1. An instrument for counting the blood cells in a measured volume of blood.
2. A device used in manual blood counts, consisting of a microscopic slide with a depression whose base is marked in grids, and into which a measured volume of a sample of blood or bacterial culture is placed and covered with a cover glass.

The number of cells and formed blood elements in the squares is counted under a microscope and used as a representative sample for calculating the unit volume; also called, counting cell, counting chamber, and hemocytometer.