Spectrophotometer Pathlength Correction
Correct microplate absorbance readings to a standard one centimetre pathlength.
About Spectrophotometer Pathlength Correction
Microplate readers measure vertically through the liquid, so the pathlength depends on fill volume rather than being fixed at one centimetre as in a cuvette. Correcting for it is what makes plate readings comparable with cuvette values. A 200 microlitre well in a standard 96-well plate has a pathlength near 0.5 cm, so uncorrected readings understate concentration by roughly half.
Formula
Spectrophotometer Pathlength Correction
Beer-Lambert: A = ε·c·l, so correcting to 1 cm means dividing by the actual pathlength
- pathlength
- Liquid depth the beam passes through, set by well volume and area
- extinction coefficient
- Absorbance of a one molar solution over one centimetre
Worked example
With the default values below, Spectrophotometer Pathlength Correction returns Absorbance at 1 cm Pathlength of 0.7852. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Measured absorbanceminimum 0
- 0.42
- Well volumeminimum 1 uL
- 200 uL
- Well diameterminimum 0.1 mm
- 6.9 mm
- Molar extinction coefficientminimum 1 1/M/cm
- 43,824 1/M/cm
Results
- Absorbance at 1 cm Pathlength
- 0.7852
- Actual Pathlength
- 0.5349 cm
- Correction Factor
- 1.8696 x
- Concentration
- 17.9182 uM
- Transmittance
- 38.019%
Step by step
- 1Values used
- 2Spectrophotometer Pathlength Correction
- 3Absorbance at 1 cm Pathlength= 0.7852
- 4Actual Pathlength= 0.5349 cm
- 5Correction Factor= 1.8696 x
- 6Concentration= 17.9182 uM
- 7Transmittance= 38.019
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Spectrophotometer Pathlength Correction calculated?
Beer-Lambert: A = ε·c·l, so correcting to 1 cm means dividing by the actual pathlength Microplate readers measure vertically through the liquid, so the pathlength depends on fill volume rather than being fixed at one centimetre as in a cuvette. Correcting for it is what makes plate readings comparable with cuvette values.
Why does Spectrophotometer Pathlength Correction matter?
A 200 microlitre well in a standard 96-well plate has a pathlength near 0.5 cm, so uncorrected readings understate concentration by roughly half.
What values do I need to enter?
This calculator takes 4 inputs: Measured absorbance, Well volume, Well diameter, Molar extinction coefficient. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.