MOI Calculator
Virus Type
Total Cells ?
Vessel Preset (click to auto-fill cells)
Virus Titer (PFU/mL) ?
Titer Unit
Desired MOI ?
Tip: At MOI = 1, only ~63% of cells are infected (Poisson). Use MOI 3 for ~95% or MOI 5 for ~99.3% infection efficiency.
50.0
µL virus stock needed
for MOI 5
99.3%
Cells Infected
0.7%
Uninfected
95.9%
Multi-Infected
5.0
MOI
Poisson Infection Distribution
MOI vs Infection Efficiency
Poisson Probability Table
k (viruses/cell) P(k) % of Cells Cells (est.)
Vessel Scaling Reference
Vessel Typical Cells Volume Needed

About the MOI Calculator

The multiplicity of infection (MOI) calculator helps virologists, gene therapy scientists, and cell biologists determine the correct amount of virus stock to add to their cell cultures. MOI is defined as the ratio of infectious virus particles to target cells: MOI = (titer × volume) / cell count. Because viral particles distribute randomly among cells following a Poisson process, the fraction of cells that receive at least one virus particle is 1 − e−MOI. This means that at MOI = 1, approximately 36.8% of cells remain uninfected, and achieving greater than 95% infection requires MOI ≥ 3.

This free online MOI calculator supports all common virus types used in research and manufacturing: lentiviral vectors for stable gene delivery and CAR-T cell engineering, adenovirus for high-efficiency transient transduction, adeno-associated virus (AAV) for gene therapy applications, baculovirus for insect cell expression systems (BEVS), retrovirus for stable integration, vaccinia for vaccine production, and bacteriophage for microbiology research. The calculator accepts titer in PFU/mL, TU/mL, IU/mL, vp/mL, vg/mL, or TCID50/mL and provides the Poisson probability distribution, infection efficiency curve, and vessel scaling table for experiment planning from 96-well plates to production bioreactors.

For baculovirus-specific infection planning including time of infection (TOI) optimization and harvest window prediction, see the dedicated TOI/MOI Optimizer. For AAV titer unit conversions between vg/mL, GC/mL, capsids/mL, and TU/mL, use the AAV Titer Unit Converter.

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Frequently Asked Questions

What is multiplicity of infection (MOI)?

Multiplicity of infection (MOI) is the ratio of infectious virus particles to target cells. An MOI of 1 means one infectious particle per cell on average. Because viruses distribute randomly among cells following a Poisson distribution, at MOI = 1 approximately 63.2% of cells receive at least one virus, while 36.8% remain uninfected. Higher MOI values increase the fraction of infected cells but also increase the proportion of multiply-infected cells.

How do I calculate MOI from virus titer and cell count?

MOI = (virus titer in PFU/mL or TU/mL) × (inoculum volume in mL) / (total number of cells). For example, if you add 0.5 mL of a 1 × 108 PFU/mL stock to 1 × 106 cells, the MOI = (1e8 × 0.5) / 1e6 = 50. To calculate the volume needed for a target MOI, rearrange: Volume (mL) = (MOI × cell count) / titer.

What MOI should I use for lentiviral transduction?

For lentiviral transduction of easy-to-transduce cells like HEK293T, an MOI of 1-5 is typically sufficient. For primary cells, T cells, or stem cells, higher MOIs of 5-20 may be needed due to lower permissiveness. For CAR-T manufacturing, MOI 3-10 is common. Start with a range (e.g., MOI 1, 5, 10, 20) and optimize by measuring transduction efficiency via flow cytometry for reporter gene expression at 48-72 hours post-transduction.

Why does the Poisson distribution apply to viral infection?

Virus particles distribute randomly among cells during infection, which follows a Poisson process. The probability that a cell receives exactly k virus particles is P(k) = e-MOI × MOIk / k!. This means even at MOI = 1, some cells get 0, some get 1, some get 2 or more viruses. The key prediction: the fraction of uninfected cells = e-MOI, so at MOI 1 about 36.8% escape infection. This is why MOI 3-5 is needed for near-complete infection (95-99%).

What is the difference between MOI based on PFU and MOI based on vg?

PFU-based MOI (plaque-forming units) counts only infectious particles, while vg-based MOI (viral genomes) counts all genome-containing particles regardless of infectivity. For AAV, the vg-to-infectious particle ratio is typically 100:1 to 10,000:1, meaning an MOI of 100,000 vg/cell might correspond to only 10-1,000 infectious events per cell. Always specify which unit your MOI is based on. For lentivirus and adenovirus, TU/mL (transducing units) is the standard functional titer unit.

How do I scale MOI calculations from well plates to bioreactors?

MOI is cell-number-based, so scaling is straightforward: keep the same MOI and multiply virus volume proportionally. Volume = MOI × total_cells / titer. If you used MOI 5 with 1 × 106 cells in a 6-well plate, scaling to 2 × 109 cells in a 10 L bioreactor requires proportionally more stock. Key scale-up considerations: virus stock concentration (you may need to concentrate for large volumes), addition time, mixing uniformity, and adsorption kinetics at higher cell densities.