Units and Spacing Rules

Should There Be a Space Between Numbers and Units? A Guide to Proper Formatting

 

Units and Spacing Rules (SI and Common Units)

In the International System of Units (SI) and other standard conventions, the general rule is:

• Always include a space between the number and the unit symbol.

 

Units That Require a Space

SI Units (Standard Units)

Measurement Type	✔ Correct Example	❌ Incorrect Example
Mass	5 kg	5kg
Length	10 m	10m
Time	3 s	3s
Electric Current	12 A	12A
Temperature	25 °C	25°C
Volume	4 L or 4 l	4L
Energy	100 J	100J
Force	20 N	20N

Non-SI Units

Measurement Type	✔ Correct Example	❌ Incorrect Example
Speed	60 mph	60mph
Pressure	101 psi	101psi
Data Storage	500 MB	500MB
Frequency	50 Hz	50Hz
Power	200 W	200W

 

Exceptions: Units Without Space

1. Degree, Minute, and Second for Angles
   • ✔ Correct: 30° (degrees), 15′ (minutes), 45″ (seconds)
   • ❌ Incorrect: 30 °, 15 ′, 45 ″
2. Percentage and Permille Symbols
   • ✔ Correct: 50%, 0.1‰
   • ❌ Incorrect: 50 %, 0.1 ‰
3. Currency Symbols (When Placed Before the Number)
   • ✔ Correct: $5, €10, £20
   • ❌ Incorrect: $ 5, € 10, £ 20
   • BUT: When the symbol comes after the number, there’s a space: 5 USD, 10 EUR
4. Inch and Foot Symbols (for Measurements)
   • ✔ Correct: 5′10″
   • ❌ Incorrect: 5 ′ 10 ″

 

General Rules for Proper Spacing

1. 🟢 Always use a space between a number and its SI unit (kg, m, s, N, etc.).

2. 🛇 No space for symbols like ° (degree), % (percent), currency when placed before numbers.

 

Be consistent with formatting throughout your text or document