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Resuspension Calculator

Chemistry

Calculate the volume of buffer needed to resuspend dried DNA, RNA, or protein to a target concentration. Convert between μg/μL, nM, and copy number.

10 μg
μg
100 ng/μL
ng/μL
0 Da
Da

Volume of Buffer to Add

100
Final Concentration
100
Molar Concentration
151,515.15
μg/mL
100

This calculator computes your Volume of Buffer to Add, Final Concentration, Molar Concentration, μg/mL from the values you enter.

Inputs
Total Mass (dried)Target ConcentrationMolecule TypeMolecular Weight (optional)
Outputs
Volume of Buffer to AddFinal ConcentrationMolar Concentrationμg/mL

What is a Resuspension?

The Resuspension Calculator computes the volume of buffer required to dissolve a dried sample to a target concentration. Enter the total dry mass (μg) and target concentration (ng/μL) to get the volume to add in μL, plus molar concentration for nucleic acids and proteins.

Resuspension is the most frequent calculation in molecular biology — performed every time DNA is eluted from a spin column, RNA is precipitated, or lyophilised reagents are reconstituted. The formula is straightforward: Volume (μL) = Total Mass (ng) / Target Concentration (ng/μL), but unit conversions between ng, μg, nM, and copy number are prone to error. This calculator handles all conversions and optionally computes molar concentration from molecular weight.

For measuring concentration after resuspension using UV-Vis (A260), the Beer-Lambert Law Calculator converts absorbance to concentration using the appropriate extinction coefficients (dsDNA: 1 OD₂₆₀ = 50 μg/mL). For preparing serial dilutions from the resuspended stock, the Dilution Factor Calculator computes the volumes needed.

How to use this Resuspension calculator

  1. Enter Total Mass (μg) — from the kit report (kit will state eluted mass), NanoDrop measurement × volume, or supplier specification on lyophilised product.
  2. Enter Target Concentration (ng/μL) — e.g., 100 ng/μL for a general DNA stock; 10 ng/μL for PCR working solution.
  3. Select Molecule Type for automatic molecular weight assumptions (660 Da/bp for dsDNA; 330 Da/base for ssDNA; 340 Da/base for RNA).
  4. Enter Molecular Weight (Da) if known (plasmid MW = length × 660 Da; oligo MW from supplier).
  5. Add the calculated volume (μL) of TE buffer or nuclease-free water to the dried pellet.
  6. Vortex gently and incubate 5 min at room temperature; spin briefly; measure concentration by NanoDrop to verify.

Formula & Methodology

Resuspension volume calculation:

Volume (μL) = Total Mass (ng) / Target Concentration (ng/μL)             = [Total Mass (μg) × 1000] / Target Concentration (ng/μL)  Molar concentration:   nM = [c (ng/μL) × 10⁶] / MW (Da)   [Derivation: ng/μL = μg/mL = 10⁻³ g/L; M = (10⁻³ g/L)/MW → nM = 10⁶/MW × c]

Worked example — plasmid miniprep from E. coli (standard in Indian NCBS/IIT labs):

Miniprep kit (QIAGEN, HiMedia) elutes in 50 μL buffer. NanoDrop reads 180 ng/μL → total DNA = 180 × 50 / 1000 = 9 μg. Target stock: 500 ng/μL.

Volume of TE to add: V = 9 μg × 1000 / 500 ng/μL = 9000 / 500 = 18 μL (Current volume 50 μL → already too dilute for 500 ng/μL target) Better: spin-concentrate first, or use initial volume directly at 180 ng/μL

If starting from 5 μg dried plasmid (e.g., from ethanol precipitation):

V = 5 μg × 1000 / 500 ng/μL = 5000/500 = 10 μL TE

For a 4500 bp plasmid (MW = 4500 × 660 = 2,970,000 Da):
nM = 500 × 10⁶ / 2,970,000 = 168 nM

This molar concentration is used for ligation reactions (insert:vector molar ratio = 3:1 recommended by NEB, used in Indian CSIR lab protocols).

