. This is because they were named after the scientists who defined the scales, and are therefore proper nouns. You therefore refer to “220 degrees Fahrenheit” or “33 degrees Celsius”. If you wish to abbreviate, you do so by using the proper symbol, not followed by a space:

  • 220 °F
  • 33 °C

Writing Measurements: What About Decimal Points?

A period is used to indicate a decimal point in the United States, as in 2,500.25 — but in many other countries, including European countries, the convention is to use commas instead, as in 2.500,25. You will note that the period and comma have switched places in this case.

How to Write Measurements: Additional Tips

Numerous more units of measurement exist; we cannot cover them all. Examples range from familiar ones like hours, amperes, and calories to units of measurement that most people do not use in their daily lives, like microns (μ) and ohms (Ω).

When in doubt, consult the Bureau International des Poids et Mesures’ International System of Units document. This documents is freely available on the internet — and linked above for your convenience.

Likewise, depending on your goal in writing measurements, you may need to consult the relevant style guide to discover whether it is preferable to write out unit names or to choose unit symbols instead. For general use, however, this is not important. If you are writing a blog post, high school essay, or listing your home for sale on a real estate website, you get to pick between unit names and symbols yourself.


Does it matter whether I write unit names or unit symbols?

Outside of mathematical equations, both are equally practical and correct. You may choose unit names if you are writing for the general public and want to ensure that everyone understands what you are talking about, and unit names in technical writing — as it can help you be more succinct.

I constantly see people write “6g” and “8ft” — are you sure that I need to add a space?

The internet is quickly changing conventions — which can be defined as common practice embraced by the majority of people. However, you wanted to know how to write measurements correctly, and adding a space is still considered the correct choice.

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