Get your writing right – Part 4 – Units outside the SI

Certain units are not part of the SI, but are so widely used that they are generally accepted within scientific writing.

A few of the units in this category are shown in Table 4.

Table 4 Units accepted for use with the SI


Physical quantity Name Symbol Value
Time minute min (not mins) 1 min = 60 s
Time hour h 1 h = 3600 s
Time day d 1 d = 86,400 s
Temperature degree celsius °C °C = K-273.15
Mass tonne t is often used 1 tonne = 103 kg

Note that so-called ‘imperial units’ (e.g. inch, foot, yard, gallon) are no longer acceptable in scientific writings or reports although you might still come across such units in ‘everyday life’. See Appendix 1 for more examples of common units and their SI equivalents.