Hemocytometer Calculator

Calculate cell concentration and viability from hemocytometer counts.

Standard: count 4 corner squares + center
e.g. 1:2 = dilution factor 2
Please check your inputs and try again.

Where the 104 Comes From

The hemocytometer's conversion factor looks arbitrary but follows directly from the chamber's dimensions. Each large corner square is 1 mm × 1 mm, and the coverslip sits 0.1 mm above the grid.

Volume per square = 1 × 1 × 0.1 = 0.1 mm³ = 10−4 mL
cells/mL = (mean count per square) × 104 × dilution factor

So counting one square and multiplying by 10,000 converts to a per-millilitre concentration. Everything else — averaging squares, dilution — is refinement on that base relationship.

Count per squareAssessment
< 20Too few — unreliable, concentrate the sample
20–50Ideal range
> 100Too crowded — dilute and recount

Counting statistics set that range. Cell counts follow a Poisson distribution, so the relative error is roughly 1/√n. Counting 100 cells gives about 10% precision; counting 400 gives 5%. This is why several squares are averaged rather than one.

Viability and the Boundary Rule

Trypan blue is excluded by intact membranes, so blue cells are dead. Note this measures membrane integrity specifically — a cell committed to apoptosis may still exclude the dye and be scored as viable, so trypan blue overestimates viability in apoptotic populations.

The boundary convention exists to avoid double counting: include cells touching the top and left lines, exclude those touching the bottom and right. Applied consistently, each cell is counted exactly once across adjacent squares.

Worked Examples

Example 1: 180 cells in 4 squares, dilution 1:2
conc=180/4/1e-4×2
Result: 9×10⁵ cells/mL
Typical exponential-phase culture density
Example 2: Trypan blue: 160 live/180 total
Viability=160/180=88.9%
Result: Acceptable for most experiments
Below 90% — consider fresh culture
Example 3: Counting precision
100 cells counted versus 400 cells
Result: About 10% versus 5% error
Poisson statistics give relative error near 1/√n. Counting more squares is the simplest way to improve precision.
Example 4: Why dilution factor is easy to miss
1:1 trypan blue mix, 45 cells per square
Result: 4.5 × 105 × 2 = 9 × 105 cells/mL
The stain itself dilutes the sample twofold. Reporting without that correction halves the true concentration.

Common Mistakes

⚠️
Counting outside the 20–50 per square range

Too few cells gives poor Poisson precision; too many makes accurate counting impossible. Adjust dilution to land in the ideal range.

⚠️
Applying the boundary rule inconsistently

Include cells on the top and left borders, exclude bottom and right. Inconsistency causes systematic over- or under-counting.

⚠️
Forgetting the dilution factor

Trypan blue is usually mixed 1:1 with sample, giving a dilution factor of 2. Omitting it halves the reported concentration.

⚠️
Treating trypan blue exclusion as full viability

It measures membrane integrity only. Early apoptotic cells still exclude the dye, so viability is overestimated in apoptotic cultures.

Frequently Asked Questions

Trypan blue exclusion?
Dead cells take up trypan blue (blue). Live cells exclude it (clear/white). Add equal volume 0.4% trypan blue to cells, load hemocytometer, count immediately (dye penetrates all cells if left too long).
Why count multiple squares?
Counting error decreases with more cells counted. Count ≥200 cells for <10% CV. Count all 5 large squares (4 corners + center) for best accuracy. If too many cells: dilute more. Too few: dilute less.
Why multiply by 104?
Each large square holds 0.1 mm³, which is 10−4 mL. Multiplying the count per square by 10,000 converts to cells per millilitre.
How many cells should I count per square?
Between 20 and 50. Fewer gives poor statistical precision; more makes accurate counting difficult. Adjust the dilution to reach this range.
Does trypan blue measure true viability?
It measures membrane integrity. Early apoptotic cells still exclude the dye, so viability is overestimated in populations undergoing apoptosis.
What is the boundary counting rule?
Count cells touching the top and left lines, exclude those on the bottom and right. This prevents counting the same cell in two adjacent squares.