Most abbreviations should be set without full stops:
approx Ave cf eg ie Mon vol et al
However, some organisations still commonly use stops (especially in eg and ie). Be guided by your organisation’s style guide if this is the case.
Use either no stops or 2 stops in Latin abbreviations that have 2 letters, not a single stop:
Also, do not follow these abbreviations with a comma:
eg flowering plants
not
eg, flowering plants or e.g., flowering plants
Abbreviations that require full stops
In line with accepted species nomenclature, use full stops for the abbreviations for species, both singular and plural:
sp. [singular] spp. [plural]
Use a full stop when abbreviating number to no. Without the full stop, the abbreviation may be misread, although the following number clarifies its role. No. can be used when the word number itself would be too bulky or cumbersome, or can be omitted. Other more specific words can also be used to indicate numbers within a series:
issue no. 15 issue 15
batch 65 report 23 lot 1115/A
A hash sign (octothorp) (eg #65) is also widely used to flag a following number, in citations, addresses and elsewhere.
Abbreviations that never take full stops
Do not include a full stop after unit abbreviations:
10 g 5 mL 2.5 km
See Numbers used with units for more details on units.