Enter virus titer, cell count, and desired MOI. Get the exact volume to add, Poisson infection probabilities, and a step-by-step dilution protocol. Data never leaves your browser.
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Load example MOI data to see the full workflow
MOI 5–10 is standard for most cell lines. Polybrene (4–8 µg/mL) improves transduction.
Volume Required
Add to each well
15.0 µL
of Lentivirus stock at 1.0 × 10^8 TU/mL
1.5 × 10^6
Total particles
MOI 5
Target ratio
Infection Probabilities
At MOI 5: 99.3% of cells receive ≥1 virus particle
Cell Infection Simulation
| k | P(X=k) | % |
|---|---|---|
| 0 | 0.0067 | 6.7e-1% |
| 1 | 0.0337 | 3.4% |
| 2 | 0.0842 | 8.4% |
| 3 | 0.1404 | 14.0% |
| 4 | 0.1755 | 17.5% |
| 5 | 0.1755 | 17.5% |
| 6 | 0.1462 | 14.6% |
| 7 | 0.1044 | 10.4% |
| 8 | 0.0653 | 6.5% |
| 9 | 0.0363 | 3.6% |
| 10 | 0.0181 | 1.8% |
| 11 | 0.0082 | 8.2e-1% |
| 12 | 0.0034 | 3.4e-1% |
| 13 | 0.0013 | 1.3e-1% |
| 14 | 0.0005 | 4.7e-2% |
| 15 | 0.0002 | 1.6e-2% |
1Add virus stock directly to cells
When to use
Do not use for
At MOI = 1, 36.8% of cells remain uninfected. At MOI = 3, ∼5% escape. At MOI = 5, <1%. Doubling MOI beyond 5 wastes virus without meaningfully increasing transduction efficiency — but it does increase toxicity and multiple-integration events.
Lentivirus: MOI 5–10 for most cell lines. Adenovirus: MOI 50–500. AAV: MOI 10,000–500,000 (vg-based, not infectious). Using a lentivirus MOI for AAV will yield zero transduction; using an AAV MOI for lentivirus will kill every cell.
If the calculated virus volume exceeds well capacity, you cannot simply add more — you must concentrate the stock or reduce cell number. Conversely, if the volume is sub-microliter, you need an intermediate dilution to maintain pipetting accuracy.
Rapidly dividing cells can double in 18–24 hours. If you plate 100,000 cells today and infect tomorrow, the actual cell count at infection may be 150,000–200,000 — cutting your effective MOI by 30–50%. Always count at the time of virus addition.
Poisson distribution model: P(k) = (MOI^k e^⁻MOI) / k!. Calculates exact virus volume, expected infection probabilities (uninfected, single, multiple), and provides step-by-step dilution protocols for multi-well formats. Log-space arithmetic prevents overflow for high-MOI systems (e.g., AAV at 100,000 vg/cell).
Last validated 2026-03-19. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience MOI / Infection Planning Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/moi-calculator
Multiplicity of infection (MOI) is the ratio of infectious agents (e.g., virus particles) to infection targets (e.g., cells). It is the single most important parameter in any transduction, infection, or gene delivery experiment.
At MOI = 1, each cell gets an average of one virus particle. However, because particles distribute randomly, the actual number per cell varies. The Poisson distribution describes this: at MOI = 1, about 36.8% of cells receive zero particles, 36.8% receive exactly one, 18.4% receive two, and 6.1% receive three.
The probability that a cell receives exactly k virus particles at a given MOI follows the Poisson distribution:
This model assumes three things: (1) virus particles are uniformly mixed, (2) each particle has an equal probability of infecting any cell, and (3) particles behave independently. These assumptions hold well in suspension culture with thorough mixing.
In practice, the Poisson model slightly overestimates the uninfected fraction because it assumes ideal mixing. Cell aggregation, surface attachment, and receptor saturation can all cause deviations. Despite this, the Poisson model remains the standard for experiment planning because it provides a reliable conservative estimate.
Always determine your virus titer experimentally before starting large-scale experiments. Vendor-supplied titers are measured on specific cell lines (often HEK293T) and may not reflect performance on your target cells.
Freeze-thaw cycles reduce lentivirus titer by approximately 50% per cycle. Aliquot virus stocks into single-use volumes immediately after production. Store at -80°C.
For lentiviral transduction, polybrene (hexadimethrine bromide) at 4–8 µg/mL enhances transduction by neutralizing charge repulsion between viral and cell membranes. Some cell types (especially hematopoietic cells) are sensitive to polybrene — test toxicity first or use protamine sulfate as an alternative.
