DNA Molarity Calculator
This DNA molarity calculator converts DNA concentration (ng/µL or µg/mL) and the number of base pairs into molar concentration (nM, µM, or M). Essential for cloning, PCR setup, ligation reactions, and transfection experiments where stoichiometric DNA amounts are required.
DNA Molarity Calculator
DNA Concentration → Molarity
M = (conc × 10⁻⁶) / (bp × 660) What is DNA Molarity?
DNA molarity expresses the molar concentration of a DNA solution — the number of moles of DNA molecules per liter. Unlike mass concentration (ng/µL), molarity accounts for the size of the DNA molecule.
DNA molecular weight depends on the number of base pairs: 1 bp of dsDNA ≈ 660 Da (daltons). A 5 kb plasmid has a MW of 5000 × 660 = 3,300,000 g/mol.
DNA molarity is critical for calculating molar ratios in ligation reactions (insert:vector ratio), setting up equimolar pools for next-generation sequencing, and optimizing transfection protocols.
DNA Molarity Formula
The DNA molarity formula converts mass concentration and size to molar concentration:
Where ng/µL is the DNA concentration (1 ng/µL = 1 µg/mL = 0.001 g/L), bp is the number of base pairs, and 660 is the average molecular weight per base pair of double-stranded DNA.
For single-stranded DNA (ssDNA), use 330 Da per nucleotide instead of 660 Da per base pair.
The result is typically in nanomolar (nM) or picomolar (pM) range for most lab concentrations.
How to Calculate DNA Molarity
Follow these steps to convert DNA concentration to molarity:
- Measure DNA concentration using a spectrophotometer (NanoDrop) or fluorometer (Qubit). Record in ng/µL.
- Determine the DNA size in base pairs (bp) or kilobases (kb). Check the vector map or gel electrophoresis result.
- Calculate molecular weight: MW = bp × 660 Da/bp for dsDNA.
- Convert concentration: ng/µL = µg/mL = 0.001 g/L.
- Apply the formula: Molarity = (concentration in g/L) ÷ MW.
- Convert to nM: Multiply the result in M by 10⁹ to get nanomolar.
DNA Molarity Calculator Examples
Worked examples for common DNA molarity calculations:
Example 1: A 5 kb plasmid at 100 ng/µL. MW = 5000 × 660 = 3,300,000 g/mol. Conc = 0.0001 g/L. Molarity = 0.0001 / 3,300,000 = 30.3 nM.
Example 2: A 500 bp PCR product at 20 ng/µL. MW = 330,000 g/mol. Molarity = 0.00002 / 330,000 = 60.6 nM.
Example 3: A 10 kb fragment at 50 ng/µL. MW = 6,600,000 g/mol. Molarity = 0.00005 / 6,600,000 = 7.58 nM.
Molarity Calculator Tools
Explore our collection of 20 specialized molarity calculators. Each tool is designed for a specific type of calculation with its own unique input fields and formulas.
FAQs
How do you calculate DNA molarity?
M = (concentration in ng/µL × 10⁶) ÷ (molecular weight in g/mol × 10⁹). For dsDNA, MW ≈ number of base pairs × 660 Da.
What is the molarity of 100 ng/µL of a 5 kb plasmid?
MW = 5000 × 660 = 3,300,000 g/mol. M = (100 × 10⁻⁶) / 3,300,000 = 3.03 × 10⁻¹¹ M ≈ 30.3 nM.
What is the average MW per base pair?
For double-stranded DNA, the average molecular weight is ~660 Da per base pair. For single-stranded DNA, it is ~330 Da per nucleotide.
What units does the DNA Molarity Calculator support?
The dna molarity calculator supports mass units (g, mg, µg, kg), volume units (L, mL, µL, gal), molar mass (g/mol, kg/mol), and molarity units (M, mM, µM, nM, pM, fM, aM).
Is the DNA Molarity Calculator free to use?
Yes. The dna molarity calculator is 100% free, requires no sign-up, and works on all devices. All calculations are performed instantly in your browser.