Large:  125px by 182px

<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=D6EQBU6954ZXG" style="background: url(http://i.imgur.com/hcFJc.png); width:125px; height:182px; display:block; cursor:pointer;"></a>

Regular button: 125px by 125px

<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=D6EQBU6954ZXG" style="background: url(http://i.imgur.com/1A8AS.png); width:125px; height:125px; display:block; cursor:pointer;"></a>