You can check few websites which allows to select devices of various mobile brands and screen sizes and some allows to customise the screen size for your testing. Below is list of those websites,
click this link, add your URL on home page, select device of your choice for testing. This is how our website looks on ipad mini.
allows you to select different resolutions.
allows you to check in different predefined devices as well as specifically you can test by selecting portrait and landscape mode.
Allows you to test with changing screen size.