Hong Life CalculatorsUnderstanding the hemocytometer cell count calculator — concept and principle
A hemocytometer is a thick glass slide with a counting chamber of known depth and an engraved grid. Counting the cells in a few squares under the microscope, usually after mixing with trypan blue, gives the cell concentration, the viability and the total number of live cells. These numbers are needed before seeding plates, passaging cultures or preparing cells for transfection and flow cytometry.
How it is calculated
- Live cells/mL = (live cells counted ÷ squares counted) × dilution factor × 10⁴
- Viability = live ÷ (live + dead) × 100%
- Total live cells = live cells/mL × total volume (mL)
The squares are the large 1 mm × 1 mm corner squares of a standard improved Neubauer chamber. The dilution factor includes the trypan blue dilution: mixing equal volumes of cells and dye gives a factor of 2.
The principle
Each large square has an area of 1 mm² and the chamber is 0.1 mm deep, so the liquid above one square is 0.1 mm³ = 0.1 µL = 10⁻⁴ mL. The average count per square is therefore the number of cells in 10⁻⁴ mL, and multiplying by 10⁴ converts it to cells per mL. Trypan blue is excluded by cells with intact membranes and enters dead cells, staining them blue; live cells stay bright and unstained. Counting is a sampling process that follows Poisson statistics, so the relative error is about 1 ÷ √(cells counted).
Worked example
- Inputs: 180 live and 20 dead cells in 4 squares, dilution factor 2, total volume 10 mL.
- Average live cells per square = 180 ÷ 4 = 45.
- Live cells/mL = 45 × 2 × 10⁴ = 900,000 (9.0 × 10⁵ /mL).
- Viability = 180 ÷ 200 × 100 = 90%.
- Total live cells = 900,000 × 10 = 9,000,000.
| Squares counted | Live cells/mL |
|---|---|
| 1 | 3,600,000 |
| 2 | 1,800,000 |
| 3 | 1,200,000 |
| 4 | 900,000 |
| 5 | 720,000 |
| 6 | 600,000 |
| 8 | 450,000 |
How to read the result
Healthy, actively growing cultures typically show high viability, often above 90%; a falling viability signals stress, over-confluence or harsh handling. With 180 cells counted the counting error is about 1 ÷ √180 ≈ 7%. A few hundred cells per count gives a reasonable precision; if each square holds very few cells, count more squares, and if cells overlap, dilute further.
Common mistakes
- Forgetting to include the trypan blue dilution in the dilution factor.
- Counting the small central squares while using the 10⁴ factor for large squares.
- Counting cells on all four border lines, which overestimates; count two sides only.
- Leaving cells in trypan blue too long, which stains live cells too.
Frequently asked questions
What if I count all 9 large squares?
Enter 9 as the number of squares; the average per square and the 10⁴ factor stay the same.
How do I count cells touching the lines?
A common rule is to count cells touching the top and left lines and exclude those touching the bottom and right lines.
Sources: Strober, W., Trypan blue exclusion test of cell viability, Current Protocols in Immunology (Wiley) · Freshney, R. I., Culture of Animal Cells: A Manual of Basic Technique and Specialized Applications (Wiley)