DNA Copy Number Calculator

Determine the number of DNA or RNA copies in a solution and per PCR cycle

You can edit any field to solve for the remaining one using bidirectional LRU calculation.

Last updated: December 31, 2025

CreatorFrank Zhao

DNA concentration

More info

ng/µl

Template length

More info

Base weight

DNA copies

More info

× 10⁷

copies/µl

Initial DNA copies

More info

× 10⁷

copies/µl

Number of PCR cycles

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DNA copies after PCR cycle(s)

More info

× 10⁷

copies/µl

1DNA copies

N = \frac{6.02214\times 10^{14}\,c}{w\,L}

Where

c

is DNA concentration (ng/µl),

L

is template length (bp), and

w

is base weight (Da).

2DNA copies per PCR cycle

P = I\cdot 2^{n}

NDNA copies

cDNA concentration

LTemplate length

wBase weight

IInitial DNA copies

nPCR cycles

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Welcome to the DNA copy number calculator

This calculator converts a DNA/RNA mass concentration (in ng/µL) into an estimated copy number per microliter, and it also works in reverse if you start from a target copy number.

Practical use: it helps you set up PCR reactions, plan dilutions, and sanity-check whether your template input is in a reasonable range.

Who is this for?

Molecular biology workflows (PCR, cloning, qPCR setup)
Sequencing prep when you need comparable template input
Any time you need copies/µL instead of ng/µL

Why the calculator is reliable

The copy-number conversion is based on Avogadro-scale counting and a molecular weight estimate per base (or base pair). Internally, the calculator keeps a high-precision “base state” so shared links reproduce the same result.

If you also need to measure the concentration first, our DNA Concentration Calculator pairs nicely with this one.

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Formula for the DNA/RNA copy number

The idea is straightforward: if you know the mass of nucleic acid in $\mathrm{ng/\mu L}$ , you can estimate how many molecules that corresponds to by dividing by the mass per molecule.

Core formula used by the calculator

N = \frac{6.02214\times 10^{14}\,c}{w\,L}

Here $N$ is copies per microliter, $c$ is DNA concentration in $\mathrm{ng/\mu L}$ , $L$ is the template length in base pairs, and $w$ is the average base (or base-pair) weight in daltons.

Where the constant comes from

The factor $6.02214\times 10^{14}$ is a convenient combination of Avogadro’s constant $N_A\approx 6.02214\times 10^{23}$ and the nanogram conversion $10^{9}$ .

ssDNA

Average base weight: $w = 330\ \mathrm{Da}$

ssRNA

Average base weight: $w = 340\ \mathrm{Da}$

dsDNA

Average base pair weight: $w = 660\ \mathrm{Da}$

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How to use the DNA copy number calculator (with examples)

You can treat this tool like a two-way converter: fill any two fields and the third becomes the blue “result” field. If you overwrite the blue field, the calculator will switch which variable is solved for.

Enter your DNA concentration

Use your measured value in $\mathrm{ng/\mu L}$ .

Set template length

Enter the total template length $L$ (bp). Whole genomes can be millions of base pairs; plasmids are often a few thousand.

Choose base weight (ssDNA/ssRNA/dsDNA)

Pick the option that matches your nucleic acid. This matters because the mass per base (or base pair) changes.

Read (or edit) the copy number result

The blue field is the variable currently being solved for.

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Pro tip:

If you want to share your current inputs and results, click the Share button and enable the option to share results. The generated link preserves values and collapsed-section states.

Example: convert ng/µL to copies/µL

Suppose you measured $c = 150\ \mathrm{ng/\mu L}$ , your template is $L = 4{,}700{,}000\ \mathrm{bp}$ , and you select dsDNA $w = 660\ \mathrm{Da}$ .

N = \frac{6.02214\times 10^{14}\,c}{w\,L}

=

\frac{6.02214\times 10^{14}\times 150}{660\times 4{,}700{,}000}

\approx

2.91\times 10^{7}\ \mathrm{copies/\mu L}

Interpretation: in every microliter of that stock, you have about $2.91\times 10^{7}$ genome copies.

Example: prepare a dilution from a stock

Let your stock be $C_{stock} = 2.91\times 10^{7}\ \mathrm{copies/\mu L}$ . You want $C_{target} = 2.0\times 10^{6}\ \mathrm{copies/\mu L}$ in a total volume of $V_{total} = 10\ \mathrm{\mu L}$ .

