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DNA / RNA Concentration Calculator

Converts an absorbance reading at 260 nm into nucleic acid concentration with the standard factors (dsDNA 50, ssDNA 33, RNA 40, oligonucleotide 33 µg/mL per A260 unit) and a dilution factor, and assesses purity from the A260/A280 and A260/A230 ratios.

When to use

You measured A260 (and optionally A280, A230) on a spectrophotometer or NanoDrop and need the concentration in µg/mL or ng/µL, the total amount in a sample, or a purity check.

Do not use when: The sample is very dilute or contaminated (fluorometric assays such as PicoGreen are more specific), you need the molar concentration of a specific oligo (requires its extinction coefficient), or the reading is outside the instrument's linear range.

Formula

concentration (µg/mL) = A260 × factor × dilution_factor, factor = 50 (dsDNA), 33 (ssDNA), 40 (RNA), 33 (oligo); ng/µL = µg/mL; total µg = ng/µL × µL / 1000; ratios = A260 / A280 and A260 / A230

Beer–Lambert law with the conventional average extinction factors for a 1 cm path (dsDNA 50, ssDNA 33, RNA 40 µg/mL per absorbance unit at 260 nm); for short oligonucleotides the sequence-specific extinction coefficient is more accurate. Pure DNA has A260/A280 ≈ 1.8 and RNA ≈ 2.0; A260/A230 is expected at 2.0–2.2; lower values indicate contamination (protein or phenol at 280 nm; guanidine, phenol, EDTA or carbohydrates at 230 nm).

Inputs

ParameterTypeUnitRequiredDescription
a260numberyesAbsorbance at 260 nm for a 1 cm path length (blank-corrected). NanoDrop-type instruments report the 10 mm-equivalent value. Range: ≥ 0, ≤ 100
dilution_factornumberdefault 1Dilution of the sample before measuring (1 = measured neat, 10 = 1:9). Range: ≥ 1, ≤ 1000000
nucleic_acidenum: dsdna | ssdna | rna | oligodefault dsdnaDetermines the conversion factor (µg/mL per absorbance unit).
a280numbernoAbsorbance at 280 nm; gives the 260/280 ratio (proteins absorb here). Range: > 0, ≤ 100
a230numbernoAbsorbance at 230 nm; gives the 260/230 ratio (salts, phenol, carbohydrates absorb here). Range: > 0, ≤ 100
sample_volume_ulnumberµLnoVolume of the undiluted sample; gives the total amount in µg. Range: > 0, ≤ 1000000000

Outputs

OutputTypeUnitDescription
concentration_ug_per_mlnumberµg/mLa260 × factor × dilution_factor.
concentration_ng_per_ulnumberng/µLSame value: 1 µg/mL = 1 ng/µL.
conversion_factornumberµg/mL per A26050 (dsDNA), 33 (ssDNA), 40 (RNA) or 33 (oligo).
ratio_260_280numberPurity ratio: ≈1.8 for pure DNA, ≈2.0 for pure RNA (when a280 is given).
ratio_260_230numberPurity ratio: 2.0–2.2 expected (when a230 is given).
purity_assessmentstringInterpretation of the available ratios.
total_amount_ugnumberµgconcentration_ng_per_ul × sample_volume_ul / 1000 (when the volume is given).

Example

dsDNA, A260 0.5 at 1:10 dilution, A280 0.27: {"a260":0.5,"dilution_factor":10,"nucleic_acid":"dsdna","a280":0.27,"sample_volume_ul":50} → {"concentration_ug_per_ml":250,"concentration_ng_per_ul":250,"conversion_factor":50,"ratio_260_280":1.85,"total_amount_ug":12.5}

RNA, A260 1.2 neat, A280 0.6, A230 0.55: {"a260":1.2,"nucleic_acid":"rna","a280":0.6,"a230":0.55,"sample_volume_ul":50} → {"concentration_ug_per_ml":48,"ratio_260_280":2,"ratio_260_230":2.18,"total_amount_ug":2.4}

GET https://tttkmbb.com/api/v1/calculate/dna-concentration?a260=0.5&dilution_factor=10&nucleic_acid=dsdna&a280=0.27&sample_volume_ul=50

Machine access

Sources

FAQ

Is ng/µL the same as µg/mL?

Yes: 1 µg/mL = 1,000 ng / 1,000 µL = 1 ng/µL, so the two outputs are always identical.

Do I enter the diluted or undiluted volume?

sample_volume_ul is the volume of your original (undiluted) sample; the dilution used only for the measurement is handled by dilution_factor.

What if the 260/280 ratio is low?

Values well below 1.8 (DNA) or 2.0 (RNA) usually mean protein or phenol carry-over; note that the ratio is also affected by pH and ionic strength of the blank, and high concentrations of pure DNA can still read slightly below 1.8.

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