# 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.

## How to convert from nanograms to copy number

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:

Figure 1. Formula for converting from nanograms to copy number.

Where:
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.

RUO23-1753_001.1

### Real-Time PCR handbook

This updated, complete qPCR handbook is full of information to get you on your way to generating great data. Learn how to design your singleplex or multiplex qPCR assay like a pro, how to analyze qPCR data, and more.

Published Oct 21, 2013
Revised/updated Jun 25, 2024