DNA Copy Number Calculator
Convert nucleic-acid concentration and length into molecule copies, with an optional idealized PCR projection.
On this page
CalculatorHow to useFormula & methodWorked exampleCounting molecules from massWhich length belongs in the calculation?PCR projection is an idealizationFrequently asked questionsRelated calculatorsSourcesHow to use this calculator
- Choose the nucleic-acid type and enter template length.
- Enter concentration and the volume represented by the desired copy count.
- Leave PCR cycles at zero for the original sample, or enter cycles and efficiency for a theoretical amplification estimate.
Formula and method
For the assumptions behind these results, read the explanation below. You can also explore DNA Concentration and Ligation.
A worked example
Ten nanograms of 1,000 bp double-stranded DNA contains approximately 9.12 billion molecules. With zero PCR cycles, the projected count is the same as the starting count.
Counting molecules from mass
A balance or concentration measurement gives the mass of nucleic acid, while many experiments need an approximate number of template molecules. Molecular weight connects those two quantities. Dividing grams by grams per mole gives moles; multiplying by Avogadro’s constant gives molecules.
For a duplex template, length is entered in base pairs. For a single strand, it is entered in nucleotides. The selected average mass per unit length is an approximation and does not include every sequence-specific or chemical modification effect.
Which length belongs in the calculation?
Use the length of the molecule whose mass concentration was measured. If the preparation contains a plasmid carrying a short insert, the full plasmid length is needed to count plasmid molecules from total plasmid mass. Using only the insert length would overestimate their number.
Copies per microliter is a concentration; copies in the sample is a total. Doubling the sampled volume doubles total copies while leaving concentration unchanged. A mixture of several templates cannot generally be assigned a single exact molecule count from one average length.
PCR projection is an idealization
An efficiency of 100% doubles the number each cycle. An efficiency of 90% multiplies it by 1.9. The projection assumes the same efficiency at every cycle and ignores reagent depletion, inhibition, and plateau effects.
For RNA, the mass-to-copy calculation still applies. A PCR projection involving RNA additionally assumes an appropriate conversion to amplifiable template; this calculator does not model reverse-transcription yield.
Frequently asked questions
What is the Avogadro constant?
It is exactly 6.02214076 × 10²³ entities per mole in the SI system.
Why does longer DNA give fewer copies for the same mass?
Each longer molecule weighs more, so fewer molecules are needed to make up a fixed mass.
Is a very large projected copy number experimentally achievable?
Not necessarily. Exponential arithmetic ignores the practical limits of an actual reaction.
Sources and further reading
- NIH PubMed Central — NIST Study of DNA Concentration Measurement ↗
Discusses conversion between DNA mass and copy measurements using an approximate 660 g/mol per base pair, with measurement limitations.
- Michigan State University Teaching Archive — DNA Replication and RNA Transcription ↗
Gives approximate DNA molecular masses of 330 daltons per nucleotide and 660 daltons per base pair.
- NIH PubMed Central — Quantification of Bacterial RNA Targets in Water ↗
Reports average masses of 660 g/mol per DNA base pair and 340 g/mol per RNA nucleotide, and defines 100% PCR efficiency as doubling each cycle.
- National Institute of Standards and Technology — SI conversion factors ↗
Reference for physical unit conversions. The calculator converts measurements before applying its formula.
Our explanations are written for BiologyCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.