Split Numbers from Units of Measure?

Yes, you should split numbers from units of measure in most writing, meaning you put a space between the numeral and the unit (e.g., 5 kg, not 5kg). This article explains the rule, its exceptions, and how to apply it consistently in technical, scientific, and everyday writing.

Formula

The calculator above works out your average pace and speed from a finish time and distance. The formulas are:

• Pace (min/km) = Finish time (min) ÷ Distance (km)
• Speed (km/h) = Distance (km) ÷ (Finish time (min) ÷ 60)

Where t is the finish time in minutes, d is the distance in kilometres, pace is in minutes per kilometre, and speed is in kilometres per hour.

Worked Example

Using the default values: finish time = 50 minutes, distance = 10 km.

1. Pace = 50 ÷ 10 = 5.00 min/km
2. Speed = 10 ÷ (50 ÷ 60) = 10 ÷ 0.8333 = 12.00 km/h

The calculator displays 5.00 min/km as the headline answer and 12.00 km/h as the second output.

Why the Space Matters

The space between a number and a unit is not just a typographical preference; it is a rule in the International System of Units (SI). The SI Brochure, published by the International Bureau of Weights and Measures (BIPM), states that a space must separate the numerical value and the unit symbol. For example, write 25 kg, not 25kg. This rule applies to all SI units, including derived units like m/s (metres per second) and kg/m³ (kilograms per cubic metre).

The reason is clarity. Without the space, a number and a unit can be mistaken for a single word or a different unit. For instance, 10ms could be read as 10 milliseconds, but 10 ms is unambiguous. Similarly, 5kg might be parsed as a single token, while 5 kg clearly separates the quantity from the unit.

In practice, the space is a small but important part of technical writing. It prevents errors in calculations, data entry, and communication. When a document uses units consistently with spaces, it looks professional and reduces the chance of misinterpretation.

Exceptions and Special Cases

Not every situation follows the space rule. Here are the main exceptions:

• Percent and degree symbols: The percent sign (%) is written directly after the number (e.g., 50%), and the degree symbol (°) for temperature is also attached (e.g., 25°C). However, for angles, a space is used: 45° (no space) is common, but the SI recommends a space before the degree symbol for plane angles, so 45 ° is acceptable. In practice, the no-space form is more common.
• Currency symbols: Currency symbols like $, €, £ are placed before the number with no space (e.g., $25), but ISO currency codes are placed after with a space (e.g., 25 USD).
• Unit names vs. symbols: When you write the full unit name (e.g., kilograms), you still use a space: 5 kilograms. The space is always used between a number and a unit name.
• Compound units: In compound units like km/h, the space is used only between the number and the first unit, not between the units themselves. For example, 60 km/h, not 60 km / h (though a space around the slash is sometimes seen, it is not standard).
• Dimensionless quantities: When a quantity is dimensionless (like a count or a ratio), no unit is used, so the space is irrelevant. For example, 3 apples has a space, but 3 alone is fine.

How to Choose the Right Format

Choosing the right format depends on the style guide you are following. Most scientific and technical style guides, including the Chicago Manual of Style, the APA Style, and the IEEE Editorial Style Manual, recommend a space between a number and a unit. For example:

• APA: 10 cm
• Chicago: 10 cm
• IEEE: 10 cm

In contrast, some non-technical publications may omit the space for aesthetic reasons, but this is not recommended in formal writing. The key is to be consistent within a document. If you are writing for a specific journal or publisher, check their guidelines.

For web content, the space is also recommended because it improves readability and accessibility. Screen readers often read numbers and units separately when there is a space, which helps users with visual impairments.

Common Mistakes and Misconceptions

One common mistake is using a non-breaking space (like  ) instead of a regular space. In HTML, a non-breaking space prevents the number and unit from being separated across lines, which is often desired. However, if you use a regular space, the browser might wrap the line between the number and the unit, which is acceptable but sometimes ugly. Using a non-breaking space is a good practice in web writing.

Another misconception is that the space rule only applies to SI units. In reality, it applies to all units, including imperial units like ft (feet) and lb (pounds). For example, write 6 ft, not 6ft. The same goes for time units: 5 min, 3 h, 2 s.

Some people also think that the space should be omitted when the number is a fraction or a decimal. That is not true. The space is always used, regardless of the number format: 0.5 kg, 1/2 kg (though fractions are less common).

Finally, be careful with the degree symbol for temperature. The SI recommends a space between the number and the degree symbol, but many style guides (including APA) write 25°C without a space. To avoid confusion, follow the style guide of your target publication.

Practical Tips for Consistent Writing

To ensure consistency in your writing, follow these tips:

• Use a non-breaking space (in HTML:  ) between a number and a unit to prevent line breaks.
• Set your word processor to automatically insert a space after numbers when typing units, or use a find-and-replace to add spaces.
• When in doubt, check the official SI brochure or a trusted style guide.
• For units with a prefix (like km, cm, mg), the space goes between the number and the entire unit symbol, not between the prefix and the base unit.
• In tables and figures, align numbers and units consistently, and use the same spacing throughout.

Frequently Asked Questions

Should I put a space between a number and a unit in Excel?

In Excel, if you type a number and a unit in the same cell (e.g., 5 kg), Excel treats it as text, not a number. For calculations, keep the number in one cell and the unit in a separate cell, or use a custom number format that displays the unit without affecting the value. For example, set the cell format to 0 "kg" to show 5 kg while the underlying value is 5.

Does the space rule apply to currency amounts?

For currency symbols like $, €, £, the symbol is placed immediately before the number with no space (e.g., $25). For currency codes like USD, EUR, a space is used (e.g., 25 USD). The rule is different because the symbol is a prefix, while the code is a suffix.

Is it ever correct to write “5kg” without a space?

In informal or space-constrained contexts (like labels on packaging or some web interfaces), a space may be omitted, but it is not correct according to the SI and most style guides. Always use a space in formal writing and when precision matters.

What about units like “mph” or “rpm”?

These are not SI units, but the space rule still applies: 60 mph, 3000 rpm. The space is used between the number and the unit symbol, regardless of the unit system.

How do I type a non-breaking space in Word?

In Microsoft Word, press Ctrl+Shift+Space to insert a non-breaking space. In Google Docs, you can use Ctrl+Shift+Space on Windows or Option+Space on Mac. Alternatively, copy and paste the character from a web page.

Does the space rule apply to percentages?

No, the percent sign is written directly after the number without a space (e.g., 50%). This is an exception to the general rule. Some style guides recommend a space in scientific writing (e.g., 50 %), but the common practice is no space.

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in t | Finish time | min | 50 | 0
in d | Distance | km | 10 | 0
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2