Units of Measure

  1. Metric (also called the international system of units, or SI) should be the default unit of measure. Where appropriate, the imperial conversion may appear afterwards in parentheses. Exceptions can be made when communicating with particular audiences.

    Removals were estimated to be 566.1 m3/d (3.56 106 bbl/d).

  2. When using an abbreviated unit of measure, you must always use numerals as opposed to writing the number out.

    The rupture released 5 m3 of produced water.

    Not: The rupture released five m3 of produced water.

    But: The rupture released five cubic metres of produced water.

  3. Always put a space between the number and the unit of measure, except for per cent (%) and degrees (°).

    13 km; 5 bbl/d

    But: 15%; 30°C

    Best practice is to put a nonbreaking space between the number and its unit so that they do not get separated at the end of a line. In Microsoft products, use Ctrl+Shift+Space to insert a nonbreaking space. See the Tools of the Trade section for shortcuts like this.

  4. Never pluralize an abbreviated unit of measure.

    The pipeline is 5 km long.

    The pipeline is 5 kilometres long.

  5. Large numbers typically use scientific notation (e.g., 103 = thousand).

    1. Exponents should usually be divisible by 3.

      15.3 103 m3 is preferred over 1.53 104 m3

    2. Never use ex notation. Most nonindustry stakeholders will have never seen this usage before.

      2.4 103 never 2.4 e3

    3. Where reasonable, consider writing large numbers out, especially in executive summaries or other contexts meant for nonindustry stakeholders.

      Technically correct: 5.3 106 m3

      Preferred in many contexts: 5.3 million cubic metres

Common SI units used at the AER (not exhaustive)
Name Symbol
kilogram kg
metre m
mole mol
pascal Pa
second s
SI prefixes
Factor Name Symbol
1024 yotta Y
1021 zetta Z
1018 exa E
1015 peta P
1012 tera T
109 giga G
106 mega M
103 kilo k
102 hecto h
101 deca da
10−1 deci d
10−2 centi c
10−3 milli m
10−6 micro µ
10−9 nano n
10−12 pico p
10−15 femto f
10−18 atto a
10−21 zepto z
10−24 yocto y