Frequently Asked Questions

Resuspension is the process of dissolving a dried or pelleted biological material (DNA, RNA, protein, lyophilised reagents) in a known volume of buffer or water to achieve a target concentration. After spin-column purification, PCR cleanup, ethanol precipitation, or lyophilisation, nucleic acids are dried — resuspension in a specific volume gives a known concentration for downstream use. Correct resuspension volume is critical: too little → too concentrated → inhibits downstream reactions; too much → too dilute → insufficient mass for applications.
Enter the Total Mass (μg) of dried material — from the kit report, spectrophotometric measurement, or supplier specification. Enter Target Concentration (ng/μL). Select the Molecule Type (dsDNA, ssDNA, RNA, or Protein). Optionally enter the exact Molecular Weight (Da) if known for accurate molar concentration calculation. The calculator returns the Volume of Buffer to Add (μL), the confirmed final concentration, molar concentration (nM), and mass per volume (μg/mL).
DNA: TE buffer (10 mM Tris-HCl pH 8.0, 1 mM EDTA) — EDTA chelates Mg²⁺ and inhibits DNases, protecting DNA. For PCR or restriction enzymes: nuclease-free water or 10 mM Tris-HCl pH 8.5 without EDTA (EDTA inhibits Mg²⁺-dependent enzymes). RNA: nuclease-free water or 1 mM sodium citrate pH 6.5 — EDTA is sometimes avoided for RNA; RNase-free conditions are critical. Resuspend RNA on ice, aliquot, and store at −80°C. Protein: dialysis buffer matched to next step (PBS, HEPES, MES) — avoid glycerol > 50% which may be too viscous; 20% glycerol is common for freeze-thaw stability.
NanoDrop (UV spectrophotometry): measure absorbance at 260 nm (A260). dsDNA: 1 OD₂₆₀ = 50 μg/mL. ssDNA: 1 OD₂₆₀ = 33 μg/mL. RNA: 1 OD₂₆₀ = 40 μg/mL. Also check A260/A280 ratio (protein contamination: should be ≥1.8 for DNA, ≥2.0 for RNA) and A260/A230 (organic solvent contamination: should be ≥2.0). Qubit fluorometer (Thermo Fisher): more accurate for low concentrations and ignores protein/phenol contamination. Indian biotechnology labs (DBT-funded, industry labs) use NanoDrop 2000 (Thermo Fisher) or BioDrop Duo as standard tools for nucleic acid QC.
Recommended working concentrations: PCR: 10–50 ng/μL template (10–50 ng per reaction, use 1 μL). Restriction digestion: 100–500 ng/μL (1 μg DNA per 20 μL digest). Gel electrophoresis: 50–200 ng/well. Sequencing (Sanger): 100–200 ng/μL (3–7 μL needed = 300–700 ng total). Plasmid stock (storage): 500–1000 ng/μL. Nanopore/Illumina library: 1–10 ng/μL after library prep input. For gene synthesis from Indian suppliers (GenScript India, Eurofins Genomics): they typically resuspend plasmid at 100 ng/μL (= 0.1 μg/μL) and ship at −20°C.
ng/μL = μg/mL = mg/L — these three concentration units are numerically identical. Common conversions: 100 ng/μL = 100 μg/mL = 0.1 mg/mL. For molar concentration: nM = (ng/μL × 1e6) / MW (Da). Example: 100 ng/μL dsDNA of MW 3,000,000 Da (= 4545 bp) → nM = 100 × 1e6 / 3,000,000 = 33.3 nM. For small oligos (20 bp, MW ≈ 13,000 Da): 100 ng/μL = 100 × 1e6 / 13,000 = 7692 nM = 7.7 μM. The [Molarity Calculator](/molarity-calculator/) performs general mass-to-molarity conversions.
Total mass = concentration (ng/μL) × volume (μL) / 1000. Example: NanoDrop reads 150 ng/μL in 50 μL eluate → total DNA = 150 × 50 / 1000 = 7.5 μg. For qPCR standard curve, you need copy number: copies/μL = (ng/μL × 1e9 pg/ng × 1e12 molecules/mol) / (MW in pg/molecule × NA). For a 3000 bp plasmid (MW = 1,980,000 Da = 3.29 × 10⁻¹⁵ g/molecule): copies/μL = 150 ng/μL / (3.29 × 10⁻¹⁵ g/molecule × 1e9 ng/g × 6.022 × 10²³) → simplified: copies = (ng/μL × 6.022 × 10²³) / (MW × 1e9).
The mass-based calculation (Volume = mass / target concentration) applies to any dried or pelleted material where you know the dry mass and want a target concentration. For cell pellets: if you know the dry cell weight (DCW, g/L) of a microbial culture — common in Indian fermentation industry for Saccharomyces cerevisiae, Bacillus subtilis, and E. coli production — you can use this calculator to resuspend to a target OD or dry weight per mL. However, cell density is usually measured by OD600 rather than dry mass. For specific cells: 1 OD600 ≈ 0.3 g DCW/L (E. coli); target OD resuspension requires a different formula.
Very high RNA concentrations (>1 μg/μL) can cause: (1) Increased secondary structure formation — RNA folds on itself, creating hairpins and duplexes that interfere with cDNA synthesis (reverse transcription). (2) Inhibition of downstream reactions — RNA concentration > 1 μg/reaction in RT-PCR often inhibits enzyme. (3) Viscosity — high RNA concentrations make pipetting inaccurate. Recommended RNA concentrations: RT-PCR: 50–500 ng/μL stock; dilute 1:10 for 5–50 ng/reaction. RNA-seq library prep (Illumina): 100–1000 ng/μL of intact high-quality RNA (RIN ≥ 7). Indian genomics facilities (CCMB, NCBS, IndiGen programme) process samples at these concentrations routinely.
TE buffer (Tris-EDTA): pH 8.0 (Tris) maintains slightly alkaline conditions preventing depurination; EDTA chelates Mg²⁺ → inhibits DNases (DNA is stable for years at −20°C). Disadvantage: EDTA interferes with downstream enzymatic reactions requiring Mg²⁺ (PCR, restriction digestion, ligation) — dilute out before use. Nuclease-free water: no inhibitors → DNA less stable at room temperature; risk of DNase contamination if tubes/reagents not RNase/DNase free. Advantage: no downstream inhibition. Best practice: make concentrated stocks in TE (500–1000 ng/μL), dilute working aliquots in nuclease-free water to 10–50 ng/μL for daily use. Store stocks at −20°C; working aliquots at 4°C.