What is DNA copy number?
In molecular biology, the DNA copy number (or simply number of copies) refers to the absolute number of DNA molecules present in a specific sample or reaction. Accurately determining copy number is absolutely crucial for quantitative techniques like Real-Time PCR (qPCR), digital droplet PCR (ddPCR), and when quantifying plasmid standards.
Formula for calculating copy number
To calculate the number of double-stranded DNA molecules from its mass, we rely on Avogadro's constant and the average weight of a single DNA base pair. The generalized formula is:
Number of Copies = (Mass × 6.022 × 10²³) / (Length × 660)
- Mass: The mass of your DNA, standardized to grams (g)
- 6.022 × 10²³: Avogadro's Number (molecules/mole)
- Length: The length of your DNA template in base pairs (bp)
- 660: The average molecular weight of a single DNA base pair (g/mol/bp)
How to use this calculator
Calculating the exact molecular copy number in your tube is incredibly easy:
- Enter the measured Mass of your DNA sample.
- Select the correct unit for mass (ng, µg, or mg).
- Enter the total Length of the DNA fragment or plasmid.
- Select the unit for length (bp, kb, or Mb).
- The calculator will instantly display the absolute total number of DNA molecules.