Help with new twitter design!!

The new twitter layout with header and other things has been a pain... The header image is very easy to upload, but when i click on change my dp, some window pops up and need to crop out half of my pic... I've tried with various resolutions but always need to crop out! But i've seen many people who have a bigger dp with a greater resolution... So what is the ideal image size for twitter dp??
Thanks in advance...

Just found out that 800 x 800 pixels is the correct size for the display picture in twitter! But i've seen many accounts whose profile picture is much bigger than that! Anyone knows regarding the size thing??