How To Write Out Measurements: The Complete Guide To Academic, Technical, And Professional Styles

Writing out measurements accurately requires aligning your text with a specific style guide: technical and academic styles (such as APA and IEEE) mandate numerals alongside abbreviated units, whereas editorial styles (like Chicago) favor spelling out both the number and the unit in non-technical contexts. To ensure absolute professional consistency, always maintain a single space between the quantity and the unit, use hyphens for compound modifiers preceding nouns, and never mix symbols with spelled-out numbers.

Pre-Writing Alignment & Style Selection

Before writing any measurement, you must establish which style guide governs your document. Mixing rules from different manuals creates an inconsistent, unprofessional manuscript that can lead to misinterpretation, peer-review rejection, or technical errors in manufacturing and engineering.

Essential Reference Tools and Standards

• Primary Style Manuals: Keep copy-specific resources accessible, such as the Chicago Manual of Style (CMOS 17th Edition) for general publishing, the Associated Press (AP) Stylebook for journalism, the American Psychological Association (APA 7th Edition) for behavioral sciences, or the IEEE Editorial Style Manual for technical and engineering disciplines.
• International Standards Reference: Access the BIPM (Bureau International des Poids et Mesures) SI Brochure to reference globally accepted rules for metric units.
• Target Audience Scope: Identify if your readers are general consumers (requiring spelled-out US Customary units like "pounds" or "inches") or technical specialists (requiring precise, abbreviated SI metric notations like "kg" or "mm").
• Style Setup Parameters: Expect to invest approximately 10 to 15 minutes establishing a project-wide localized stylesheet to document exceptions, preferred spelling of units, and chosen measurement standards.

Mastering the Core Rules of Measurement Notation

To write measurements with consistent technical accuracy, follow these structural steps.

Step 1: Choose Between Numerals and Spelled-Out Words

The decision to write a number as a numeral (e.g., 5) or a word (e.g., five) depends entirely on your industry style guide and whether your document is technical or literary.

1. Technical, Scientific, and Academic Style (APA, IEEE, SI): Always use figures/numerals before any unit of measurement, regardless of how small the number is.
   
   
   • Correct: The specimen weighed 3 g.
   • Correct: The reaction completed in 8 hours.
2. General Editorial and Literary Style (Chicago Manual of Style): In non-technical manuscripts, spell out isolated, whole-number measurements under 10.
   
   
   • Correct: The bookshelf was only three inches wide.
   • Correct: We hiked six miles before setting up camp.
3. Journalistic Style (AP Style): Always use figures for dimensions, distances, speeds, and temperatures, even if the number is less than 10.
   
   
   • Correct: The wind was blowing at 8 mph.
   • Correct: The child is 4 feet tall.

Warning: Never begin a sentence with a numeral, even if the measurement rules dictate using figures. If a measurement must start a sentence, spell out both the number and the unit, or rewrite the sentence to place the measurement elsewhere.

• Incorrect: 15 cm of snow fell overnight.
• Correct: Fifteen centimeters of snow fell overnight.
• Better: Overnight, 15 cm of snow fell.

Step 2: Format Abbreviations and Unit Symbols Correctly

Unit symbols are mathematical entities, not abbreviations. They must follow precise typographical standards to maintain clear communication.

1. The Spacing Rule: Insert a single, non-breaking space between the numerical value and the unit symbol. This prevents the number and unit from splitting across line breaks.
   
   
   • Correct: 12 mm | 50 kg | 300 K
   • Incorrect: 12mm | 50kg | 300K
   • Exceptions: Do not place a space before the degree symbol for angles (e.g., a 90° angle) or before the percent sign in general writing (e.g., 15%).
2. Avoid Punctuation in Symbols: Do not place a period after an SI unit symbol, unless it occurs at the very end of a sentence.
   
   
   • Correct: The wire length was 4 m, which was ideal.
   • Incorrect: The wire length was 4 m., which was ideal.
   • Exception for US Customary Units: In AP and Chicago styles, the abbreviation for "inch" (in.) takes a period to prevent confusion with the preposition "in".
3. Prevent Pluralization Errors: Never add an "s" to make a unit symbol plural. The symbol remains singular regardless of the quantity.
   
   
   • Correct: 45 kg
   • Incorrect: 45 kgs

Step 3: Apply Hyphenation to Compound Modifiers

When a measurement is used as a compound adjective directly preceding a noun, the formatting changes depending on whether you are using abbreviations or spelled-out words.

1. When Spelled Out: Use a hyphen to connect the number and the unit when they function as a unit modifier before a noun.
   
   
   • Correct: A twenty-foot pole.
   • Correct: A three-hour delay.
2. When Using Numerals with Spelled-Out Units: Use a hyphen to connect the numeral to the unit.
   
   
   • Correct: A 10-foot pole.
   • Correct: A 5-liter container.
3. When Using Unit Symbols (SI and IEEE rules): Do not use a hyphen between a numeral and an abbreviated unit symbol, even when it acts as an adjective. The space alone is sufficient.
   
