Recent  study “2010 State of Inbound Marketing”

Based on the study, between 100 and 500 Twitter followers is enough followers to realize a rise in leads. Companies within this range of followers, generally experienced 146% more monthly leads than those with between 21 and 100 followers. Typically, a business with up to 20 Twitter followers will generate 11 leads per month, while those with between 100 and 500 will get 35.

An interesting finding of the study was; if the number of Twitter followers exceeds 500, there is no discernible rise in leads. Actually, businesses with 501 or more followers witnessed a 9% decrease in leads to 32 per month. This is potentially down due to the ratio of highly engaged followers being diluted.