Its probably 60GB, and if you calculate the 1000/1024 difference you would have 55.87GiB. Keep in mind that disks including SSDs keep some capacity to themselves for internal usage, making the SSD much faster in random write situations.
Since flash memory just follows the 1024-rules of numbers (powers of 2) there should be no reason a 64GB drive is actually 64GiB (and not 59,6GiB). So the first models were labeled 32/64/128/256 etc. But they soon found out its better to stick to known HDD capacities. Not only because it makes comparing more easy, but also because the SSD can use reserve flash cells both to accelerate writing, and perform wear-leveling and recovery operations.
In other words, your SSD has more capacity than it will let you use, which is necessary to make a good SSD.
One bit of (recent) news which might be of interest...
IBM now offers an SSD option for some of it's Power Servers, but only 69Gig of the 128Gig SSD is useable, the rest is used for wear leveling to maintain performance and ensure an "acceptable" product life.
That's alot of overhead, its probably not due to wear-leveling, but likely they use a huge pool of empty flash cells to accelerate random writes. But IMO it should be labeled as a 64GB disk instead, its all about usable capacity, not raw capacity.