MOI Calculator
Calculate the virus volume needed for infection and transduction experiments using cell number, desired multiplicity of infection (MOI), and viral titer. This MOI calculator helps scientists estimate virus stock volume, preparation volume, and media requirements for lentiviral, AAV, adenoviral, and general viral workflows.
MOI Calculator
Results
Lab Summary Card
Formula and Calculation Logic
Multiplicity of infection, or MOI, describes the intended number of viral units added per cell. The biological meaning depends on how the viral titer was measured, so an MOI based on infectious units is not the same as an MOI based on physical particles.
Titer units should be interpreted carefully. TU/mL usually refers to transducing units per mL, IFU/mL to infectious units per mL, PFU/mL to plaque-forming units per mL, VG/mL to vector genomes per mL, and particles/mL to physical particle counts. VG/mL and particles/mL may not represent infectious activity directly.
Use the estimated cell number at the time of infection or transduction, not only the original seeding density. This matters especially 24-72 hours after plating, when cell growth can substantially change the actual number of target cells.
Example Workflow
A scientist is planning a lentiviral transduction experiment in a multiwell plate and needs to prepare enough infection mix for all wells while accounting for overage and the estimated number of cells at the time of transduction.
Enter cell number, wells/samples, MOI, titer, titer unit, and final infection/transduction volume.
Review the total virus stock, media/diluent, and total mix volume needed for the experiment.
Prepare the mix, dispense consistently across wells, and document MOI, titer unit, cell estimate, virus lot, and exposure conditions in the ELN.
Common Mistakes
Estimate the cell number at dosing time, especially after growth overnight or over multiple days. A Cell Doubling Time Calculator or Cell Growth Kinetics Calculator can help estimate the cell count when direct counting is not practical.
Over-confluent cultures can alter receptor availability, cell-cycle state, uptake, viability, and transduction or infection efficiency.
Vector genomes and particle counts may not equal infectious or transducing units. Confirm whether the titer reflects functional activity in a relevant assay.
Prepare extra mix to account for pipette tips, reservoirs, tube hold-up, and small losses during dispensing.
When calculated virus volumes are very small, prepare a working dilution to improve pipetting accuracy and consistency across wells.
The same nominal MOI can produce different biological responses depending on cell type, receptor expression, growth state, and vector system.
High MOI can increase toxicity, innate immune activation, multiple integration events, or assay interference depending on the system.
Record the titer method, virus lot, cell passage, storage conditions, and freeze-thaw history so results can be interpreted and repeated.
Frequently Asked Questions
What is an MOI calculator used for?
An MOI calculator estimates how much virus stock and media or diluent to prepare for infection or transduction experiments based on cell number, desired MOI, viral titer, sample count, and final volume.
How do I calculate virus volume from MOI?
Multiply the number of cells by the desired MOI to get viral units needed, then divide by the viral titer. The calculator scales that volume across samples and applies overage for practical preparation.
What is the difference between TU/mL, IFU/mL, PFU/mL, VG/mL, and particles/mL?
TU/mL, IFU/mL, and PFU/mL are commonly used for functional or infectious measurements. VG/mL and particles/mL describe physical vector genomes or particles and may not directly equal infectious activity.
What MOI should I use for lentiviral transduction?
The best MOI depends on cell type, vector design, promoter, expression goal, toxicity, and selection strategy. Many workflows test a small MOI range before choosing final conditions.
Can I use seeding density to calculate MOI?
Use seeding density only if it closely matches the cell number at infection or transduction. If cells have grown for 24-72 hours, estimate or measure the actual cell number before calculating MOI.
Why does the same MOI behave differently across cell types?
Cell permissiveness, receptor expression, cell-cycle state, growth rate, innate responses, and culture conditions can all change apparent infection or transduction efficiency at the same nominal MOI.
Should I include overage when preparing viral transduction mixtures?
Yes. Overage helps cover pipetting losses, dead volume in tubes or reservoirs, and small dispensing differences across wells or samples.
Why is my calculated virus volume too small to pipette accurately?
Very high-titer virus stocks can produce sub-microliter or low-microliter volumes. In that case, prepare a working dilution and add a larger, more accurate volume to each sample.