🔢 DNA Copy Number Calculator
Translate DNA mass or concentration into absolute molecule counts for cloning, qPCR, and sequencing workflows.
Provide mass directly, or specify concentration and volume below.
How to Use This Calculator
Provide fragment length
Enter the size of your amplicon, plasmid, or fragment in base pairs. This determines the molecular weight used in calculations.
Enter mass or concentration
Input DNA mass in nanograms, or supply concentration and volume to derive total mass automatically.
Review copy number output
Run the calculation to see total copies and, when concentration and volume are provided, copies per microliter.
Formula
copies = (mass (ng) × 10-9 g/ng) × NA ÷ (length (bp) × 660 g/mol)
Where NA is Avogadro's number (6.022 × 1023). The factor 660 g/mol is an average molecular weight per base pair for double-stranded DNA.
To find copies per microliter, divide the copy number by the reaction volume in µL.
Full Description
Converting mass to absolute copy number is essential for qPCR standard curves, viral load quantification, and precise plasmid titrations. Because mass measurements often rely on spectrophotometry or fluorimetry, translating those values into molecule counts provides a universal reference regardless of fragment size.
This calculator assumes double-stranded DNA and uses a standard molecular weight conversion. Sequence composition can cause minor variation, but the approximation is sufficient for most laboratory planning tasks.
Frequently Asked Questions
Do I need both mass and concentration?
No. Provide either the total mass directly or a concentration with its volume. The calculator determines mass from whichever data you supply.
Can I use this for single-stranded DNA or RNA?
The 660 g/mol factor applies to double-stranded DNA. For ssDNA or RNA, use 330 g/mol per nucleotide to improve accuracy.
How accurate is the copy number estimate?
Accuracy depends on the precision of your mass or concentration measurements and the assumption of average molecular weight. For critical applications, verify with standards or digital PCR.
What if my volume is in milliliters?
Convert the volume to microliters before entering it. Multiplying mL by 1000 yields µL, ensuring the copies per µL value is correct.