Calculating this conversion requires you to know the extinction coefficient for your sequence. With this, you can easily convert from your nanomole amount to ODs. To determine the extinction coefficient, you can analyze your sequence using the IDT free, online OligoAnalyzer tool. Results from this analysis will also provide you with nmol/OD260 and µg/OD260 values.
You may also find the following article useful: Calculation tips for resuspending and diluting nucleic acids.
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