DNA Copy Number Calculator

How to use the DNA copy number calculator

What this calculator does

This calculator estimates how many DNA or RNA molecules are present in each microliter of a sample when you know the mass concentration and sequence length. It converts nanograms into grams, uses the sequence's approximate molar mass, and multiplies the resulting amount in moles by the exact Avogadro constant. The PCR section then applies an ideal doubling model to show how the calculated starting copy concentration would grow over a selected number of cycles. It is useful for planning dilutions, comparing stocks, estimating template input, and preparing rough assay calculations. It does not measure sample purity, amplification efficiency, primer quality, extraction yield, or biological copy-number variation.

When to use it

Use it when converting a plasmid, amplicon, genomic DNA, single-stranded oligonucleotide, or RNA stock from ng/µL to copies/µL; when checking whether two stocks with different lengths contain comparable molecule counts; when preparing a standard or dilution series; or when exploring the ideal mathematical effect of PCR cycle count. For laboratory decisions, pair the estimate with measured purity, an appropriate assay protocol, and instrument-specific guidance.

How to calculate

1. Enter DNA concentration in ng/µL. Use a positive decimal with a period, such as 150 or 2.5.
2. Enter Template length as a positive whole number. Use base pairs for double-stranded DNA and nucleotides for single-stranded DNA or RNA.
3. Select Molecule type. The calculator uses 660 Da per base pair for dsDNA, 330 Da per nucleotide for ssDNA, or 340 Da per nucleotide for ssRNA.
4. Enter PCR cycles from 0 to 60. Results and the cycle table update live.
5. Read DNA copies, Template molecular mass, PCR fold increase, and Copies after PCR. Review the table for cycle-by-cycle values.
6. Select Download Excel to export the current inputs, outputs, formulas, and projection as a validated workbook. Select Reset to restore the documented defaults.

Input guide

DNA concentration is required, measured in ng/µL, and must be greater than zero. A realistic example is 150 ng/µL. Raising concentration increases copies/µL proportionally. Do not enter a total mass unless it represents the mass in exactly one microliter. Template length is required and must be a whole number from 1 to 1,000,000,000. A bacterial genome might be 4,700,000 bp, while a plasmid might be 5,000 bp. Longer templates weigh more per molecule, so the same mass concentration contains fewer copies. Molecule type is required because double- and single-stranded molecules use different average base weights. A common mistake is using a dsDNA length while selecting ssDNA. PCR cycles is required as an integer from 0 to 60. More cycles increase the idealized count by a factor of two per cycle; zero cycles leaves the starting count unchanged.

Output guide

DNA copies is the estimated number of molecules per microliter and is driven by concentration, length, and molecule type. A higher value means more template molecules in the same volume. Template molecular mass is the approximate grams per mole of one full-length molecule, calculated as length multiplied by average base weight. PCR fold increase is the exact mathematical multiplier 2^cycles under ideal efficiency. Copies after PCR multiplies the starting copies/µL by that factor. The PCR cycle projection table lists the cycle number, its multiplier, and the corresponding estimated concentration. These are model estimates, not a promise of experimental yield; the NCBI overview of PCR amplification explains why reactions leave the exponential phase and develop a plateau.

Worked example

Learn more

The NIST explanation of the mole and Avogadro constant describes why one mole corresponds to exactly 6.02214076 × 10²³ specified entities. For broader laboratory context, the NCBI Polymerase Chain Reaction review summarizes PCR principles, applications, and practical limitations.