In the USA, ion exchange resin bead size is often expressed in mesh. This table shows the corresponding sieve opening in millimetres. Historically, there were other mesh definitions (such as Tyler or BSS), but they are no longer in use.

Most commercial resins have a particle size of 0.3 to 1.2 mm, which corresponds to 16 to 50 mesh (US). Uniform resins such as Amberjet^TM, Dowex Monosphere^TM or Lewatit Monoplus^TM have a much narrower particle size distribution. Chromatographic grade resins are usually finer (150 to 300 µm i.e. 50 to 100 mesh) with a narrow distribution as well.