Eosinophils are also known as eosinophilic granulocytes, or eos. Eosinophils are easy to recognize in the peripheral blood because of their large bright granules.

The diameter of the eosinophil is 9-15 microns, and the nuclear to cytoplasmic (N:C) ratio is 1:3. Eosinophils are generally the largest granulocytes found in normal blood.