Last updated: July 3, 2026
Resuspension Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The resuspension calculator finds how much solvent to add to lyophilized oligos, DNA, primers, or dry reagents. For molar oligo stocks it uses V(µL) = nmol × 1000 / µM; for mass stocks it uses V(µL) = µg × 1000 / (ng/µL). It also calculates the inverse stock concentration from amount and added volume.
For oligo resuspension, multiply the amount in nanomoles by one thousand and divide by the target micromolar concentration to get microlitres of solvent.
Key Takeaways
- Molar oligo mode uses V(µL) = n(nmol) × 1000 / C(µM).
- Mass mode uses V(µL) = m(µg) × 1000 / C(ng/µL).
- The inverse concentration is amount × 1000 divided by added volume in µL.
- Use molar mode for supplier-reported nmol oligos and mass mode for µg DNA or reagents.
- The primary output is the solvent volume to add in microlitres.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
Molar mode: V(µL) = n(nmol) × 1000 / C(µM); Mass mode: V(µL) = m(µg) × 1000 / C(ng/µL)
Where:
- V=Solvent volume to add(µL)
- n=Amount of lyophilized oligonucleotide(nmol)
- m=Mass of dry reagent or DNA(µg)
- C=Target or resulting stock concentration(µM or ng/µL)
Worked Examples
10 nmol oligo to 100 µM
Default molar mode for a primer tube labelled 10 nmol.
- 1Use V = n × 1000 / C.
- 2Substitute n = 10 nmol and C = 100 µM.
- 3V = 10 × 1000 ÷ 100 = 100 µL.
25 nmol oligo to 100 µM
A larger oligo amount at the same stock concentration.
- 1Use V = n × 1000 / C.
- 2V = 25 × 1000 ÷ 100.
- 3Add 250 µL solvent to make a 100 µM stock.
5 nmol oligo to 50 µM
Lower target concentration with a smaller amount.
- 1Apply the molar resuspension relation.
- 2V = 5 × 1000 ÷ 50.
- 3Add 100 µL to obtain 50 µM.
50 µg DNA to 100 ng/µL
Mass mode for a dry DNA or reagent sample.
- 1Convert mass to ng: 50 µg = 50,000 ng.
- 2Divide by target concentration: 50,000 ng ÷ 100 ng/µL.
- 3Add 500 µL solvent.
20 µg to 200 ng/µL
A compact mass-mode stock preparation.
- 1Convert 20 µg to 20,000 ng.
- 2V = 20,000 ng ÷ 200 ng/µL.
- 3Add 100 µL solvent.
Inverse: 10 nmol in 100 µL
Find the stock concentration after a known volume was added.
- 1Use C = n × 1000 / V.
- 2C = 10 × 1000 ÷ 100.
- 3The stock concentration is 100 µM.
Introduction
A resuspension calculator turns the label on a dry tube into a practical pipetting volume. For lyophilized oligonucleotides and primers, use nmol and µM; for dry DNA or reagent mass, use µg and ng/µL. This tool complements the molarity calculator and concentration calculator by keeping the bench units used on supplier tubes, datasheets, and lab protocols. The unit logic follows IUPAC amount concentration and SI prefix conventions.
What does resuspension mean?
Resuspension means adding a measured solvent volume to a dried pellet, film, or powder so the material becomes a homogeneous stock solution. In molecular biology, this is common for primers, probes, gBlocks, plasmid DNA, and lyophilized reagents. The calculator assumes the amount printed on the tube is accurate and that the added solvent volume dominates the final volume.
Use nuclease-free water for many oligos when short-term storage is sufficient.
Use TE buffer or another validated buffer when long-term stability matters.
Mix gently and allow the pellet to fully dissolve before aliquoting.
Record both stock concentration and solvent volume in your lab notebook.
