TCID₅₀ (Spearman–Kärber) Calculator

Enter your dilution series and positives per row. The calculator finds the last 100% positive row and computes the 50% endpoint and TCID₅₀/mL.

Assay Parameters

Starting dilution (fraction of sample) Dilution factor (fold) Wells per dilution Number of dilution rows Inoculum volume per well (mL)

Endpoint dilution (50%)

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TCID₅₀/mL

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Log₁₀(TCID₅₀/mL)

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95% Confidence (TCID₅₀/mL)

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Formula: log₁₀(endpoint) = log₁₀(D₁₀₀) − log₁₀(factor) × (Σp − 0.5)