What you are given
- A260: 1
- Nucleic acid: dsDNA (x50)
- Dilution factor: 50
Formula: c = A260 x factor x dilution
Molecular biology
How do you calculate DNA concentration from A260?
concentration = A260 x OD factor x dilution. The OD factor is 50 ug/mL for double-stranded DNA, 40 for RNA, and 33 for single-stranded DNA. The 260/280 ratio tells you about purity, not amount.
Worked example
Every number below is computed by the calculator, not typed in
The working
- Apply OD factor:
conc = 1 · 50 (dsDNA) · 50=2500 µg/mL
Your sample is 2500 µg/mL.
What each symbol means
- c: Concentration (ug/mL)
- A₂₆₀: Absorbance at 260 nm
- f: OD factor for nucleic acid type (ug/mL per A260)
- D: Dilution factor
A printable one-page version is on the formula sheet.
Where this usually goes wrong
- Using the dsDNA factor of 50 for RNA or for an oligo, which overstates the concentration.
- Forgetting the dilution factor when the sample was diluted to get into range.
- Reading a 260/280 ratio as a concentration. It is only a purity indicator.
Try it yourself
Two problems, with the working revealed
Problem 1 Nucleic acid (A260)
Work out the concentration and the purity ratio.
- A260: 0.5
- Nucleic acid: dsDNA (x50)
- Dilution factor: 50
Show the answer and the working
Your sample is 1250 µg/mL.
- Apply OD factor:
conc = 0.5 · 50 (dsDNA) · 50=1250 µg/mL
Open this in the calculator to change the numbers.
Problem 2 Nucleic acid (A260)
Work out the concentration and the purity ratio.
- A260: 1
- Nucleic acid: dsDNA (x50)
- Dilution factor: 50
Show the answer and the working
Your sample is 2500 µg/mL.
- Apply OD factor:
conc = 1 · 50 (dsDNA) · 50=2500 µg/mL
Open this in the calculator to change the numbers.
Do it with your own numbers.
The Nucleic acid (A260) calculator is free, shows every step, flags the hazards, and works offline once loaded. No account, no signup.
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