DNA Concentration Calculator
Nucleic acid concentration, the A260/A280 purity ratio and total yield from a spectrophotometer reading.
An absorbance of 1.
How the dna concentration calculator works
An absorbance of 1.0 at 260 nm in a 1 cm cuvette corresponds to 50 µg/mL of double-stranded DNA, 33 for single-stranded DNA and 40 for RNA. Multiply the A260 by that factor and by any dilution for the concentration; divide by the A280 for purity — pure DNA reads about 1.8, pure RNA about 2.0, and lower means protein or phenol carry-over. Yield is concentration × volume.
Formula: ng/µL = A260 × factor (50 / 33 / 40) × dilution; purity = A260 ÷ A280
Worked examples
| Inputs | Concentration | Note |
|---|---|---|
| A260 0.5, A280 0.27, dsDNA | 25 ng/µL | 25.0 ng/µL, ratio 1.85 |
| RNA, A260 0.8 at 1:10 | 320 ng/µL | 320 ng/µL |
| ssDNA oligo, A260 0.3 | 9.9 ng/µL | 9.9 ng/µL |
FAQFrequently asked questions
What A260/A280 ratio should pure DNA have?
About 1.8; RNA about 2.0. Lower values point to protein or phenol contamination; much higher may mean RNA in a DNA prep, or an unreliable very low reading.
Why 50 µg/mL per absorbance unit?
It is the extinction coefficient of double-stranded DNA at 260 nm in a 1 cm path — a solution of 50 µg/mL absorbs 1.0. Single strands (33) and RNA (40) absorb differently because of base stacking.
What about A260/A230?
A second purity check: pure nucleic acid reads 2.0–2.2. Low values indicate guanidine salts, phenol or carbohydrate carried over from the extraction.
Does a spectrophotometer see contamination?
Absorbance counts anything at 260 nm, including free nucleotides and degraded nucleic acid, so it can overstate usable DNA; a fluorescent dye assay is more specific when accuracy matters.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- CSIRO — Australia's national science agency
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.