Molar mode for oligos and primers
Supplier oligo tubes often state an amount in nmol and the desired stock is commonly 10, 50, 100, or 200 µM. Because 1 µM equals 0.001 nmol/µL, the working equation is V(µL) = n(nmol) × 1000 / C(µM). For example, 10 nmol at 100 µM requires 100 µL.
Molar mode does not need molecular weight because nmol already counts molecules.
Mass mode for DNA or dry reagents
When the tube is labelled by mass, convert micrograms to nanograms and divide by the target ng/µL concentration. The equation is V(µL) = m(µg) × 1000 / C(ng/µL). For example, 50 µg at 100 ng/µL requires 500 µL. If you need to connect mass to moles, use a grams to moles calculator or a molar mass calculator.
Finding concentration after adding a known volume
Sometimes you already added solvent or a protocol specifies a fixed volume. In that case, use the inverse relation: C = n × 1000 / V for molar oligo stocks, or C = m × 1000 / V for mass stocks. A 10 nmol primer in 100 µL gives 100 µM, while 20 µg in 100 µL gives 200 ng/µL.
Storage, mixing, and aliquoting tips
After adding solvent, briefly spin the tube so liquid is at the bottom, mix without foaming, and give difficult pellets enough time to hydrate. Avoid repeated freeze-thaw cycles by aliquoting concentrated stocks. Follow supplier guidance such as IDT oligo handling and Thermo Fisher oligo resuspension guidance when available.
For PCR working stocks, many labs dilute a 100 µM master stock to 10 µM to reduce pipetting error.
Common mistakes to avoid
The most common mistakes are mixing nmol with µg, confusing µM with nM, and forgetting that mass mode in this calculator expects target concentration in ng/µL. Another frequent error is using the volume of solvent before wetting a pellet that does not fully dissolve. If concentration controls a downstream dilution, verify with a mole calculator or dilution workflow.
Quick Reference Card
Resuspension — Quick Reference
Quick reference • Resuspension Calculator
Oligo: V = nmol × 1000 / µM; Mass: V = µg × 1000 / (ng/µL)Valid range: Positive nonzero amounts, target concentrations, and volumes; practical volumes usually span 10–2000 µL
Common Values
⚠ Watch Out
- •Do not mix molar mode nmol inputs with mass mode µg inputs.
- •Confirm whether the supplier amount is total nmol, OD units, or mass before calculating.
- •Use nuclease-free solvent and sterile technique for nucleic acid stocks.
- •Very small calculated volumes can be hard to pipette accurately; consider a lower stock concentration.
- •Make sure the pellet is fully dissolved before assuming the stock is homogeneous.
Pro Tips
- →Briefly centrifuge tubes before opening so the dry pellet is at the bottom.
- →Prepare a concentrated master stock, then make single-use working aliquots.
- →Label stocks with concentration, solvent, date, and freeze-thaw count.
- →Use low-bind tubes for low-concentration oligos or precious reagents.
- →Let stubborn lyophilized pellets hydrate for several minutes before vortexing gently.
FAQs
How much water do I add to a 10 nmol primer for 100 µM?
Add 100 µL. The molar formula is V = 10 × 1000 ÷ 100 = 100 µL.
Why is there a factor of 1000 in oligo resuspension?
Because 1 µM equals 1 nmol/mL, which is 0.001 nmol/µL. Dividing nmol by 0.001 introduces the ×1000 factor when volume is reported in µL.
What solvent should I use for primers?
Use the solvent recommended by the supplier or protocol. Nuclease-free water is common for routine use, while TE buffer can improve long-term storage stability for many DNA oligos.
Can I use this for plasmid DNA or genomic DNA?
Yes, use mass mode when your dry amount is in micrograms and your desired concentration is in ng/µL.
How do I calculate concentration if I already added volume?
Choose resulting concentration mode. For oligos, C = nmol × 1000 ÷ µL; for mass, C = µg × 1000 ÷ µL.
Does molecular weight matter for molar oligo resuspension?
Not if the supplier gives amount in nmol. Molecular weight is only needed when converting between mass and moles.