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Calculation tips for resuspending and diluting nucleic acids

Below are some of the common calculations we use when we work with oligonucleotides in our labs.

Making a 100 μM solution. To resuspend your oligonucleotides to 100 μM, simply multiply the number of nmoles by 10 to get the volume (in μL) of water or buffer to add. For example, assuming you have an oligonucleotide of 1 nmole final yield:

You can prove to yourself that this is the correct volume with the following equivalencies:

Combining (1) and (2), 

Therefore, 1 nmol in 10 µL gives 100 µM.

Calculating nmoles. To calculate nmoles when only the OD (absorbance at 260 nm) and extinction coefficient are provided:


Calculating micrograms. To calculate micrograms (μg) of an oligo when nmoles and molecular weight (g/mol) are provided:

Calculating copy number.
 To calculate the number of copies of your DNA sequence when moles are provided:

Calculating concentration. To calculate the concentration (μM) when molecular weight (g/mol) and concentration in μg/μL are provided:

*Concentration equivalencies for μM = μmoles/L –OR– pmoles/μL (see math below):

You can access a free, online resuspension calculator under the Tools tab at www.idtdna.com, or go to www.idtdna.com/scitools.

Additional reading

Read more articles about handling oligos in our Oligo Handling and Applications section. Here are some examples of what you will find there:

Troubleshooting Polyacrylamide Gel Electrophoresis (PAGE)—Our gel electrophoresis team provides an extensive troubleshooting guide for the PAGE issues they have come across during their work.

 RxnReady Oligos—Get Your Oligos Premixed!—Have 2–6 standard desalted DNA oligonucleotides premixed in a single tube according to your specifications. This can be useful when performing multiplex PCR, or when generating sets of insertions or deletions through site-directed mutagenesis. 

Understanding Melting Temperature (Tm)—Advice from our own Dr Richard Owczarzy on considerations for better oligo design: oligo concentration, salt, SNPs. 


Author: Stephanie Youtsey is a Technical Support Representative at IDT.

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