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PCR Reaction Sample Capacity Estimator

The PCR Reaction Sample Capacity Estimator calculates how many complete PCR reactions can be set up from an available sample or template volume. It divides usable sample volume by the amount required per reaction and can reserve a specified dead or holdback volume before calculating capacity.

This is useful when sample is limiting and you need to estimate the maximum number of reactions, replicates, or assays that can be supported without planning to consume every microliter. The result uses whole reactions only; any remainder is shown separately.

Inputs

µL
µL
µL
Result
—
Complete reactions
Usable sample volume—
Volume used for complete reactions—
Remaining usable volume—

1. Enter available sample
Use the measured volume currently available for PCR setup.

2. Reserve inaccessible or protected volume
Enter any volume you want to hold back or expect cannot be reliably aspirated.

3. Enter sample volume per reaction
Use the template/sample volume specified for one reaction in your protocol.

4. Review whole-reaction capacity
The main result rounds down because a partial reaction is not counted as complete.

5. Check the remainder
Use the remaining-volume line to see how much usable sample is left after the maximum complete-reaction count.

Usable sample volume = Available volume − Reserved volume Complete reactions = floor(Usable sample volume ÷ Sample volume per reaction) Remaining usable volume = Usable sample volume − Complete reactions × Sample volume per reaction

Where:

  • Available volume — total measured sample/template volume
  • Reserved volume — volume deliberately held back or treated as inaccessible
  • Sample volume per reaction — sample/template volume consumed by one reaction
  • floor — rounding down to the nearest whole reaction

Assumptions: The calculation considers volume only. It does not determine whether concentration, quality, biological replicates, or assay design are sufficient.

What the result means

After reserving 10 µL, the remaining 110 µL can support twenty-two reactions at 5 µL per reaction.

Sample capacity is based on volume only and always rounds down to complete reactions.

Given:

  • Available sample = 120 µL
  • Reserved volume = 10 µL
  • Sample per reaction = 5 µL

Calculation:
Usable volume = 120 − 10 = 110 µL
Complete reactions = floor(110 ÷ 5) = 22
Remaining usable volume = 110 − 22 × 5 = 0 µL

Result:
22 complete reactions

Interpretation:
After reserving 10 µL, the remaining 110 µL can support twenty-two reactions at 5 µL per reaction.

Why does the calculator round down?

A reaction that lacks the full required sample volume is not counted as complete. Rounding down prevents the capacity estimate from assuming a fractional reaction can be run.

What should I use for reserved volume?

Use a value consistent with your tube, pipette, sample handling plan, and laboratory procedure. It can represent dead volume, a retention aliquot, or any amount you do not want consumed.

Does this account for pipetting overage?

Not separately. If you expect sample loss during transfers, include that amount in the reserved volume or use a more conservative available volume.

Can I plan technical replicates with this result?

Yes. Divide the complete-reaction capacity by the number of replicates required per sample or condition, while also reserving capacity for controls as needed.

Does enough volume mean the sample is suitable?

No. Volume capacity does not assess nucleic-acid concentration, purity, inhibition, integrity, or assay-specific acceptance criteria.