DNA Copy Number Calculator

Figran

Convert DNA concentration to copies/µL and plan your qPCR standards.

  • Plasmid, gBlock, RNA or genomic DNA
  • Pipettable dilution series
  • Absolute quantification
Calculator inputs
7.2 × 10⁹copies/µL

2.9 × 10⁸ copies per ng · 12.0 nM · MW 2.09 × 10⁶ g/mol

Dilute 1:1,441 for 1.0 × 10⁷ copies in 2 µL

617.96 g/mol/bp + 36.04 convention: 7.7 × 10⁹ copies/µL.

DNA copy number calculator examples

Choose a starting point and adapt it to your experiment.

Linearized plasmid standard

Convert a plasmid stock before preparing standards.

3,165 bp · 25 ng/µL

gBlock gene fragment

Calculate copies in a synthetic DNA fragment.

500 bp · 10 ng/µL

PCR product as a standard

Plan a dilution series from an amplicon.

150 bp · 7 points · 10-fold

Human genomic DNA

Estimate haploid genome copies in a DNA sample.

GRCh38 · 50 ng/µL

E. coli genomic DNA standard

Prepare standards from a bacterial genome.

4.64 Mb · 6 points

Lambda DNA for ddPCR

Estimate a dilution for a digital PCR reaction.

48,502 bp · 20 µL ddPCR

In vitro transcribed RNA standard

Convert an RNA standard from mass concentration.

1,000 nt · 340 g/mol per nt

Synthetic oligo at 1 µM

Convert a molar oligonucleotide concentration.

120 nt · 1 µM

Quantify samples from a standard curve

Calculate unknown copies from measured Cq values.

7 standards × 3 · 4 samples

Bacterial load per ng of DNA

Report copy number relative to input DNA.

6 standards × 2 · 6 samples · 10 ng per reaction

How to calculate copy number for qPCR standards

Prepare a standard series in four steps.

  1. 1Choose a template

    Select the template and enter its length or sequence.

  2. 2Enter concentration

    Convert the stock concentration to copies per microlitre.

  3. 3Standard curve dilution series

    Set the highest standard and number of points.

  4. 4Take the protocol to the lab

    Copy or print the dilution instructions.

How to calculate DNA copy number

Convert mass or molar concentration to molecule count.

Mass concentration
copies/µL=c·10−9·NAL·660
Molar concentration
copies/µL=c·10−9·NA106

For 3,165 bp at 25 ng/µL, the 660 convention gives 7.2 × 10⁹ copies/µL.

Mass conventionCopies per µL
660 g/mol/bp7.2 × 10⁹
617.96 g/mol/bp + 36.04 g/mol7.7 × 10⁹
Sequence-specific molecular weightSequence required

References: Thermo Fisher: Standard Curves · QIAGEN: dsDNA Mass Moles Converter

Absolute quantification from a standard curve

Use measured Cq values to estimate unknown copy numbers.

Standard curve inversioncopies=10(Cq−b)/m
  • Choose standards that cover the sample range.
  • Results below the lowest standard are not extrapolated.
  • Linearize plasmid standards before quantification.

Slope, efficiency, and R² describe standard curve quality. Use the Delta Delta Ct Calculator for efficiency-corrected relative expression.

Standard curveSamples10152025303510¹10²10³10⁴10⁵10⁶10⁷Sample A1Sample B2Sample C3Copies per reactionCq1. Sample A (21.5)1. Sample A (21.5)2. Sample B (27.9)2. Sample B (27.9)3. Sample C (33.6)3. Sample C (33.6)

References: MIQE 2009 · Hou et al. 2010

DNA copy number calculator FAQ

How do I convert ng to copy number?

Divide the mass in grams by molecular weight, then multiply by Avogadro’s constant. For dsDNA, molecular weight is commonly estimated from length multiplied by 660 g/mol per base pair.

Should I use 660 or 650 g/mol per base pair?

Both are approximations. Use one convention consistently and report it; for a sequence-specific molecular weight, paste the sequence.

Which concentration should I use, NanoDrop or Qubit?

A fluorometric assay is more specific for dsDNA. Absorbance can include RNA and free nucleotides; convert an A260 reading to ng/µL before using this tool. To calculate concentration from absorbance, use the Beer–Lambert Law Calculator.

How do I make a 10-fold dilution series for a qPCR standard curve?

Prepare a suitable pre-dilution and then make each tenfold step with volumes your pipette can deliver. Allow enough volume for every replicate. Use the Serial Dilution Calculator for general dilution planning.

How do I keep low-copy standards stable?

Use an appropriate carrier or low-binding tubes and prepare aliquots to avoid repeated freezing and thawing.

How do I calculate copy number from Cq (absolute quantification)?

Fit Cq against log₁₀ copies for the standards, then invert the fitted line. Interpret unknowns within the tested standard range. Slope, efficiency, and R² describe standard curve quality. Use the Delta Delta Ct Calculator for efficiency-corrected relative expression.

How many genome copies are in 1 ng of human DNA?

About 294 haploid copies for a 3.1 Gb genome at 660 g/mol per base pair, equivalent to about 147 diploid cells. Multi-copy targets require their genomic copy number to be considered.

Is plasmid copy number the same as copies of plasmid DNA?

No. Copies in a solution count molecules; copies per cell require quantification of a plasmid target and a single-copy chromosomal target, followed by their ratio.

Can I use this for ddPCR?

Yes, you can plan sample dilutions. Digital PCR software estimates concentration from partition counts without requiring a standard curve.

Plan your next qPCR standard curve

Turn your template concentration into a practical series.

Calculate copy number