MOI (Multiplicity of Infection) Calculator

In virology and gene therapy research, Multiplicity of Infection (MOI) is the ratio of infectious viral particles to target cells — a critical value for controlling how many cells get infected and how efficiently. Enter your Number of Cells, Viral Titer, and Volume into the MOI Calculator to get the MOI value, total infectious units, and Poisson-derived probabilities for infection, no infection, and multiple infections per cell. Optionally enter a Target MOI and Number of Wells to reverse-calculate the viral volume needed for your experiment.

Total number of target cells

units/mL

Concentration of infectious units (PFU, TU, IFU)

mL

Volume of viral solution added

Desired MOI for reverse calculation

minutes

Duration of virus-cell contact period

For multi-well plate calculations

Results

MOI (Multiplicity of Infection)

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Total Infectious Units

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Infection Probability

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Uninfected Cells (%)

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Multiple Infection (%)

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Frequently Asked Questions

What is MOI (Multiplicity of Infection)?

MOI is the ratio of infectious agents (viruses, phages) to target cells in a defined volume. It represents the average number of viral particles that could potentially infect each cell. For example, MOI = 1 means there's an average of 1 virus per cell.

Which titer should I use (TU/PFU/IFU, etc.)?

Use the titer that represents functional, infectious units for your specific system. PFU (plaque-forming units) for bacteriophages, TU (transducing units) for lentiviruses, or IFU (infectious units) for other viral systems. Avoid using genome copies (vg/mL) as they don't represent infectious particles.

How does MOI relate to infection rate?

The relationship follows Poisson statistics. At MOI = 1, approximately 63% of cells get infected. At MOI = 0.3, about 26% of cells are infected, while at MOI = 3, about 95% are infected. Higher MOI increases infection rate but also increases multiple infections per cell.

Can I calculate MOI with vg/mL (genome copies)?

It's not recommended. Genome copies include non-infectious particles, leading to overestimated MOI values. Always use functional titers (PFU, TU, IFU) that represent actual infectious capacity for accurate MOI calculations.

What infection rate corresponds to MOI 0.3?

MOI 0.3 corresponds to approximately 26% infection rate according to Poisson distribution. This is often used when you want single infections with minimal multiple infections per cell, common in clonal selection experiments.

Will this calculation guarantee the desired outcome?

MOI is a guide based on theoretical models. Actual outcomes depend on experimental conditions, cell state, viral stability, adsorption efficiency, and assay methods used for titer determination. Always validate with pilot experiments.

How do I handle very small volumes in calculations?

For volumes smaller than minimum pipettable amounts (typically 0.5-1 μL), consider serial dilutions or prepare larger volumes for multiple experiments. The calculator shows when volumes become impractical for standard pipetting.

What's the difference between actual MOI and theoretical MOI?

Theoretical MOI is calculated from input values assuming perfect conditions. Actual MOI accounts for factors like viral adsorption efficiency, cell viability, and time-dependent viral decay. The theoretical calculation provides a starting point for optimization.