DNA Copy Number Calculator

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Use this calculator to turn DNA or RNA mass into copy number, reverse-calculate mass needed, or plan a dilution to a target copies per uL.

Choose whether you want copies from a measured amount, amount from a target copy count, or a dilution plan to hit a target copies per uL.
This sets the average mass used for each base or base pair. Double-stranded DNA uses base pairs. Single-stranded DNA and RNA use nucleotides.
Use base pairs for double-stranded DNA. Use nucleotides for single-stranded DNA or RNA.
Choose whether your measured amount is a concentration or a total mass.
Used when Amount entered as is Concentration.
Needed for total copies from a concentration, and for dilution planning from a stock solution.
Used when Amount entered as is Total mass.
For reverse calculations, enter the number of molecule copies or target-sequence copies you want.
For dilution planning, enter the concentration you want after dilution.
Advanced options
What your assay counts
Use 1 if each DNA molecule carries one target site. Use 2 or more if the construct or genome carries multiple target sites that your assay counts.
If you set this to 2, then one molecule counts as 2 target copies.
Molecular-weight settings
Default values are standard averages: 660 for dsDNA, about 330 for ssDNA, and about 340 for RNA. Change this only if you have a method-specific value.
Dilution details
For dilution planning, include any liquid already present before you add stock.
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How to use our DNA Copy Number Calculator

  1. Choose What do you want to calculate?, then pick the correct Molecule type and enter Length (bp or nt).
  2. If you are converting from a measured sample, choose Amount entered as and fill in either Concentration (ng/uL) with Sample volume (uL) or Total mass (ng).
  3. If you are solving backward, enter Target copies. If you are planning a dilution, enter Target copies per uL and the desired Sample volume (uL) as your final volume.
  4. Open Advanced options if needed to set Target copies per molecule, change Average mass per base or base pair (g/mol), or include Diluent already in tube (uL).
  5. Click Calculate, then sanity-check the result: longer molecules should give fewer copies for the same mass, and Target-sequence copies per uL should equal Copies per uL times Target copies per molecule.

Definitions

Molecule type: The nucleic acid you are converting: double-stranded DNA, single-stranded DNA, or RNA. This changes the average mass used for each base or base pair.

Length (bp or nt): The size of one full molecule. Use base pairs for dsDNA and nucleotides for ssDNA or RNA.

Copies per uL: Estimated number of whole molecules in each microliter of sample.

Total copies in the sample: Estimated number of whole molecules in the full entered sample amount or volume.

Target copies per molecule: How many assay target sites exist on each molecule. If one plasmid carries two target sites, enter 2.

Target-sequence copies per uL: Copies per uL after multiplying whole-molecule copies by Target copies per molecule.

Average mass per base or base pair (g/mol): The average molecular-weight value used to convert length into molecular weight. Common defaults are about 660 for dsDNA, 330 for ssDNA, and 340 for RNA.

Mass of one molecule: The estimated mass of one complete DNA or RNA molecule in grams.

Mass per base by molecule typeAverage molecular-weight values used in copy-number conversions. Lower mass per base means more copies from the same mass at the same length.Mass per base by molecule typeAverage molecular-weight values used in copy-number conversionsssDNA330 g/molRNA340 g/moldsDNA660 g/molMolecule type
Mass per base by molecule type
Lower mass per base means more copies from the same mass at the same length.

Common mistakes and quick fixes

Mistake: Entering plasmid size in bases for double-stranded DNA but picking the wrong Molecule type .
Fix: Use Double-stranded DNA for plasmids and enter Length (bp or nt) in base pairs.

Mistake: Typing a concentration into Total mass (ng) or a total amount into Concentration (ng/uL) .
Fix: Check Amount entered as first, then fill only the matching input for that mode.

Mistake: Forgetting that Sample volume (uL) affects Total copies in the sample and dilution results.
Fix: Enter the actual volume you have or want as final volume before reading Total copies in the sample or Stock volume to add .

