Marine General (Non-Technical)

A guide to writing Measurement Units the correct way

A guide to writing Measurement Units the correct way

I have always had issues when writing the units of measurement like whether to write 50 kW OR 50Kw or 50 KW or 50 kw. This seems to be really a silly issue but such silly things often make us feel uncomfortable.

Hence, I did an elaborate research and found some interesting stuff about the way we should write the measurement units and I am presenting the same for everyone here.

This guide is based on internationally agreed standards and represents best practice. It gives you a clean idea as to how to use and write metric units, mistakes that is usually done and ways to avoid, what to do when there is a conversion, and a very short explanation of how the metric system works.



Denotation of metric units, either alone or joint with a prefix, always starts with a lower case letter – e.g. metre, milligram, watt.

Exception: At the beginning of a sentence, the above mentioned rule is not applicable and shall start with Upper case.


The symbols for metric units are also stated in lower case – except those that are named after persons – e.g. m for metre, but W for watt (the unit of power, named after the Scottish engineer, James Watt).

Points to note:

  1. This rule applies even when the prefix symbol is in lower case, as in kW for kilowatt.
  2. Symbols meaning a million or more are written in capitals, and those meaning a thousand or less are written in lower case – thus, mL for millilitre, kW for kilowatt, MJ for megajoule (the unit of energy).
Exception: The symbol for litre (L) is an exception, I seriously don’t know why, if you know please do leave me a comment below.


While using a symbol: Symbols never pluralize, Like 25kg.

While writing in full: 25 kilograms


Never apply or use a full stop after a unit symbol. Exception : You may use a full stop if the sentence is ending after the symbol.

If there is room, leave a space between the number and the unit – e.g. 25 kg, 100 m, 37 oC.


Symbols should always be written in roman (regular upright) font and never italicized – even within surrounding italic text. This is to avoid confusion with scientific symbols.

The symbol for “per” which mean divided by is always denoted as “/” (slash). Therefore, the symbol for “kilometres per hour” is “km/h”.


Metric system is by far the best unit system to learn and write as the metric system works with a very simple logic and contains simple units and pre,suffixes.

Metric system uses prefixes which makes the job much easier like multiplying or dividing the unit by 10s, 100s, 1000s or even more. For example, the prefix “kilo-” means “1000”. So kilometre means 1000 metres, and a kilogram is 1000 grams.

Likewise, the prefix “milli” means “divided by one thousand”. So millilitre means 0.001 (one thousandth or 1/1000) of a litre, and a milligram is 0.001 (one thousandth or 1/1000) of a gram. The most common prefixes in general use are

T - tera – 1 X 000 000 000 000
G – giga – 1 X 000 000 000
M - mega – 1 X 000 000
K - kilo – 1 X 1000
H - hecto – 1 X 100
Da - deca – 1 X 10
d deci – 1 X 0.1
c centi – 1 X 0.01
m milli – 1 X 0.001
m micro – 1 X 0.000 001
n nano 
– 1 X 0.000 000 001


While using unit names in full, the prefix name and the unit name are combined to form a single word

milli + litre = milliliter
kilo + metre = kilometer
mega + watt = MegaWatt

While using symbols, the prefix symbol and the unit symbol are combined to form a single symbol

m + L = mL
k + m = km
M + W = MW


– Metric system offers plenty of choices to denote a unit; for example a unit can be written as 5000 mm OR 500 cm OR 5 m. Therefore, it is best practice to avoid large numbers or trailing zeroes which makes it difficult for people to count zeroes.

– Also, it is best practice to use whole numbers rather than decimal points of possible like 45 mm rather than 4.5 cm at the same time keeping in mind that a drawing or a paragraph denoting a single object or a project shall contain uniformity in units. Like all units used shall be in meters or cm or mm etc.


  • YES, One thing I learned was, symbols are not the same as abbreviations. Symbols such as %, $ and © are universally understood because they are independent of language.
  • Abbreviations like KPH, cc, mgw and sqm are language-dependent and possibly confusing – even in English.
  •  Standard symbols should be used in preference to invented abbreviations. In your conversation reserve the symbol m to mean “metres” – hence, avoid using the abbreviation “m” to denote “miles” or “millions” (especially where confusion is possible – e.g. on road signs)


Do you specifically write for a particular audience, like if you writing an article for an American blog then be rest assured they wont understand SI units easily as it is absolutely normal for them to follow in metric.

Conversions between metric and non-metric units are best avoided if possible as they interrupt the free flow of the sentence and distract attention. Where they are unavoidable – for example, if quoting from original material, or if the target audience is unlikely to be familiar with the source units – the following principles should be followed: In ordinary prose provide the conversion (in brackets) at first mention only. Do not convert every occurrence throughout the text.


– Mistakes often occur because of a misunderstanding of the Basic rules, These are some of the more common mistakes.

  1. Using invented abbreviations instead of correct international symbols
  2. Using a wrong symbol
  3. Pluralising symbols
  4. Writing symbols in italics
  5. Getting the case wrong – i.e. capitals instead of lower case (or vice versa)
  6. Omitting the oblique stroke (forward slash) in quoting prices
  7. Omitting the space between number and symbol (but this rule can be relaxed where there is insufficient room)

The temperature was 25CCorrect version C is the symbol for coulomb (a unit of electrical charge). Should use correct symbol. Also no space between number and symbol.The temperature was 25 ºC
The speed limit is 50KPHNon-standard abbreviation (language dependent). Should use international symbol and leave space after number.The speed limit is 50 km/h
BEACH 25KmsSymbol should be lower case and not pluralized. Should leave space between number and symbol.BEACH 2 km
Price 90p kilo“kilo” is a prefix meaning “1000”. Should use correct symbol “kg” and insert “/” to indicate correct symbol “kg” and insert “/” to indicate “per”.Price 90p/kg
Contents 5 LTRSLTRS is a clumsy, invented abbreviation. Should use symbol L (not pluralized).Contents 5 L
3kw heaterSymbol for “watt” is always upper case (capital) – even when combined with a prefix. Also there should be a space between number and symbol.3 kW heater
Printed on 90gsm paperNon-standard invented abbreviation. Should use correct symbol g/m2. Also thee should be a space between number and a symbol.Printed on 90 g/m2 paper.

About Ram Govindasamy

Ram Govindasamy is a sailing marine engineer working for a leading cruise company. Ram founded Dieselship to create an online platform for Marine engineers worldwide to bond, share knowledge & Resources. He is a computer enthusiast who loves creating web based activities, web pages & programs. He is also authoring technical articles, videos for Dieselship as well as for various other maritime websites. Ram is interested in Maritime Law and Technical Operations and looks forward to meeting new people especially those who are interested in creating web based platforms, Assets maintenance & inventory programs and Planned Maintenance software etc

One thought on “A guide to writing Measurement Units the correct way

  1. Alexander Arsenijevic says:

    The symbol for litre or liter is l, but is often written as L to prevent it from looking like the digit 1. It is also sometimes rendered in lowercase cursive form ℓ for the same reason:

    The litre, and the symbol lower-case l, were adopted by the CIPM in 1879 (PV, 1879, 41). The alternative symbol, capital L, was adopted by the 16th CGPM (1979, Resolution 6; CR, 101 and Metrologia, 1980, 16, 56-57) in order to avoid the risk of confusion between the letter l (el) and the numeral 1 (one).

    — The International System of Units (SI), 8th ed., Sec. 4.1

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