V_{stock} = \frac{C_{target}}{C_{stock}}\,V_{total}

=

\frac{2.0\times 10^{6}}{2.91\times 10^{7}}\times 10

\approx

0.69\ \mathrm{\mu L}

So you would mix about $0.69\ \mathrm{\mu L}$ of stock with $9.31\ \mathrm{\mu L}$ of water/buffer.

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Formula for the gene copy number per PCR cycle

In the idealized case, PCR doubles the number of molecules every cycle. That gives an exponential relationship between the starting copies and the copies after $n$ cycles.

PCR growth model

P = I\cdot 2^{n}

$I$ is the initial copies per µL, $n$ is the number of cycles, and $P$ is the copies per µL after $n$ cycles.

Example: copies after 10 cycles

If $I = 1.4\times 10^{5}$ copies/µL and $n = 10$ :

P = 1.4\times 10^{5}\cdot 2^{10}

=

1.4\times 10^{5}\cdot 1024

\approx

1.4336\times 10^{8}\ \mathrm{copies/\mu L}

In practice, efficiencies below $2$ per cycle are common, and amplification may plateau.

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Real-world examples / use cases

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Genome copy normalization

Convert a measured concentration into copies/µL so different samples feed the same template count into a downstream assay.

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PCR cycle planning

Estimate how many cycles you might need to reach a target copy number (ideal doubling assumption).

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Plasmid / amplicon prep

For short templates, copy number rises quickly. The template length field is the biggest lever.

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Dilution math for standards

Back-solve what concentration you need, then compute how much stock volume to pipette.

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Primer sanity checks

If PCR behaves oddly, revisit reaction setup. Our Annealing Temperature Calculator can help tune parameters.

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Tips & best practices

Common mistakes to avoid

Using the wrong template length: $L$ should match what you are actually amplifying.
Selecting dsDNA for a single-stranded assay: the base weight $w$ changes the result.
Treating PCR as perfectly exponential forever: in reality, amplification can plateau.

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Accuracy tip:

If your concentration comes from spectrophotometry, impurities can inflate the mass reading. For more robust quantification, consider fluorometric methods in your lab workflow.

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Improving PCR amplification

If your PCR results look weak or messy, the copy-number math may be the easy part — the practical setup matters just as much.

Checklist to improve results

Double-check your kit protocol (enzyme, buffer, Mg²⁺, and cycling parameters).
Verify primer design and specificity. A small temperature shift can matter — use the Annealing Temperature Calculator.
Watch for inhibitors (e.g., heme, urea, some fixatives, carryover salts). Even small contamination can reduce efficiency.
Avoid extremes of template input: too much can increase nonspecific amplification, too little can lead to low yields.

Reminder: the PCR-cycle section assumes ideal doubling. If your system amplifies at a lower efficiency, the real copy number will be lower than $I\cdot 2^{n}$ .

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FAQs

How is copy number calculated?

The calculator uses the following relationship:

N = \frac{6.02214\times 10^{14}\,c}{w\,L}

Make sure units match: $c$ in $\mathrm{ng/\mu L}$ , $L$ in $\mathrm{bp}$ , and $w$ in $\mathrm{Da}$ .

Does each PCR cycle double the copy number?

Ideally, yes: $P = I\cdot 2^{n}$ . In real reactions, efficiency can be below $2$ per cycle and can drop as reagents become limiting.

Why does template length matter so much?

The copy number scales like $1/L$ . If you cut $L$ in half, the estimated copies per µL roughly doubles.

Which base weight should I choose?

Use dsDNA for typical double-stranded templates ( $w = 660\ \mathrm{Da}$ ). Use ssDNA or ssRNA if your assay truly involves single-stranded nucleic acid.

Can I share a link with my exact results?

Yes. Use the Share button and enable sharing with results. The link stores both the displayed fields and the internal high-precision values.

What are copy number variations (CNVs)?

Copy number variation means a genomic segment appears in different copy counts across individuals. It’s a normal source of genetic diversity, and in some contexts it is associated with disease risk.

How many copies after 40 PCR cycles?

Under ideal doubling: $P = I\cdot 2^{40}$ . This number becomes astronomically large, which is a hint that real reactions do not stay exponential for that long.

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Limitations / disclaimers

Limitations to keep in mind

Copy-number conversion uses an average molecular weight per base/base pair. Real sequences vary slightly by composition.
The PCR-cycle model assumes ideal doubling ( $2^{n}$ ). Efficiency can be lower and can drop over time.
This tool is for educational and planning purposes and does not replace protocol-specific guidance.