Clothing donations - how much is too much?

I have a big family and we drop off probably 100-150+ articles of clothing a year to St. Vincents.  If I itemize it all that could be like a $1000-$1500 deduction.  This is the first time I have used this software.  Is that possible?  Is that legal, do other people take large deductions for clothing drop off?  Thanks for any information.