TCID50 Calculator

This tool calculates the TCID50 (50% Tissue Culture Infective Dose) of a virus stock using either the Reed–Muench method (Reed & Muench, 1938) or the Spearman–Kärber method (Spearman, 1908; Kärber, 1931).

Data Input

Enter your dataset including Initial Concentration / Dilution Factor / Inoculating Volume and the number of Positive / Total wells. Ensure that the observed positives are equal or decreasing and that the totals per dilution are identical. You can enter up to 1-10 test sets.

Reed–Muench Method

1. Calculate infection rate:

Infection rate = cumulative positive units / (cumulative positive units + cumulative negative units)

2. Identify dilutions above and below 50% positive, then calculate the proportionate distance (PD):

PD = (positive above 50% − 50%) / (positive above 50% − positive below 50%)

3. Calculate logID50:

logID50 = log(dilution with > 50% positive) + PD × (−log(dilution factor))

Spearman–Kärber Method

Directly estimate logID50 using the following formula:

logID50 = log(highest dilution giving 100% CPE) + 0.5 − (total number of test units showing CPE / number of test units per dilution)

Key Features

Flexible Calculation Methods:
Supports both Reed–Muench and Spearman–Kärber methods for comparison and compatibility with lab protocols.
Streamlined Data Entry:
Modern UI for easy input of dilution series, inoculating volumes, and positive/total wells.
Immediate Results:
Provides logID50 instantly with transparent calculation steps.
Reliable Workflow:
Reduces transcription and formula errors common in spreadsheet calculations.

Applications

Accurate viral titer determination for vaccine development and antiviral research.
Standardization of viral stocks across experimental batches.
Multi-site collaborative studies requiring consistent TCID50 measurement.