There is only one positive way to check wire gauge; that is by micrometer, as illustrated. The careful buyer checks the gauge of both warp and shute wires.
Measurer the clear open space between parallel wires. Example illustrates 1/2″ clear opening.
“Mesh” means the number of openings per lineal inch. To determine the mesh measure from the centre of a wire to a point one inch distant and count the intervening openings. For coarser meshes count over four inches and average the count.