# units of measurement

Use numerals with units of measurement and time in technical papers and reports, even when the number is less than 10. In some outreach publications, you may spell out numbers less than 10, especially with units of time.

Except with $, °, and %, leave a space between the numeral and the unit. Include a hyphen between a numeral and an abbreviated unit when the value is used as an adjective.

Do not include a period after a unit symbol except at the end of a sentence. The exception to this rule is inches (which are abbreviated “in.”).

2 kW | 7 cm^{2} |
16.8% | |

3 m | 8-hour days | 300 Btu | |

5 years | $2 billion | 45° | |

4 in. | a 15-MW turbine | 65°C |

Avoid nonstandard abbreviations such as sec or cc, and instead use standard abbreviations
such as s and cm^{3}. Unless your profession, technical field, or scientific discipline specifies something
different, use the abbreviations in NREL's list of technical abbreviations or the National Institute of Standards and Technology (NIST) guide.

Use a center dot to indicate multiplication of units (such as N∙m for Newton-meters),
and use a slash or negative exponent to indicate division. For example, 344 meters
per second can be written as 344 m·s^{−1} or 344 m/s.

Format variables in italic type and units in roman type:

*t*= 3 s, where

*t*is time and s is seconds

Incorrect: t = 3 s, where t is time and s is seconds

Incorrect: 20 mL of water/kg

When expressing a range, repeat the unit symbol if it is closed-up with the numeral ($, °, %):

100°C–105°C

60°–90° (example of angular measurements)

$40–$60/MWh

Refer to the NIST style conventions checklist for additional style tips and examples.

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