🧬 DNA Concentration Calculator
Translate UV absorbance measurements into nucleic acid concentrations for downstream workflows.
Provide fragment length to convert mass concentration into µM.
How to Use This Calculator
Measure absorbance at 260 nm
Use a spectrophotometer or microvolume instrument (e.g., NanoDrop) to measure A₂₆₀ for your diluted sample.
Record dilution and path length
Enter the dilution factor applied prior to measurement and the optical path length (1 cm is standard).
Add fragment length for molarity
Provide the DNA length to convert mass concentration into molar concentration if needed for cloning or qPCR.
Formula
Conc (µg/mL) = A₂₆₀ × ε × Dilution ÷ PathLength
Where ε is 50 for dsDNA, 40 for RNA, and 33 for ssDNA (µg/mL per A₂₆₀ unit at 1 cm). To convert mass to molarity:
Conc (µM) = (Conc (µg/mL) ÷ (Length × 650)) × 10³
The factor 650 g/mol per bp approximates the molecular weight of a base pair for double-stranded DNA.
Full Description
UV absorbance at 260 nm provides a fast, non-destructive estimate of nucleic acid concentration. Because proteins and other contaminants can absorb at similar wavelengths, assess sample purity with the A₂₆₀/A₂₈₀ ratio where possible.
This tool converts absorbance measurements into mass and molar concentrations, enabling precise planning for downstream workflows such as PCR, cloning, and sequencing library preparation.
Frequently Asked Questions
What if my path length is not 1 cm?
Many microvolume instruments use shorter path lengths (e.g., 0.05 cm). Enter the exact path length to ensure accurate conversion.
Can I use this for plasmid DNA?
Yes. dsDNA coefficients apply to plasmid DNA. Provide the plasmid length in base pairs if you need molar concentration.
Do I need to blank my instrument?
Always blank with the same buffer used to dilute your sample. This removes baseline absorbance and improves accuracy.
How can I check sample purity?
Examine the A₂₆₀/A₂₈₀ ratio: pure DNA typically falls near 1.8. Lower ratios can indicate protein contamination; higher ratios may reflect RNA or solvent carryover.