Giving default height and width in for croping box

[sidaurukfreddy]

hello been strugling in this issue, already make post in his blog but still no respond so i read all comment in his blog then i found you,

Quick question here is Demo

My question is how can i make box for croping has default height, let say
height : 500px;
width: 500px

Reminder juts for croping box

Thanks