Transmittance is given by the equation: 
T = I/Io 
where I is the intensity of the light after it has gone
through the sample & Io is the initial light intensity.

Absorbance is related to the %T:
A = -logT = -log(I/ Io)
Equation Summary

T= (I/Io) = 10-A%T = (I/Io) x 100       A = -log T = log(1/T)
Sample Calculation

If  %T = 95%,  then A = log(100/95) = log(1/.95) = -log(.95)
A = 0.02227
Recall from last week: