You can see this link:
https://www.mathworks.com/matlabcentral/answers/126295-memory-usage-in-sparse-matrix
Repeated for convenience with complex info:
The minimum data storage requirement formula for a double m x n sparse matrix with nnz non-zero elements, including the index data, is as follows on a 32-bit system:
bytes = max(nnz,1) * (4 + 8) + (n+1)*4
Which breaks down as follows:
nnz * 4 = Storing the row index of the non-zero elements
nnz * 8 = Storing the non-zero double element values themselves
(n+1)*4 = Storing the cumulative number of non-zero elements thru column
For 64-bit systems using 8-byte integers for the indexing you can replace the 4's above with 8's.
This is just the minimum requirements. A sparse matrix can have excess memory allocated beyond the minimum if desired.
If the variable is complex double, then replace the 8 in the above formula by 16.
If the variable is logical, then replace the 8 in the above formula by 1.
