MOI Calculator

MOI is the ratio of infectious units added to the number of target cells: MOI = infectious_units_added / cells.

With a stock titer expressed as infectious units per mL: infectious_units_added = titer_per_mL × virus_volume_mL.

Solving for virus volume for a target MOI: virus_volume_mL = (target_MOI × cells) / titer_per_mL. The tool also reports how much media to add to reach your chosen infection volume.

1. Pick a mode: target planning or back-calculation.
2. Enter cells, stock titer, and infection volume per replicate.
3. Optional: set replicates and add overage for pipetting.
4. Press Submit. Results show above the form and are saved.
5. Export CSV or PDF for your notebook records.

Operational context for MOI planning

Multiplicity of infection (MOI) links infectious units added to the number of target cells. In routine culture infections, MOI often ranges from 0.01 to 10, depending on assay goals, entry efficiency, and cytotoxicity. This calculator standardizes inputs so teams can reproduce exposure conditions across plates, days, and operators.

Input data quality and titer handling

Titer is frequently reported as infectious units per milliliter from plaque, focus-forming, or TCID50-derived estimates. A one-log titer shift changes required virus volume tenfold at fixed MOI and cell number. For example, 1×10⁶ cells at MOI 0.1 needs 1×10⁵ infectious units; that is 1.0 µL at 1×10⁸/mL, but 10.0 µL at 1×10⁷/mL.

Volume constraints and pipetting precision

Very small calculated volumes can fall below reliable pipetting limits. When virus volume is under 2 µL, an intermediate dilution (for instance 1:10 or 1:100) improves accuracy and reduces variance. The optional overage setting (commonly 5–10%) compensates for dead volume and transfer loss when preparing master mixes for multiple replicates.

Replicates, scaling, and master mix strategy

Scaling totals is essential for multiwell workflows. If a protocol uses 0.5 mL infection volume and eight replicates, the calculator reports total mix volume (4.0 mL) and splits it into total virus and total media. This supports batch preparation, consistent timing, and fewer handling errors, especially during synchronized infections.

Interpreting results and expected exposure

MOI is a planning ratio, not a guarantee that each cell is infected. Infection outcomes follow probabilistic exposure and biological constraints. In many models, the fraction of uninfected cells decreases as MOI increases, but receptor availability, cell cycle state, and aggregation can shift effective exposure. Use controls to validate actual infection rates.

Documentation, traceability, and reporting

The session history table, CSV export, and PDF summary help document inputs, outputs, and notes alongside experimental metadata. Recording cells, titer, infection volume, and calculated virus volume improves traceability during troubleshooting. Standardized reporting also helps compare conditions across cell lines, viral stocks, and batches. For audits, include stock identifier, passage, assay date, and dilution scheme; these fields make recalculation and replication straightforward across collaborators and reviewers.

1) What does MOI represent in practice?

MOI is the planned ratio of infectious units added per target cell. It standardizes dosing but does not guarantee uniform infection because biology and mixing affect effective exposure.

2) Why can two experiments at the same MOI show different infection rates?

Differences in cell health, receptor density, clumping, adsorption time, temperature, and titer measurement method can change effective entry, even when calculated MOI is identical.

3) When should I use an intermediate dilution?

Use it when the calculated virus volume is very small (often under 2 µL) or when pipetting accuracy is critical. Dilutions improve precision and reduce run-to-run variability.

4) Which titer should I enter: genome copies or infectious units?

Enter infectious units (plaque, focus-forming, or TCID50-based) because MOI is defined by infectious particles. Genome copy measurements can overestimate functional infectivity.

5) What does the overage setting change?

Overage increases the calculated virus volume and media volume proportionally to reduce shortages caused by dead volume, evaporation, or transfer loss when preparing a master mix.

6) Can I use this for bacteria-phage or viral vectors?

Yes, as long as your “titer” is in infectious units per volume and the target count reflects susceptible hosts. Always validate the assay-specific definition of infectious units.