DNA Concentration Calculator
Nucleic acid concentration and purity from UV absorbance.
That is 25 ng/µL (µg/mL = ng/µL). Using the dsDNA factor of 50 µg/mL per A₂₆₀ unit, at 1× dilution.
Nucleic acid concentration is c = A₂₆₀ × factor × dilution, where the factor is 50 for dsDNA, 33 for ssDNA, and 40 for RNA. An A₂₆₀ of 1.0 therefore ≈ 50 µg/mL of dsDNA. So dsDNA at A₂₆₀ 0.5 with no dilution gives 0.5 × 50 × 1 = 25 µg/mL (25 ng/µL).
How UV quantification works
Nucleic acids absorb ultraviolet light most strongly at 260 nm, because the aromatic bases are excellent UV chromophores. On a 1 cm path length, the absorbance at 260 nm (A₂₆₀) is directly proportional to how much nucleic acid is in the beam, so a single reading converts straight into a concentration once you apply the right conversion factor.
Each nucleic acid type absorbs a little differently, so the factor changes: double-stranded DNA uses 50, single-stranded DNA 33, and RNA 40 µg/mL per A₂₆₀ unit. Multiply by the dilution factor if you diluted the sample before reading.
factor = 50 (dsDNA), 33 (ssDNA), 40 (RNA) µg/mL per A₂₆₀ unit; assumes a 1 cm path length
Worked example
Total RNA read at A₂₆₀ = 1.0 after a 10× dilution:
- 1 Pick the nucleic acid type. RNA uses a conversion factor of 40 µg/mL per A₂₆₀ unit.
- 2 Read A₂₆₀ on a 1 cm path. The blanked reading here is A₂₆₀ = 1.0.
- 3 Note the dilution factor. The sample was diluted 10× before reading, so dilution = 10.
- 4 Multiply it out. c = 1.0 × 40 × 10 = 400 µg/mL, i.e. 400 ng/µL.
Conversion factors and purity targets
Standard factors for a 1 cm path length; an A₂₆₀ of 1.0 ≈ 50 µg/mL dsDNA.
| Nucleic acid | Factor (µg/mL per A₂₆₀) | Pure A₂₆₀/A₂₈₀ |
|---|---|---|
| dsDNA | 50 | ≈ 1.8 |
| ssDNA | 33 | ≈ 1.8 |
| RNA | 40 | ≈ 2.0 |
Reading the result and checking purity
Units. Concentration comes out in µg/mL, which is numerically identical to ng/µL — 25 µg/mL is the same as 25 ng/µL — so you can quote whichever your protocol expects without recalculating.
The 260/280 purity check. Dividing A₂₆₀ by A₂₈₀ tests for protein and phenol contamination, which absorb near 280 nm. Pure DNA sits around 1.8 and pure RNA around 2.0; a noticeably lower ratio flags protein or phenol carryover. Many labs also check A₂₆₀/A₂₃₀ (ideally about 2.0–2.2) to catch guanidine, EDTA, or carbohydrate contamination.
Assumptions. The factors assume a standard 1 cm path length and a clean blank. Very high or very low absorbances fall outside the linear range, so dilute concentrated samples to land A₂₆₀ between roughly 0.1 and 1.0 before reading.