How this calculator works
At 260 nm and a 1 cm path, an absorbance of one corresponds approximately to 50 ug/mL dsDNA, 33 ug/mL ssDNA or 40 ug/mL RNA. A custom molar extinction coefficient and molecular weight replace this average conversion. Absorbance should already have its blank and appropriate background removed. If an instrument reports absorbance normalized to 1 cm, enter 1 cm rather than its physical microvolume path.
Formula
C (ug/mL) = A × conversion factor × dilution / path (cm). Custom conversion factor = molecular weight (g/mol) × 1,000 / epsilon (L/(mol cm)). One ug/mL equals one ng/uL.
Worked example
For dsDNA, A260 = 0.20, a 1 cm path and 40-fold dilution give 0.20 × 50 × 40 = 400 ug/mL. For RNA at A260 = 0.5 without dilution and with a 0.5 cm path, the estimate is 40 ug/mL.
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Frequently asked questions
Does UV absorbance distinguish DNA from RNA?
No. Mixed nucleic acids and UV-absorbing contaminants can inflate the estimate. Use a selective assay when the distinction matters.
Which dilution factor should I enter?
Use total diluted volume divided by the volume of original sample. One part sample plus 39 parts diluent is a factor of 40.
What if absorbance is negative after blanking?
Check the blank and the measurement. The physical concentration model cannot interpret negative absorbance as a negative amount of nucleic acid.