qPCR Master Mix Calculator with Overage and Dead Volume
Prepare a reaction master mix with explicit percentage overage and a fixed dead-volume allowance. The reference keeps template additions separate from the shared mix and calculates component volumes from their stock and final concentrations. It is a volume-planning example, not a validation of a primer/probe assay or a multi-target reaction chemistry.
Existing independently checked volume example based on the recorded TaqMan Fast Advanced setup: 20 µL reactions, 2× master mix, 20× assay, water and separately added template. It uses sixteen reactions rather than silently relabelling the source as a triplicate design.
Define what is shared across reactions
A master mix contains components that are identical across the reactions receiving it. Sample template, target-specific primer/probe sets or other varying additions may need to remain separate. Start by grouping reactions according to actual composition, then count the wells in each group. This avoids preparing one apparently convenient mix that does not match the intended experiment.
The final reaction volume includes both the dispensed mix and separate additions. Water fills the remaining volume only after all required components are accounted for. If the requested component volumes exceed the final volume, the correct result is a refusal or correction request, not a negative water volume hidden in an export. Review concentration units as well as the numerical amounts.
Relate allowances to dispensing practice
A percentage allowance covers proportional preparation and dispensing uncertainty, while fixed dead volume can represent a reservoir or transfer device. Neither is a universal constant. The reference supplies both to demonstrate the calculation. Change them to reflect the actual vessel and dispensing method, and check whether the smallest component volume is practical to pipette reproducibly.
Keep the prepared mix identity and reaction layout with the experiment. A correct volume table does not establish that primers match the template or that amplification is efficient. Use the primer-inspection workflow for a different question about sequence and melting-temperature assumptions, and preserve qPCR measurement controls for the eventual expression analysis. Preparation arithmetic and assay performance should remain separately documented.
Equations and variables
Per-reaction stock volume
Vi = (ctarget,i/cstock,i) × Vreaction
- Vi
- Volume of stock component i per reaction (µL)
- ctarget,i, cstock,i
- Compatible target and stock concentrations
- Vreaction
- Final reaction volume (µL)
Shared-mix batch volume
Vbatch = N × Vmix × (1 + o/100) + Vdead
- N
- Number of reactions receiving the shared mix
- Vmix
- Shared mix volume per reaction, excluding separate additions (µL)
- o
- Percentage overage
- Vdead
- Fixed unrecoverable-volume allowance (µL)
Scope and limitations
- Overage and dead volume represent different allowances and should not be counted twice for the same loss.
- Target-specific reagents may require separate mixes. Combining all targets into one volume table does not establish compatible multiplex chemistry.
- The calculation assumes homogeneous mixing and accurate stocks. It does not assess inhibition, amplification efficiency, contamination or assay specificity.
Sources and provenance
- Calculator inputs and independent arithmetic verificationOriginal synthetic inputs; see individual fixture notices
- Independent master-mix cases and recorded source protocolOriginal arithmetic reference; protocol source cited within fixture
Technical questions
Is ten percent overage the same as twenty-five microlitres dead volume?
No. Percentage overage scales with the nominal batch size, whereas dead volume is a fixed allowance for material that cannot be dispensed. They can both be appropriate, but their practical meanings should be documented so the same handling loss is not covered twice without intention.
Why is template added separately?
Different reactions often receive different samples or water for a no-template control. Including all templates in one common mix would remove those distinctions. The example therefore reserves the template volume in each final reaction while keeping it outside the shared batch.
How do I plan multiple targets in triplicate?
Calculate the actual reaction count for each distinct mix, including controls, and retain the target/sample layout separately. A count can reflect triplicates, but the calculator does not infer that design from the number alone or validate a multiplex assay simply because its volumes sum correctly.
Connected workflows
- Primer-pair Tm and template matching
Inspect primer sequence and thermodynamic assumptions separately from reagent volumes.
- 96-well dose-response plate mapping
Record the reaction layout and control roles.
- 4PL standard-curve interpolation
Compare another workflow where standards and unknown samples must remain distinct.
- qPCR Delta-Delta Cq and Pfaffl Fold Change Calculator
After setting up the reactions, analyse the resulting Cq values as relative expression.
- PCR Reaction Master Mix Planner for 2x Polymerase Mixes
Plan an endpoint PCR batch with a 2x reagent, primer stocks and a dead volume.