Non-zero kerf thicknesses (the reality of laser cutting) mean that holes have a larger diameter and edges are further inside than you've designed in CAD or Illustrator.

Kerf charts exist! Many manufacturers will provide kerf values for the materials they create. 

However, kerf can vary from cutter to cutter and material batch to material batch; it depends on real material thicknesses, how defocused the laser is, and how precise the laser beam is. The best thing to do is test a small sample of the material yourself (using something simple like a 1" x 1" square) and measure it. Take several measurements and average them to get a very good, local, immediate approximation of the kerf.