Mistake: Leaving Target copies per molecule at 1 when your assay target appears more than once on each plasmid or genome.
Fix: Change Target copies per molecule to the real number of target sites so Target-sequence copies per uL is correct.

Mistake: Expecting dilution mode to make a stock more concentrated than it already is.
Fix: If Target copies per uL is above the stock Copies per uL , use a more concentrated stock instead of simple dilution.

Mistake: Overriding Average mass per base or base pair (g/mol) with a random value.
Fix: Keep the default unless you have a method-specific reason, because this setting changes Mass of one molecule and every copy-number result.

Limitations & Key Assumptions / Boundary Conditions

  • Results are theoretical copy estimates from mass, length, and average molecular weight, not a direct count of amplifiable templates.
  • The calculator assumes the entered Length (bp or nt) describes one full molecule and that the sample is mostly that molecule.
  • Default average masses are simplified averages. Exact sequence composition, modifications, salts, and preparation method can shift real molecular weight.
  • In Copies from amount mode, concentration-based results depend on the entered Concentration (ng/uL) and Sample volume (uL); mass-based results depend on Total mass (ng).
  • Target-sequence copies per uL is only as accurate as the entered Target copies per molecule. If the target site count is wrong, the sequence-copy output will also be wrong.
  • Dilution mode assumes simple mixing and enough stock is available. It cannot increase concentration above the stock level by dilution alone.
  • If liquid is already present in the tube, an entered Diluent already in tube (uL) that is too large for the planned final volume can make the requested setup impossible.

Methodology

Core equations

The calculator first finds molecular weight from molecule length and the chosen average mass per base or base pair.

MW = L x W

Here, MW is molecular weight in g/mol, L is Length (bp or nt), and W is Average mass per base or base pair (g/mol).

For concentration input, it converts nanograms per microliter into copies per microliter with Avogadro's constant.

copies per uL = (c x 1e-9 / MW) x 6.02214076e23

For total mass input, it converts nanograms into total molecule copies.

total copies = (m x 1e-9 / MW) x 6.02214076e23

If concentration and volume are entered, total copies come from copies per microliter times volume.

total copies = copies per uL x sample volume

If your assay target appears more than once on each molecule, the calculator converts whole-molecule copies into target-sequence copies.

target-sequence copies = molecule copies x target copies per molecule

For reverse mode, it rearranges the same relationship to find mass needed for a requested copy count.

mass needed (ng) = (target copies / target copies per molecule) x MW / 6.02214076e23 x 1e9

If Sample volume (uL) is provided in reverse mode, concentration needed is the required mass divided by volume.

concentration needed (ng/uL) = mass needed / sample volume

Dilution planning

In dilution mode, the calculator first finds the stock concentration in copies per microliter from the entered mass concentration, then uses the standard dilution relationship.

stock volume to add = (target copies per uL x final volume) / stock copies per uL

The entered Sample volume (uL) is treated as the desired final volume. Added diluent is whatever volume remains after subtracting stock volume and any Diluent already in tube (uL).

Mini example

Suppose you have dsDNA of length 3000 bp at 10 ng/uL. Using 660 g/mol per bp, the molecular weight is 3000 x 660 = 1,980,000 g/mol. That gives about 3.041 x 10^9 molecule copies per uL. If each molecule has 2 target sites, then Target-sequence copies per uL is about 6.083 x 10^9.

Assumptions used

The calculator uses average nucleic-acid masses and treats copy number as a theoretical molecule count from mass. Real qPCR behavior can differ because of fragmentation, inhibitors, damaged templates, or non-amplifiable molecules.

Sources

  1. Nucleic Acid Concentration & Molar Converter - Westlab
  2. DNA template nmol dilution using stock solutions quantified in ng | Science Primer - Scienceprimer
  3. DNA Copy-Number Molarity Converter - Efbpublic