What this is for: Endpoint titration analysis — log10 TCID50/mL from wells positive/total per dilution, with a Reed–Muench cross-check and a PFU/mL conversion.
The formula: log10 TCID50 = L + d × (S − 0.5), L = log of lowest all-positive dilution, d = log step, S = sum of positive proportions
How to use:
- Enter the inoculum volume per well in mL and the dilution step in log₁₀ units.
- Enter the log₁₀ dilutions least-dilute first — the first row should ideally be 100% positive.
- Enter the wells positive and wells total in the same order as the dilutions.
- Read S, log₁₀ TCID50/mL, TCID50/mL, and the approx. PFU/mL equivalent.
TCID50 Calculator — Spearman–Kärber Method
Enter each dilution as a log10 exponent (e.g. -6 = 10^-6 dilution), with the number of positive wells and total wells inoculated at that dilution. The FIRST row must be the least-dilute (most concentrated) dilution, ideally 100% positive. log10 TCID50/mL = -(first log dilution) + (S - 0.5) × log step - log10(inoculum volume in mL), where S = sum of proportions positive.
mL
S = sum of proportions positive
log10 TCID50 / mL
TCID50 / mL
Approx. PFU/mL equivalent (× 0.69)
| log10 dilution | Wells positive | Wells total | Proportion positive |
|---|
Prefer to work offline or keep a copy? The download link is right below.
Download the TCID50 Calculator (Spearman–Kärber) workbook (.xlsx)
Download the TCID50 Calculator (Spearman–Kärber) workbook (.xlsx)
Notes & limits (from the workbook): Enter each dilution as a log10 exponent (e.g. -6 = 10^-6 dilution), with the number of positive wells and total wells inoculated at that dilution. The FIRST row must be the least-dilute (most concentrated) dilution, ideally 100% positive. log10 TCID50/mL = -(first log dilution) + (S - 0.5) × log step - log10(inoculum volume in mL), where S = sum of proportions positive. The PFU/mL equivalent uses the approximate × 0.69 conversion.