I did my PhD in the Department of Chemical Engineering at Imperial College London. My research focused on mathematical modeling of the cell cycle in leukemia and involved experiments with cell lines. During that time, I had to count cells with a hemocytometer so often to track growth that I got tired and decided to build an app, HemocyTap, and share my knowledge on the topic here to help as many people as possible.

Why are there different hemocytometer grid sizes?

The hemocytometer was originally invented by Louis-Charles Malassez to count blood cells. But later on, biologists and experimental doctors discovered that it could be applied to other areas, to count yeast, sperm, and other types of human and animal cells. A hemocytometer with a different grid to account for smaller particles became necessary (as bigger hemocytometer squares meant more cells to count per area unit but also less guiding lines for the count – so more errors).

The current hemocytometer is composed of nine equally sized bigger squares. The central one is different from the other ones because it is divided into 25 smaller squares, while the ones in the corners are divided into 16 smaller squares. The rest of squares are not used. In addition, the smaller squares inside the central square are subdivided into 16 even smaller squares each. This allows to count very tiny cells with the same precision level as larger ones (but with a higher magnification).

What size to use with my cell type?

Let’s go through the maths – and then, if you know what the average size (diameter) of your cell is, you can tell yourself. I’ll just give the most common examples.

The main piece of information you should remember is this: each of the 9 squares in a chamber is 1mm in width (or 1mm2 in area, as it’s a square).

Corner squares – WBC

For the corner squares, each of the 16 smaller squares will be 1 mm/4 = 0.25 mm in width and 0.25 mm x 0.25 mm = 0.0625 mm2 in area (or 1 mm2/16 = 0.0625 mm2). Therefore, cells that are 10 μm or more should be counted in these corner squares (although it doesn’t hurt if you also include a count from the central square). For example, white blood cells (leukocytes) satisfy this criterion.

hemocytometer corner square size hemocytometer corner square area

Central square – RBC, yeast, sperm cells…

For the central square, each of the 25 smaller squares will be 1 mm/5 = 0.2 mm in width and 0.2 mm x 0.2 mm = 0.04 mm2 in area (or 1 mm 2/25 = 0.04 mm2). In turn, each of the 25 smaller squares contains 16 even smaller squares which measure: 0.2 mm/4 = 0.05 mm in width and 0.05 mm x 0.05 mm = 0.0025 mm2 = 2500 μm2 (or 0.04 mm2/16 = 0.0025 mm2). Cells that are 10 μm or smaller should be counted in the central square – sometimes even in one of the smaller squares inside the central square. Typically you would count red blood cells, platelets, most types of yeast, and sperm cells.

hemocytometer central square sizehemocytometer central square area

So what about your cells? did you decide in which square type you0re going to count them?

Surface to volume

This step is super easy, but I’m going to make it even easier with a summary table. Just keep in mind that the vertical distance between the slide and the chamber is always 0.1 mm, multiply your area by 0.1 mm and you will be fine.

Unit Width Area Volume (mm3) Volume (mL) # per
chamber 3 mm 9 mm2 0.9 mm3 0.0009 mL 2 per hemocytometer
small sq. 1 mm 1 mm2 0.1 mm3 0.0001 mL 9 per chamber
corner sq. 1 mm 1 mm2 0.1 mm3 0.0001 mL 4 per chamber
smaller sq. 0.25 mm 0.0625 mm2 0.00625 mm3 0.00000625 mL 16 per corner square
central sq. 1 mm 1 mm2 0.1 mm3 0.0001 mL 1 per chamber
smaller sq. 0.2 mm 0.04 mm2 0.004 mm3 0.000004 mL 25 per central square
even smaller sq. 0.05 mm 0.0025 mm2 0.00025 mm3 0.00000025 mL 16 per smaller square

And last but not least: you should divide by the volume above in your hemocytometer calculation! That will give you the cells per mL.


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