How much memory capacity is in a human brain?

Usually enough unless it has been improperly used or experienced some sort of trauma. If this is the case, I recommend you contact the manufacturer and request a replacement.

1 gigglebite

As for long term memory the possibilities are endless. But there are three types of memory the brain uses, long term, short term and working.

Working is the go-between of long and short term. It is held that the working memory can hold 5 pieces (+ or - 2) of information at one time. Once the working memory has reached capacity, either the information is transferred to long term memory or it is discarded.

Immeasurable.

Sensory memory- .5 to 3 seconds
Short term memory- a minute or two, it can hold 5-9 bits of information- rehearsal will keep it in the short term, rehearsal for a long time or if it has great emotional value, it will go to long term
long ter memory- endless

Try this: Look at these letters for 30 seconds, then look away and solve this math problem: 3x +6= 12 x=?

ABC.NFL.NBA.CNN.USA.TBS

Now write down all the letters you remember. (Your short term only remembers 5-9 items, since these letters are familiar in the USA, you'll be able to remember more items if you give them meaning!)

Enough to remember every hurt and insult, no matter how minor.

Not enough to remember where the hell your car keys are.

immense capacity but it diminishes as you become old.

Possibilites = many trillions of synaptic connections.

http://www.leaderu.com/truth/2truth03.html
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TCY-4CG797W-M&_user=10&_coverDate=09%2F01%2F2000&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=baf0e4dd1989ec30ade829f4580b8638

According to the following quotes I don't think you need worry about running out of space.

The Franklin Institute's Center for Innovation in Science Learning says: "The human brain is able to continually adapt and rewire itself. Even in old age, it can grow new neurons. Severe mental decline is usually caused by disease, whereas most age-related losses in memory or motor skills simply result from inactivity and a lack of mental exercise and stimulation."

James Watson, co-discoverer of the physical structure of DNA said ." The brain is the most complex thing we have yet discovered in our universe."

"A book by neuroscientist Gerald Edelman explains that a section of the brain the size of a match head "contains about a billion connections that can combine in ways which can only be described as hyperastronomical—on the order of ten followed by millions of zeros."

In Gigabytes?

I'm eleven and I have been working on this for a bit, there is an answer, approximately 1.1 Quintillion MB of Internal Memory which is 1,100,000,000,000,000,000MB !