Missing space between numeric value and unit (e.g., 25 km)

Small spacing and hyphen choices change how readers parse measurements. Below are compact rules, exceptions, and many ready-to-copy rewrites for work, school, and casual writing.

Quick answer

Put a (nonbreaking) space between a numeral and a unit symbol in most formal writing: write 5 km, 250 g, 30 °C. Hyphenate when the measurement is a compound adjective before a noun: a 5-km run. Common exceptions: percent (%) usually has no space (5%), currency symbols often attach to the number ($5), and angle/prime symbols (90°, 5') omit the space.

Formal/technical: space between number and unit (5 km).
Compound adjective before noun: hyphenate (a 5-km run).
Percent: usually no space (5%). Currency symbol before number: $5 (no space); abbreviated code after number: 5 USD (space).
Angles/primes: no space (90°, 5').

Core rule: keep number and unit separate (usually)

Most style guides and the SI system put a (nonbreaking) space between the numeral and the unit symbol: 5 km, 250 mL, 12 kg, 3 h. The space helps readers parse quantities and prevents awkward line breaks.

Form: [number][space][unit] - e.g., 50 km, 250 g, 1.5 m.
Use a nonbreaking space in documents so the number and unit stay together on the same line.

Wrong: She ran 5km today.
Right: She ran 5 km today.
Wrong: The package weighed 2kg.
Right: The package weighed 2 kg.

Spacing for common symbols: °, %, and currency

Temperature: SI recommends a space before the degree sign plus letter (30 °C). Newspapers and casual writers often drop the space (30°C) - pick a style and stay consistent.

Percent and currency follow different conventions. English usage typically writes 5% (no space). Currency symbols usually precede the number ($5, €10); when using an abbreviated currency code after the number, add a space (50 USD).

Temperature (SI): 30 °C; casual/press: 30°C.
Percent: usually 5% in English; some technical docs use 5 %.
Currency: $5 or €10 (symbol before number, no space); 50 USD (space before code).

Wrong: The temperature is 30°C.
Right: The temperature is 30 °C.
Wrong: Profit rose by 5 % last quarter.
Right: Profit rose by 5% last quarter.
Wrong: The fee is 50$.
Right: The fee is $50.

Hyphenation: when measurements become adjectives

When a measurement directly modifies a noun, hyphenate number and unit to form a compound adjective: a 5-km race, a 10-minute break, a 3-cm margin. When the measurement follows the noun or is a predicate, separate with a space: The race is 5 km long; The break lasted 10 minutes.

Before a noun (adjective): hyphenate - a 5-km run.
After a noun or as predicate: do not hyphenate - the run was 5 km.

Wrong: She finished a 5 km-run in under 30 minutes.
Right: She finished a 5-km run in under 30 minutes.
Wrong: We need a 20 person-team for this task.
Right: We need a 20-person team for this task.

Grammar notes: nonbreaking spaces, plurals, angles/primes, and time

Use a nonbreaking space to keep number + unit together (e.g., 5 km). Do not pluralize unit symbols: write 3 kg, not 3 kgs. Angle and prime symbols usually have no space: 90°, 5', 30". Time formats vary by house style - don't mix 9 a.m., 09:00, and 9AM in one document.

Nonbreaking space prevents line breaks between number and unit.
No plural s on unit symbols: 3 kg, not 3 kgs.
Angles/primes: 90°, 5', 30" (no space).

Wrong: Turn to 90 ° on the protractor.
Right: Turn to 90° on the protractor.
Wrong: I'll be there at 5pm.
Right: I'll be there at 5 a.m. (or 17:00 for 24-hour style).

Real usage: formal, school, and casual tones

Choose the level of formality to guide spacing and hyphenation. Work and scientific reports prefer SI spacing and hyphenated adjectival forms. School labs often expect spaced units and correct hyphenation. Casual messages often omit spaces to save characters, but consistency still helps readability.

Work/class: default to spaced units and hyphenate adjectival measurements.
Casual: many omit the space; focus on clarity.

Work: The blueprint specifies a corridor width of 1.2 m.
Work: Yearly revenue rose 12% compared with last year.
Work: Please attach a 6-page summary to the submission.
School: Each lap measured 25 m in the pool.
School: Record a 15-minute reaction time for each trial.
School: The slide was prepared with a 1.5 cm marker.
Casual: Ran 8km this morning - feeling great!
Casual: Bought a €5 shirt at the market.
Casual: Coffee was 80°C when I grabbed it (ouch).

