Understand the relationship
The reasoning behind the result
A ratio compares wavelengths, not mass
The numerator is absorbance at 260 nm. Dividing by absorbance at 280 or 230 nm describes the relative shape of those three recorded measurements. This operation is different from converting A260 to a nucleic-acid mass concentration.
The same arithmetic applies to DNA and RNA records. Interpretation depends on the sample, buffer, pH, instrument and downstream use, so the tool reports measured relationships rather than labelling a sample pure or contaminated.
A small denominator magnifies uncertainty
R = A260/Aλ
When the denominator is close to zero, a small background or measurement difference can cause a large ratio change. Showing only a ratio would hide that sensitivity. The detailed table therefore retains all three absorbances.
A zero or negative corrected denominator does not support the intended positive absorbance comparison and is rejected. The blank-correction tool remains available for inspecting signed measurements rather than forcing them into a purity ratio.
Read the visual as three measurements
The visual shows the entered absorbance values at their stated wavelengths. It is a set of discrete measurements, not a reconstructed continuous spectrum or an identification of particular contaminants.
Matching dilution and path-length normalization matter. Ratios cancel a common scaling factor, but they do not cancel wavelength-dependent errors or an inconsistent blank.
Follow the numbers
One sample, two different comparisons
- DNA A has corrected A230 = 0.45, A260 = 0.90 and A280 = 0.50.
- A260/A280 = 0.90/0.50 = 1.8; A260/A230 = 0.90/0.45 = 2.
- The values describe the measured wavelength ratios. No concentration, contamination identity or experimental acceptance decision follows from the arithmetic alone.
Keep the three measurements with the ratios so another person can check the comparison and its signal level.
Quick guide
How to use this calculator
- Enter blank-corrected values at 230, 260 and 280 nm from matching measurements.
- Inspect both ratios alongside their actual denominator absorbances.
- Interpret them using the instrument and downstream assay context; the calculator does not assign a purity grade.
Calculation method
Calculation and interpretation
Compare measured absorbance at three wavelengths while preserving the denominators and measurement limitations.
A260/A280 = corrected A260 ÷ corrected A280; A260/A230 = corrected A260 ÷ corrected A230
Worked example
One sample, two different comparisons
Keep the three measurements with the ratios so another person can check the comparison and its signal level.
A260/A280 = corrected A260 ÷ corrected A280; A260/A230 = corrected A260 ÷ corrected A230
Supported inputs
Precision and limits
Measurement controls
Entered signals must have a suitable background correction and remain within the measurement system's established working range. Saturated or incompatible measurements cannot be repaired by a ratio.
Biological interpretation
A relative signal, absorbance ratio or calculated loading volume does not establish sample purity, gene expression, mechanism, statistical significance or experimental validity.
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