PCR master-mix volume calculations
A PCR master mix combines shared reaction components to improve consistency across tubes or wells. For each concentration-defined reagent, the required per-reaction volume follows C₁V₁ = C₂V₂.
The included default rows are an arithmetic example, not a universal PCR formulation. Reagent concentrations, units, component inclusion, reaction volume, controls, and cycling conditions must come from a validated assay or manufacturer protocol.
How to use the PCR master mix calculator
- Start from a validated recipe: Replace example rows with the exact reagent stocks, targets, and units from the governing protocol.
- Mark included components: Select components prepared in the shared master mix and leave sample-specific components excluded.
- Set reaction count and overage: Include all samples and required controls, then use the protocol-appropriate pipetting overage.
- Calculate and verify: Confirm component volumes plus water equal the final volume and every transfer is practical.
Formula and variables
Stock and final concentrations must use compatible units within each row. Water fills the remaining final reaction volume.
V₁ = C₂V₂/C₁; total included volume = V₁ × reactions × (1 + overage/100)- C₁ — Stock concentration
- Concentration of the reagent stock (row-specific)
- V₁ — Reagent volume
- Volume added per reaction (µL)
- C₂ — Final concentration
- Target concentration in the completed reaction (compatible with C₁)
- V₂ — Reaction volume
- Total volume of one reaction (µL)
Scale a validated ten-reaction setup
Prepare ten 50 µL reactions with 10% overage while adding a 1 µL template separately.
- Reaction equivalents
- 11
- Template
- 1 µL per reaction, excluded
- Final volume
- 50 µL
- Each included reagent volume = C₂ × 50/C₁
- Included totals and water are multiplied by 11
Result: The table reports per-reaction volumes and the shared master-mix total.
Excluded template is added separately and is not multiplied into the shared mix total.
Understanding your results
Volume arithmetic does not validate an assay
A mathematically balanced recipe can still fail if reagent identities, units, concentrations, handling, controls, or cycling parameters are wrong.
- Stock and final units must be compatible within each row.
- Overage applies only to included master-mix components and water.
- Excluded components remain listed per reaction.
- Controls must be counted in the reaction total.
Assumptions
- Each row follows a linear concentration dilution relationship.
- Volumes are additive at the required precision.
- The entered PCR formulation has already been validated for the intended assay.
Limitations
- Does not design primers, optimize Mg²⁺ or annealing conditions, select enzymes, or validate reagent compatibility.
- Does not enforce manufacturer-specific formulation limits or contamination-control workflow.
- Does not calculate replicate design, standard curves, PCR efficiency, or uncertainty.
Common mistakes
- Using incompatible units in a stock/final pair.
- Forgetting controls in the reaction count.
- Including sample-specific template in a shared mix.
- Treating the example defaults as a recommended assay formulation.
Practical use cases
Validated assay scaling
Scale shared reagent volumes for samples and controls while allowing pipetting overage.
PCR arithmetic education
Explore how stock concentration determines volume per reaction.
Frequently asked questions
Should template be included in the master mix?
Often it is sample-specific and added separately, but follow the exact assay protocol. The table lets you choose per component.
Why add overage?
A protocol may specify extra reaction equivalents to account for pipetting losses; use its stated amount rather than assuming one percentage fits every setup.
Can I mix mM stock with µM final values?
Convert them to compatible units before entry because the calculator treats the two numeric concentration fields as the same unit scale.
Sources and review
- Luna Universal qPCR Master Mix Protocol — New England Biolabs. Accessed 2026-07-13.
- MIQE guidelines — Clinical Chemistry via PubMed. Accessed 2026-07-13.
Reviewed 2026-07-13.