Cell Viability Calculator
Cell viability measures the proportion of living cells in a population and is a fundamental quality control parameter in cell biology. The formula is: viability (%) = (live cells / total cells) x 100. You can enter live cell count and dead cell count (the calculator sums them for total), or enter live cell count and total cell count directly. This tool is useful for trypan blue exclusion assays on a hemocytometer, flow cytometry live/dead gating, and MTT/MTS assay normalisation.
Cell viability formula
Viability (%) = live cells / (live + dead cells) x 100
Mortality (%) = 100 - viability (%)
For trypan blue: count cells in a defined grid area (typically all 4 corner squares of a hemocytometer), distinguish clear (live) from blue (dead), and enter counts here.
Viability guidelines for common applications
- Routine subculture: viability above 90% is standard. Below 80%, identify the cause before continuing.
- Transfection: recommend above 95% for optimal efficiency.
- Primary cell culture: aim for above 90%; primary cells are more sensitive to stress.
- Cryopreservation post-thaw: typically 70-90%; some loss is expected.
- Drug toxicity IC50 assay: viability measured at each drug concentration to build dose-response curve.
Frequently asked questions
What is cell viability?
Cell viability is the proportion of live cells in a cell population, expressed as a percentage: viability (%) = (live cells / total cells) x 100. It is a critical quality control metric in cell culture, drug toxicity assays, and biopharmaceutical manufacturing.
What is trypan blue exclusion?
Trypan blue is a dye that is excluded by live cells with intact membranes (live cells appear clear). Dead or damaged cells with compromised membranes take up trypan blue and appear blue under a microscope. Counting blue vs. clear cells gives live and dead counts for viability calculation.
What cell viability is acceptable for experiments?
Most cell culture experiments require at least 90% viability for meaningful results. For sensitive assays such as primary cell culture, co-culture, or transfection, 95% or higher is preferred. Below 80% viability, results may be unreliable due to stress-induced changes in cell behaviour.
How does this differ from cell counting by hemocytometer?
A hemocytometer counts cells per mL by physical counting under a microscope. Cell viability is a separate calculation from those counts: you count total cells and distinguish live from dead (e.g., by trypan blue). This calculator computes viability from whichever counts you have, whether from a hemocytometer or flow cytometry.
What is the difference between cell viability and cytotoxicity?
Cell viability measures the fraction of live cells in a treated population. Cytotoxicity is usually expressed relative to an untreated control: cytotoxicity (%) = 100 - (viability of treated / viability of control x 100). This calculator computes absolute viability; cytotoxicity requires a second reference measurement.
Official sources
- NIH/NCBI: Cell viability assay methods review.
- FDA: FDA biological product guidelines (cell-based therapies).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.