You can attach forward hook to get the output size of certain module.
Example:
import torch
import torch.nn as nn

seq = nn.Sequential(nn.Conv2d(1, 2, 3), nn.BatchNorm2d(2), nn.Conv2d(2, 3, 3))

def forward_hook(module, input, output):
    print(output.size())
    
seq.register_forward_hook(forward_hook)
seq(torch.rand(1, 1, 10, 10))

which prints out torch.Size([1, 3, 6, 6]).