Try your own sentence

Read the whole sentence for context - that usually clarifies whether to space or hyphenate. Use the widget below to check a sentence quickly.

Rewrite help: checklist and ready-to-copy fixes

Checklist: (1) Is a numeral followed by a unit symbol? Add a nonbreaking space for formal writing. (2) Does the measurement modify a noun? Hyphenate. (3) Is it an exception (%,$,°,')? Apply that symbol's convention. (4) Enforce nonbreaking spaces in long documents.

Rewrite:
Wrong: She ran 5km today. →
Right: She ran 5 km today.
Rewrite:
Wrong: The exam starts at 9am. →
Right: The exam starts at 9 a.m. (or 09:00).
Rewrite:
Wrong: We ordered a 10 pound bag of flour. →
Right: We ordered a 10-pound bag of flour.
Rewrite:
Wrong: The coffee was 90°C when I poured it. →
Right: The coffee was 90 °C when I poured it. (
Casual: 90°C is acceptable.)
Rewrite:
Wrong: Sales increased by 7 % last year. →
Right: Sales increased by 7% last year.
Rewrite:
Wrong: The sample measured 2L. →
Right: The sample measured 2 L.

Examples you can copy: grouped by work, school, and casual

Swap numbers or units in these templates while keeping spacing and hyphenation patterns.

Work: The specifications require a 2.5 m clearance under the beam.
Work: Annual growth reached 12% year over year.
Work: Please attach a 6-page summary to the submission.
School: Each lap measured 25 m in the pool.
School: Record a 15-minute reaction time for each trial.
School: Prepare slides with a 1.5 cm marker.
Casual: Just ran 10km - felt strong!
Casual: Bought a €5 shirt at the market.
Casual: Coffee was 80°C when I grabbed it (ouch).

Memory trick and quick fixes

Mnemonic: "Number + space + Unit" = measurement value; "Number-Unit-noun" = hyphenated adjective. If it modifies a noun, glue with hyphens; if it reports a measurement, separate with a space.

Editor tricks: use Find/Replace with regex or set a style rule to insert nonbreaking spaces after numerals. That fixes most instances quickly.

Separate neighbors (space) or make a single adjective (hyphen).
Use nonbreaking spaces in long documents to avoid line breaks between number and unit.
Set team style: e.g., Percent = 5%; Temperature = 30 °C (or 30°C).

Tip: Regex example (add normal space): Find '([0-9])(?:km|kg|mL|cm)\b' → Replace '\1 \2'.
Tip: Replace ordinary space with a nonbreaking space (U+00A0) between number and unit in long reports.

Similar mistakes to watch for

Unit spacing often appears alongside percent spacing, inconsistent time formatting, incorrect currency placement, unnecessary plural s on units, and misplaced hyphens in compound numbers.

Percent spacing: decide on 5% or 5 % and be consistent.
Time formats: don't mix 9 a.m., 09:00, and 9AM in one document.
Currency placement: $5 (symbol before number) vs 5 USD (space before code).
Unit plurals: use 3 kg, not 3 kgs.

Wrong: The discount is 10 % and the fee is 50$.
Right: The discount is 10% and the fee is $50.
Wrong: We need 4kgs of material.
Right: We need 4 kg of material.

FAQ

Should I write 5km or 5 km?

In formal and technical writing, write 5 km (use a nonbreaking space). In casual contexts, many write 5km. When in doubt, follow your organization's or publisher's style guide.

Do I put a space before the percent sign (%)?

Most English publications write the percent sign directly after the numeral (5%). Some technical documents use a space (5 %). Choose one convention and stay consistent.

Is it 30°C or 30 °C?

Scientific and SI-style sources prefer 30 °C. Newspapers and casual digital contexts often use 30°C. Use the spaced form for formal reports unless house style dictates otherwise.

When do I hyphenate measurements (5-km vs 5 km)?

Hyphenate when the measurement directly modifies a noun (a 5-km race). Do not hyphenate when the measurement follows the noun or stands alone (the race was 5 km).

How can I check my document quickly?

Find/Replace common unit abbreviations to add spaces, run a grammar/style checker that flags spacing and hyphenation, and create a short style note (percent, temperature, currency) to enforce across the document.

Want a quick fix for unit spacing across a document?

Create a short team style note (temperature: 30 °C or 30°C; percent: 5% or 5 %) and use Find/Replace or a grammar checker to enforce it. If unsure about a sentence, paste it into your checker and apply one of the rewrites above.