How to find the size of a tensor in bytes?
Step 1 :Get the dtype of the tensor. This will tell you about the number of bytes e.g.float64 is 64 bits = 8 Bytes.

Step 2 Get the shape of the Tensor. This will give you the number of place-holders of the dtype. lets's assume shape = m x n x p
Count of the placeholders is C = m * n * p
Memory = 8 * C => Memory = 8 *m * n * p Bytes.

See this excerpt from Deep Learning with Python, by Francois Chollet


  A 60-second, 144 × 256 YouTube video clip sampled at 4 frames per second would have 240 frames. A batch of four such video clips would be stored in a tensor of shape (4, 240, 144, 256, 3). That’s a total of 106,168,320 values! If the dtype of the tensor was float32, then each value would be stored in 32 bits, so the tensor would represent 405 MB