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Calculations: Converting from nanograms to copy number

Here is a calculation often used when creating a qPCR standard curve. Link to a free, online tool that will do it for you.

Researchers performing qPCR will often create a standard curve based on nanograms of amplicon, and then need to convert the resulting nanograms detected to copy number.
The formula for making this conversion is:

X = amount of amplicon (ng)
N = length of dsDNA amplicon
660 g/mol = average mass of 1 bp dsDNA
6.022 x 1023 = Avogadro’s constant
1 x 109 = Conversion factor

† The actual oligonucleotide MW (in Daltons or g/mol) is provided on the IDT Spec Sheet for each oligonucleotide and can be substituted for this arithmetic phrase, which only provides an average MW for a sequence of this length.    

It is important to note if using a single stranded DNA (ssDNA) oligo as a template, the molecular weight provided on the IDT Spec Sheet can replace the (N * 660 g/mol) factor in the formula in Figure 1. However, if you want to calculate that factor using the length of a ssDNA molecule, then the average mass would be 330 g/mol, instead of 660 g/mol.

Alternatively, you can create the standard curve based on copy number; e.g., ranging from 102–107 copies, in 10-fold increments. Then you can determine copy number directly from the standard curve.

Let a free copy number calculator do it for you!

A convenient, free-access copy number calculator to convert nanograms to copy number for real time PCR (RT-PCR) was developed by former IDT customer, Andrew Staroscik, who has since left the bench.

The copy number calculator can be found here.

For research use only. Not for use in diagnostic procedures. Unless otherwise agreed to in writing, IDT does not intend these products to be used in clinical applications and does not warrant their fitness or suitability for any clinical diagnostic use. Purchaser is solely responsible for all decisions regarding the use of these products and any associated regulatory or legal obligations. Doc ID: RUO23-1753_001

Published Oct 21, 2013
Revised/updated Feb 27, 2023