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Expressing Quantities

Units of Measure

Phil B. Fontanarosa

and Stacy Christiansen

Expressing Quantities

Arabic numerals are used for quantities with units of measure (see 19.1, Numbers and Percentages, Use of Numerals). By SI convention, it is preferable to use only numbers between 0.1 and 1000 and to use the appropriate prefix for expressing quantities. For example, 0.003 mL is expressed as 3 μL; 15 000 g is expressed as 15 kg.

Some clinical measurements are expressed in quantities and units that may have numbers outside this preferred range. For such values, the use of scientific notation is acceptable.

20 000 000 A may be expressed as 20 million amperes or as 2 × 107 A

Reported SI values should follow recommendations for preserving the proper number of significant digits. (See 20.8.2, Study Design and Statistics, Significant Digits and Rounding Numbers, Rounding.) The use of these increments is intended to eliminate reporting results beyond the appropriate level of precision.

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