One of the most important factors when picking out a cast net is the mesh size (mesh size is the spacing between the individual strands of line that form the netting). It is important to consider two factors when picking out mesh size.
1. How fast do I want the net to sink? Why does this matter, doesn't the amount of lead determine the sink rate? Nope...
Smaller mesh size creates more webbing and causes a net to sink much slower. Larger mesh creates less webbing and allows a net to sink quicker.
2. What kind of baitfish will be the primary target? To small of mesh and larger baitfish may blow through the mesh, or simply swim under a slow sinking net. Mesh to large and smaller baitfish may "gill off" creating a huge mess and a lot of wasted bait. Smaller mesh tends to catch more, but too small and it may catch baitfish too small or of no use. (Beginner Suggestion- Start with a 3/8" mesh cast net for a good all around net)
Mesh size may be listed two ways "square" or "stretched". Square mesh size is the most common measurement, it is very simply the size of the mesh squares. Stretched mesh is the length of those squares when they are, you guessed it...stretched out.
Common Cast Net Mesh Sizes and suggested uses are as follows. Of course these are suggestions, and may vary depending on the size of baitfish in a given area or season.
3/16" Square (3/8" Stretched)-Glass Minnow
1/4" Square (1/2" Stretched)-Minnow
3/8" Square (3/4" Stretched)-Small Pilchard/Finger Mullet
1/2" Square (1" Stretched)-Sardine
1.25" Square (2.5" Stretched)-Mullet