What is the right way to calculate 1080p 720p 360p 240p quality?

I'm working on a video hosting project and I would like to know if I'm converting my videos quality the right way.

my equation is: newY=(y/x)*newX

so 1080p is:

    1080x460
   than 720p
    720x306
   ...
    480x204
    360x154
    240x102
    144x60

My problem is 360 and below comes out in a terrible quality. comparing that to youtube I'm wondering if they are actually changing the video resolution or just changing the kb/s?

Solution 1:

1080 describes the vertical resolution of a video. In your question you're using it as the horizontal resolution. As techie mentioned in the comments, common video resolutions include:

• 1920 x 1080
• 1280 x 720
• 720 x 480
• 480 x 360
• 640 x 360

Solution 2:

Use x264 (an H.264 encoder) with constant quality.

In x264, this mode is called Constant Rate Factor. Lower values mean better quality. Use around 19–22 for very good quality. The default is 23.

Convert your video with Handbrake, VidCoder, Ripbot264, TEncoder, FFmpeg, etc.