🧬 PCR Master Mix Calculator
Scale up per-reaction PCR component volumes to a master mix for multiple reactions, with built-in pipetting overage.
| Component | Per Reaction | Total Needed |
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Frequently asked questions
How much overage should I add?
10% overage is a common default, covering roughly 1 extra reaction per 10 samples. For larger batches (48+ reactions) or when pipetting very small volumes, 5% may be sufficient; for small batches or less experienced pipetting, up to 15-20% overage provides a safer margin.
Should template DNA be included in the master mix?
Typically no — template DNA is usually added separately to each individual reaction tube after the master mix (containing everything else) has been aliquoted, to avoid cross-contamination between samples. This calculator includes template as an optional line so you can see its contribution to total reaction volume, but you may choose to prepare it separately.
What if my water volume calculates as zero or negative?
Zero means your other components already sum to exactly your total reaction volume (no dilution water needed). A negative result means your entered component volumes exceed the total reaction volume — double check that your master mix, primer, and template volumes are entered correctly relative to your intended total reaction size.
Accuracy & how this is derived
Derivation: Direct linear scaling: each component's total volume equals its per-reaction volume multiplied by the number of reactions and an overage factor (1 + overage%) to account for pipetting loss. Water volume is calculated as the remainder needed to reach the specified total reaction volume.
Validated against: Standard PCR master mix preparation approach described in molecular biology laboratory manuals (e.g. Sambrook & Russell, Molecular Cloning) and PCR reagent manufacturer protocols.
⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.
✔ Last updated: July 2026 · Report an error
Scaling up PCR reactions with a master mix
Preparing a PCR master mix means combining all reaction components common to every sample — buffer, polymerase, dNTPs, and primers — into a single bulk mixture that is then aliquoted across all reaction tubes, reducing pipetting error and ensuring consistency between replicates. Scaling the per-reaction recipe up to the correct total volume requires multiplying each component by both the number of reactions needed and a small overage factor to account for the small but unavoidable volume loss that occurs during pipetting and mixing.