Calculate how many double-stranded DNA molecules are in a sample from mass in nanograms and length in base pairs.
| Copies | – |
Use this calculator when a protocol asks for copy number (qPCR standards, transfection, genome equivalents) and you only know the mass of a plasmid, amplicon, or fragment.
Copies = mass in ng × Avogadro's number ÷ (length in base pairs × 10⁹ × 650). The 650 daltons per base pair is the usual average molecular mass of a dsDNA base pair; 10⁹ converts nanograms to grams. Use the length of the molecule you actually weighed, including the backbone of a plasmid.
This is a theoretical count of intact dsDNA molecules. It does not account for nicked DNA, impurities, or single-stranded material.
Mass (ng): How much dsDNA you have, in nanograms.
Length (bp): Length of that molecule in base pairs (plasmid, insert, or genome fragment).
Copies: Estimated number of dsDNA molecules.
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