Measurements are sometimes common enough that their abbreviated forms do not need to be explained. When reporting common measurements in abbreviated form, the full stop is often (but not always) omitted, except of course if the abbreviation is the last word in a sentence.
We used 250ml per trial. This drive has 100Gb of storage. The distance travelled was 153km.
The thermal protocol was a single cycle at 96°C for 1 min, 25 cycles at 96°C for 10 s, 50°C for 5 s and 60°C for 4 min.
In science and engineering, it is often a good idea to spell out less common measurements the first time that the term is used, or to list all such measurements in a glossary near the beginning of the text.
An approximately 710-base pair (bp) fragment of the COI gene was amplified.