IDT offers a number of free design and analysis tools in the online SciTools suite. The suite is comprised of tools for designing assay components as well as determining the properties of any sequence entered.
The Resuspension Calculator allows you to calculate how much volume (μL) to resuspend a dried oligo at your desired concentration. Enter the quantity of oligonucleotide you have based on OD260, nmoles, or mg. Select the conversion factor and enter the final, desired concentration. The tool will calculate the amount of water or TE buffer you will need to add to your oligo to achieve the concentration you entered.