DNA Copy Number Calculator

The DNA Copy Number Calculator converts between nucleic acid concentration and the number of DNA or RNA molecule copies in a sample — a common need when preparing standards for qPCR, ddPCR, or cloning workflows. Select your calculation mode (Concentration → Copy Number or vice versa), choose your DNA/RNA type (dsDNA, ssDNA, or RNA), then enter your fragment length, concentration, and volume to get copy number per µL, total copies in the sample, molecular weight, molarity, and mass per copy.

Calculation Mode *

bp

Length in base pairs (bp) for DNA or bases for RNA

ng/µL
µL
copies/µL
g/mol

Override calculated molecular weight if known

Results

Copy Number

--

Total Copies in Volume

--

Molecular Weight

--

Molarity

--

Mass per Copy

--

More Biology Tools

Frequently Asked Questions

How is copy number calculated?

Copy number is calculated using the formula: copies/µL = (concentration × Avogadro's number) / (fragment length × molecular weight per bp). First, we determine the molecular weight based on DNA/RNA type and length, then convert mass to moles, and finally to molecules using Avogadro's constant (6.022 × 10²³).

What's the difference between dsDNA and ssDNA calculations?

Double-stranded DNA (dsDNA) has approximately 660 g/mol per base pair, while single-stranded DNA (ssDNA) has about 330 g/mol per base. RNA is slightly heavier at 340 g/mol per base due to the extra hydroxyl group. This difference affects the molecular weight calculation and final copy number.

How many copies are needed for PCR amplification?

For reliable PCR amplification, you typically need at least 1-10 copies of your target sequence per reaction. However, 100-1000 copies per reaction often provide better consistency and stronger signals. The exact number depends on your PCR efficiency and detection method.

Can I use this calculator for plasmids?

Yes, treat plasmids as double-stranded DNA (dsDNA) and enter the total plasmid length in base pairs. For circular plasmids, use the complete sequence length. This calculator works for any DNA fragment including genomic DNA, PCR products, and plasmids.

Why do I need to know the fragment length?

Fragment length is essential because molecular weight scales directly with the number of base pairs or bases. A 100 bp fragment has 1/10th the molecular weight of a 1000 bp fragment, resulting in 10 times more copies for the same mass concentration.

What if my molecular weight is different from the standard values?

You can enter a custom molecular weight in the advanced options if you know the exact value. This is useful for modified nucleotides, labeled DNA, or when you have precise mass spectrometry data. The calculator will use your custom value instead of the estimated weight.

How accurate are these calculations?

The calculations are highly accurate for the molecular weight estimates used (660 g/mol per bp for dsDNA, 330 g/mol for ssDNA, 340 g/mol for RNA). Real-world accuracy depends on the precision of your concentration measurement and the actual base composition of your specific sequence.