What formula does the calculator use?

It uses concentration = A260 × dilution factor × 40 ÷ path length in cm.

Why is the RNA factor 40?

For this calculation, 1 OD at 260 nm is treated as 40 µg/mL of RNA.

How is ng/µL related to µg/mL?

The values are numerically equal: 1 µg/mL equals 1 ng/µL.

When should I enter a sample volume?

Enter the total elution volume in µL when you want the calculator to estimate total RNA yield.

What does a reading outside 0.1–1.5 mean?

It is outside the approximate linear range; low readings may be less reliable, while high readings may require appropriate dilution.

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RNA Concentration Calculator (A260, 1 OD = 40 µg/mL)

Beer–Lambert RNA quantitation: c = A260 × dilution factor × 40 / path length, plus ng/µL, total yield, a 0.1–1.5 linear-range check, and the RNA OD260/280 ≈ 2.0 purity reminder. Derived from Marmur & Doty, Sambrook & Russell, Manchester 1995, Thermo Fisher NanoDrop notes. Educational use only.

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Total RNA prep: A260 = 0.4, 1:5 diluted

A 1:5 diluted total-RNA prep reads A260 = 0.4 on a 1 cm cuvette. Concentration = 0.4 × 5 × 40 / 1 = 80 µg/mL = 80 ng/µL of RNA. The 250 µL elution therefore holds 80 × 0.25 = 20 µg total — roughly 20 typical qPCR reactions' worth of input, with the reading inside the 0.1–1.5 linear range. Using the dsDNA constant 50 here would have wrongly claimed 100 µg/mL.

{"result":"RNA concentration = 80 µg/mL (80 ng/µL); total 20 µg in 250 µL.","metadata":{"input":{"a260":0.4,"dilutionFactor":5,"pathLengthCm":1,"sampleVolumeUl":250},"result":{"constantUgMlPerOd":40,"concentrationUgMl":80,"concentrationNgUl":80,"totalUg":20,"measurementQuality":"within linear range (0.1–1.5)"}}}

Weak reading: A260 = 0.08 flags below linear range

An undiluted RNA sample reads A260 = 0.08, below the ~0.1 lower edge of the linear range — noise now contributes a large fraction of the signal. The tool still computes 0.08 × 1 × 40 / 1 = 3.2 µg/mL (3.2 ng/µL) and 0.16 µg in 50 µL, but flags the reading so the sample is re-measured less diluted (or by a fluorometric assay, which is more sensitive at low concentrations).

{"result":"RNA concentration = 3.2 µg/mL (3.2 ng/µL); reading below the linear range — re-measure less diluted or use a fluorometric assay.","metadata":{"input":{"a260":0.08,"dilutionFactor":1,"pathLengthCm":1,"sampleVolumeUl":50},"result":{"constantUgMlPerOd":40,"concentrationUgMl":3.2,"concentrationNgUl":3.2,"totalUg":0.16,"measurementQuality":"below linear range — reading too low for reliable quantitation, measure a higher concentration or a shorter dilution"}}}

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5 options

SettingsAdjust formats, ranges, numbers, and modes.5

A260 AbsorbancenumberRequiredMeasured absorbance of the (diluted) sample at 260 nm, blanked against the RNase-free elution buffer.Dilution FactornumberRequiredSample-to-total dilution before measurement (1 = measured undiluted).Path Length (cm)numberRequiredCuvette path length (1 cm standard; microvolume readers may use 0.1–1 cm).Sample Volume (µL, optional)numberOptionalTotal elution volume in µL; enter 0 to skip the total-yield calculation.Decimal PlacesnumberOptional

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RNA Concentration Calculator (A260, 1 OD = 40 µg/mL)

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1. Total RNA yield from a diluted sample

2. Low A260 reading flagged below the linear range

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