The COOLPIX S6400 has 2 different 16 megapixel image mode options with different compression ratios and your choice of ratio will significantly impact the number of pictures will fit on your memory card.
The 16MP option that is indicated with a star in the menu is compressed at a ratio of approximately 1:4 - with this option you will be able to fit about 760 images on an 8GB card.
The 16MP option that is not starred in the menu is compressed at a ratio of approximately 1:8 and with this option you will be able to fit about 1520 pictures on an 8GB card.
Detailed information of these image mode settings and memory card capacity can be found on pages 49 and 50 of the Reference section of the S6400 manual. A list of approved memory cards for the S6400 can be found on page 23 of the Technical Notes and Index section of the manual. A copy of the S6400 manual can be downloaded from this address:http://support.nikonusa.com/app/ans...