What is the size of the logo for custom branding?

What is the size of the logo for custom branding?

Hi,

What is the size of the logo for custom branding, ie how many pixels wide by how many high? If there is no limitation then what is recommended to keep things consistent, ie what is the size of the ZoHo Business logo? Also what image formats can be used, ie png, gif, bmp, jpeg, etc?

Thanks