A simple utility for Chemists that integrates with Windows Explorer and provides Thumbnail, Preview, Search and other useful features for structure files.
An approximate record count can be added at the center of thumbnails for multi-mol files SDF, RDF and CML. The approximation can be done by getting the byte size of first 4 records (which we are already reading) and dividing the total size of file with the average size per molecule calculated using first 4 molecules. Usually multi-mol files will contain molecules of similar type (and possibly similar size) so this approximation should work.
SDF File Size = 100 KB
Size of first 4 molecules = 8KB => 2KB per molecule
Approx Count = 100/2 = 50 molecules
If there are only 4 molecules then just display 4.
Approximation will be done above 4
Add a plus-minus sign to the approximate value => (±55)
abhimanyusirohi
commented
10 years ago 
An approximate record count can be added at the center of thumbnails for multi-mol files SDF, RDF and CML. The approximation can be done by getting the byte size of first 4 records (which we are already reading) and dividing the total size of file with the average size per molecule calculated using first 4 molecules. Usually multi-mol files will contain molecules of similar type (and possibly similar size) so this approximation should work.
SDF File Size = 100 KB Size of first 4 molecules = 8KB => 2KB per molecule Approx Count = 100/2 = 50 molecules