   
   • Correct: A 10 mm gap.
   • Incorrect: A 10-mm gap.
   • Note: While SI/IEEE discourages the hyphen in this scenario to protect symbol integrity, Chicago and APA style guides still prefer the hyphen (e.g., a 10-mm gap). Check your publication specifications.

Step 4: Handle Ranges, Tolerances, and Units of Area

When presenting multiple measurements or complex mathematical ranges, write the unit in a way that eliminates any possibility of user or reader error.

1. Expressing Ranges: In technical writing, repeat the unit symbol or percentage sign for every value in a range to avoid ambiguity.
   
   
   • Correct: The temperature fluctuated between 15 °C and 25 °C.
   • Correct: The mixture contained 10% to 15% active catalyst.
   • Incorrect: The temperature fluctuated between 15 and 25 °C.
2. Area and Volume Dimensions: Repeat the unit for each dimension when writing length, width, and height.
   
   
   • Correct: The room measures 3 m × 4 m.
   • Acceptable: The box was 12 in. by 18 in. by 24 in.
   • Incorrect: The room measures 3 × 4 m.

Pro-Tip: When using a range dash (en dash "–") in academic or engineering publications, do not mix it with the words "from" or "between". Use "from 10 to 20 mm" or "10–20 mm," but never "between 10–20 mm."

Comprehensive Style Guide Comparison & Unit Notation Specs

The following table contrasts formatting standards across major publishing and technical style manuals, using metric and US customary examples.

Common Notation Errors & Editorial Remedies

Failure 1: The "Dangling Unit" in Dimension Calculations

• Root Cause: Writing dimensions as a single block of numbers with a single unit symbol at the end (e.g., "10 × 15 × 20 mm"). This causes ambiguity because it is unclear if the first two dimensions are also in millimeters or another unit.
• Actionable Fix: Explicitly state the unit for every single dimension. Change "10 × 15 × 20 mm" to "10 mm × 15 mm × 20 mm" or write it out as "10 by 15 by 20 millimeters" in non-technical manuscripts.

Failure 2: Unit-Symbol Pluralization Errors

• Root Cause: Treating standard metric unit symbols as standard words and adding an "s" to show plurality (e.g., "50 kgs" or "12 cms").
• Actionable Fix: Ensure all metric unit symbols remain in their singular form. Correct "50 kgs" to "50 kg" and "12 cms" to "12 cm". Keep units plural only when writing out the full name of the unit (e.g., "50 kilograms").

Failure 3: Combining Numerals with Spelled-Out Units in Hyphenated Phrases

• Root Cause: Creating hybrid modifiers that combine a spelled-out number with an abbreviated symbol, or a numeral with an unspaced symbol, like "a 5-in pipe" or "a 12-mm-thick sheet".
• Actionable Fix: Match the terminology. If using the symbol, keep it separate and unhyphenated in scientific styles ("a 12 mm thick sheet") or spell it out fully when hyphenated in general styles ("a five-inch pipe" or "a 12-millimeter-thick sheet").

Failure 4: The Closed-Up Value and Unit

• Root Cause: Omitting the space between the number and the unit (e.g., "100m", "35°C", "12g"). This makes the text dense and violates SI standards.
• Actionable Fix: Insert a single non-breaking space (Ctrl+Shift+Space in Microsoft Word or   in HTML) between the numeral and the unit. Correct "100m" to "100 m", and "12g" to "12 g".

Frequently Asked Questions

Do you put a space between the number and the unit?

Yes. Under international SI metrics, APA, and IEEE guidelines, you must always place a space between the numerical value and the unit symbol (e.g., 50 mL, not 50mL). The only major exceptions are the degree symbol for angles (e.g., 180°) and the percent symbol in non-SI styles (e.g., 99%).

Is it "percent" or the "%" symbol when writing measurements?

The choice depends on your style guide. General editorial publications (Chicago Style) and journalism (AP Style) prefer writing out "percent" in non-technical copy, though both now accept the "%" symbol to save space. Academic and scientific guides (APA and IEEE) require using the "%" symbol whenever it is paired with a numeral (e.g., 12.5%).

How do you write out dimensions like length, width, and height?

In technical publications, write dimensions by repeating the unit symbol for each measurement, separated by a multiplication sign (e.g., 5 m × 10 m × 3 m). For general audiences or literary works, write out the numbers and units fully using descriptive words (e.g., "a room measuring twelve feet by fifteen feet").

Should I use abbreviations for standard US customary units?

In general prose, write out US customary units completely (e.g., inches, feet, miles, pounds). Only use abbreviations (in., ft., mi., lb.) in technical documents, data tables, or when space is highly limited, making sure to follow your specific style manual's punctuation rules.

How do you write temperature scales like Celsius and Fahrenheit?

For technical documents using SI/IEEE guidelines, place a space between the number and the degree symbol but no space between the degree symbol and the scale letter (e.g., 37 °C). In general editorial writing, Chicago style closes all spaces entirely (e.g., 98.6°F).

Establish Your Professional Style Standards

Developing clear, accurate technical communications starts with maintaining uniform measurement standards across all internal and external documents. Implement a centralized company stylesheet today to align your engineering, product, and publishing teams under one cohesive voice.