How this calculator works
Molecule count is sample mass divided by approximate molar mass, multiplied by the exact Avogadro constant. Average masses of 660 g/mol per double-stranded DNA base pair, 330 per single-stranded DNA base and 340 per RNA base are rough composition-independent conventions. Sequence-specific molar mass is more accurate for short oligonucleotides. PCR extrapolation assumes a constant per-cycle efficiency and no plateau; it is an idealized yield, not measured amplification.
Formula
Copies = mass (g) × 6.02214076 × 10^23/[length × average base molar mass (g/mol)]. After PCR: final = initial × (1 + efficiency)^cycles. At 100% efficiency the factor is two.
Worked example
A 1000 bp double-stranded template has an approximate molar mass of 660000 g/mol. A 660 ng sample contains 6.02214076 × 10^11 copies. Starting with 100 copies and three ideal doubling cycles gives 800 copies.
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Frequently asked questions
Do I enter the whole plasmid length?
Yes. Use the length of the complete molecule whose copies you count, not just the insert or amplified target.
Is concentration enough to calculate total copies?
Total copies also need an aliquot volume. With a 1 uL aliquot the result is numerically copies per uL.
Why might the PCR prediction be too high?
Efficiency may fall during amplification and reactions eventually plateau. The constant-efficiency model cannot capture those limits.