How do you calculate oligo resuspension volume?

Convert oligo mass to moles using molecular weight, then divide by the target molar concentration. The calculator reports the required solvent volume.

What average molecular weight is used for DNA oligos?

A common rough estimate for single-stranded DNA oligos is about 330 g/mol per base. Exact molecular weight from the supplier is better when available.

Can this calculator be used for RNA oligos?

Yes. The calculator includes an RNA estimate and also allows custom average molecular weight or exact molecular weight.

Oligo Resuspension Calculator

What This Resuspension Calculator Does

This oligo resuspension calculator helps estimate how much solvent to add to a dried DNA or RNA oligonucleotide to reach a target stock concentration. It can also work backwards to calculate concentration or required oligo mass.

moles = mass / molecular weight
volume = moles / concentration

Correct Unit Relationship

A useful shortcut is that 1 µM = 1 pmol/µL. Once the oligo amount is known in pmol, the volume in µL is:

Volume (µL) = amount (pmol) / concentration (µM)

The calculator first estimates or reads the molecular weight, converts mass into moles, then solves the requested value.

Molecular Weight Options

Method	Use when	Typical value
ssDNA estimate	You only know the number of bases.	330 g/mol per base
RNA estimate	You only know the RNA length.	340 g/mol per base
Custom per-base value	Your lab or supplier gives another average.	User-entered
Exact molecular weight	Your supplier provides exact MW.	Best option

Example: Resuspend a DNA Oligo

Suppose you have 10 µg of a 20-base ssDNA oligo and want a 100 µM stock.

Estimated MW = 20 × 330 = 6600 g/mol

Mass = 10 µg = 0.000010 g

moles = 0.000010 / 6600
moles = 1.515 × 10⁻⁹ mol

amount = 1515 pmol

volume = 1515 pmol / 100 µM
volume = 15.15 µL

Practical Notes

Use nuclease-free water or buffer according to your lab protocol.
Check whether the supplier provides nmol, OD, or exact molecular weight.
Very small volumes can be difficult to pipette accurately.
For modified oligos, use the exact molecular weight from the supplier when possible.
For double-stranded products, confirm whether the mass and MW refer to one strand or the duplex.

This calculator does not validate biological sequence chemistry, salt form, hydration state, modifications, duplex formation, or supplier-specific correction factors.

Common Mistakes

Multiplying by molecular weight instead of dividing mass by molecular weight.
Using ng as if it were µg.
Entering concentration in nM while the calculator expects µM.
Using an average MW estimate when exact MW is provided by the supplier.
Trying to pipette volumes below 1 µL without making a more practical stock.

Frequently Asked Questions

What molecular weight should I use?

Use the exact molecular weight from the oligo supplier if available. If not, 330 g/mol per base is a common rough estimate for ssDNA, while RNA is often estimated slightly higher.

Why does the calculator use pmol and µL?

Because 1 µM is equal to 1 pmol/µL. This makes oligo stock calculations convenient.

Can this calculate RNA resuspension?

Yes. Select the RNA estimate or enter the exact molecular weight from your supplier.

What if the calculated volume is very small?

Consider making a lower concentration stock or using a larger amount of oligo. Very small pipetting volumes can create large concentration errors.

Is this a lab protocol?

No. It is a calculation helper. Follow your lab protocol and supplier instructions for actual sample handling.