Calculate the output size in convolution layer
How do I calculate the output size in a convolution layer?
For example, I have a 2D convolution layer that takes a 3x128x128 input and has 40 filters of size 5x5.

you can use this formula [(W−K+2P)/S]+1.


W is the input volume - in your case 128 
K is the Kernel size - in your case 5
P is the padding - in your case 0 i believe
S is the stride - which you have not provided. 


So, we input into the formula:

Output_Shape = (128-5+0)/1+1

Output_Shape = (124,124,40)


NOTE: Stride defaults to 1 if not provided and the 40 in (124, 124, 40) is the number of filters provided by the user.
