http://www.politicususa.com/2015/12/17/bernie-sanders-history-sets-record-surpassing-2-million-donations.html
"The average donation is $20, and more than 800,000 donors have donated for a second or third time. Only 1.7% of Sanders donors have maxed out and hit the contribution limit. Most impressively, Sanders trails only President Obama 2.2 million donations by the end of 2011 for the overall record."