Standard Wire Gauge is the system used in the industry of measuring wire by diameter. Usually abbreviated to S.W.G.

common uses of mesh and netting.

Less than 22 gauge -       
Fine Stainless woven Mesh:
Material and chemical Filtration

22 gauge - 0.7 mm diameter
Chicken wire of 13 mm aperture:
Uses: Poultry enclosures and fruit cages, Sculpting.
Fine welded or woven mesh:
Uses: Rodent protection and wild bird feeders.

20 gauge - 0.9 mm diameter - 
Chicken wire 19mm & 25mm aperture:
Uses: Poultry enclosures, Roof thatching, Loft insulation mesh

19 gauge - 1 mm diameter
Chicken wire of 50 mm aperture:
Uses: Poultry enclosures.
Rabbit netting of 31 mm aperture:
Uses: Rabbit protection
Welded mesh 13mm – 25mm:
Uses: Small bird aviaries, pet rabbit runs etc.

16 gauge - 1.6 mm diameter
Welded mesh 13– 20 mm aperture
Uses: Rodent cages and parakeet aviaries.
Welded mesh 25mm aperture
Uses: Cat Enclosures, Squirrel Protection,
Birds of Prey Aviaries. Tree guards.
Welded mesh 50 mm aperture
Uses: Garden fencing. Small-dog enclosures.
Woven Stainless steel 6 – 13mm.
Uses: Car radiator grills. Filtration,

14 gauge - 2 mm diameter
Welded mesh 25 mm aperture.
Uses: Parrot Aviaries, Machinery guards.
Welded mesh 50 mm aperture.
Uses: Garden fencing. Medium-dog enclosures,
Sheep, Deer & Goat fencing.

12 gauge - 2.6 mm diameter
Welded mesh 50 mm aperture:
Uses: Security Fencing, Garden fencing.
Large-dog enclosures.  Sheep, Deer & Goat fencing.

10 gauge - 3 mm diameter
Welded mesh 50 mm aperture
Uses: Security Fencing,
Strong Garden fencing. Large-dog enclosures.