Hemocytometer Calculator

Fundamentals of Cell Counting

Manual cell counting with a hemocytometer remains the gold standard for determining cell concentration and viability in research laboratories.

cells/mL = (total cells counted / squares counted) $\times$ dilution factor / (volume per square in mL)

Key principles: • Volume: Each large square on an Improved Neubauer has dimensions 1 mm $\times$ 1 mm $\times$ 0.1 mm = 0.1 µL = 1 $\times$ $10^{-4}$ mL • Counting convention: Include cells on the top and left borders; exclude those on the bottom and right • Minimum count: At least 100 cells total for acceptable precision (CV < 10%) • Viability: Trypan blue exclusion distinguishes live (clear) from dead (blue) cells

Common Pitfalls in Cell Counting

Several errors can lead to inaccurate hemocytometer counts:

• Cell clumping: Inadequate mixing or over-trypsinization leads to clumps that are hard to count accurately. Pipette gently 8–10 times before loading. • Overfilling the chamber: Excess volume lifts the coverslip, increasing the effective depth and overestimating concentration. Load exactly 10 µL per side. • Counting too few cells: Counting fewer than 100 total cells introduces large sampling error. Count more squares or adjust dilution. • Trypan blue exposure time: Prolonged exposure (>5 minutes) kills viable cells, artificially lowering viability readings. Count within 3–5 minutes. • Air bubbles: Bubbles under the coverslip distort the grid and trap cells. Reload the chamber if bubbles are present. • Wrong dilution factor: Forgetting to account for the trypan blue dilution (usually 2×) will underestimate the true concentration by half.