What Is the DNA Concentration Calculator?
This calculator estimates the concentration of double-stranded DNA (dsDNA) in a sample from its absorbance reading at 260 nm (A260) measured on a spectrophotometer such as a NanoDrop or a cuvette-based UV instrument. Nucleic acids absorb UV light strongly at 260 nm, and this absorbance is directly proportional to concentration, making it the standard quick method for quantifying DNA in molecular biology labs.
How to Use It
Enter the A260 absorbance value displayed by your spectrophotometer. Enter the dilution factor — if you diluted the sample 1:10 before reading, the factor is 10; if you read it neat, use 1. Optionally enter the total sample volume in microliters to also estimate the total DNA yield. The tool returns the concentration in ng/µL (and the numerically equal µg/mL) plus the total mass.
The Formula Explained
The calculation is $$\text{Concentration (ng/µL)} = A_{260} \times 50 \times \text{Dilution Factor}$$ The factor 50 is the conversion constant for dsDNA: a 1 cm path-length sample with an A260 of exactly 1.0 contains roughly 50 ng/µL of double-stranded DNA. For single-stranded DNA you would use 33 and for RNA 40, but this tool assumes dsDNA. Total yield in micrograms is \(\text{concentration} \times \text{volume} \div 1000\).
Worked Example
Suppose your NanoDrop reads an A260 of 0.5 on a sample diluted 1:10, with a final volume of 50 µL. $$\text{Concentration} = 0.5 \times 50 \times 10 = 250 \text{ ng/µL}$$ $$\text{Total yield} = 250 \times 50 \div 1000 = 12.5 \text{ µg}$$
FAQ
Why 50? It is the empirically established extinction factor for dsDNA at 260 nm and 1 cm path length.
What is the dilution factor if I didn't dilute? Use 1.
Is ng/µL the same as µg/mL? Yes — the two are numerically identical, so 250 ng/µL equals 250 µg/mL.
