According to their website, their stand capacities since they made one end safe standing are as so:
The Meerkat Family Stand
4,637
Main Stand (Home)
2,254
Main Stand (Away)
1,888
GH Display Stand
2,
Weston Homes London Road End (Rail Seating)
2,175
Total Capacity without segregation: 13,511
They say there are around 11,300 available for home supporters.
Add in the 1,888 allocated to away fans (though 538 not available for us) and you're at 13,188.
So there's 323 "missing" seats, though I assume these are the usual away segregation plus other seats lost to camera positions, netted off for w/c spaces etc. similar to at Grenoble Road.