DNA Concentration Calculator

How to Calculate DNA Concentration from Absorbance

Calculating DNA concentration is a fundamental skill in molecular biology laboratories. Whether you're working with plasmid DNA, genomic DNA, or PCR products, accurate quantification is essential for downstream applications. Our DNA concentration calculator simplifies this process, but understanding the principles behind it is equally important.

The DNA Concentration Formula

The standard DNA concentration formula for double-stranded DNA is:

Concentration (µg/mL) = A260 × Dilution Factor × 50 µg/mL

For single-stranded DNA or RNA, the extinction coefficient changes to 33 µg/mL instead of 50 µg/mL. This difference accounts for the varying UV absorbance properties of different nucleic acid structures.

Using A260 Values for DNA Quantification

When you calculate DNA concentration from A260 values, you're taking advantage of DNA's natural absorbance at 260nm. Here's the step-by-step process:

1. Measure the absorbance of your DNA sample at 260nm using a spectrophotometer
2. If the sample was diluted , note the dilution factor
3. Apply the appropriate extinction coefficient (50 for dsDNA, 33 for ssDNA/RNA)
4. Multiply these values together to get concentration in µg/mL

Interpreting 260/280 Ratios

While our DNA concentration calculator 260 280 focuses on concentration, the 260/280 ratio provides important quality information:

• Pure DNA: ~1.8 ratio
• Protein contamination: Ratio significantly below 1.8
• RNA contamination: Ratio above 1.8

Practical Applications

Once you calculate concentration of DNA from absorbance, you can:

Advanced Calculations

For researchers needing to calculate copy number from DNA concentration, additional information is required:

Copy Number = (Concentration × 6.022×10²³) / (Length × 650 × 1×10⁹)

Where length is in base pairs and concentration is in µg/mL. This calculation is particularly useful for qPCR standard preparation.