The dimensions (width and height) is determined by the design of the site. First, look for documentation that specifies image dimensions for the different types of images on your site.

If you don't have that, you can right click on an image and choose Inspect Element. That will tell you the current dimensions of the image.

Wordpress Settings Media Screen

I think they already answered your dimensions question, but to help you with image size, I go to imageoptimizer.net to make them as small as possible. Works for me.

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A scaled image is an image that has been scaled to equal the size that it is displayed.
its better to serve scaled image to prevent browser from resizing it before send it to the visitor which will increase your page speed score and check this out for more image optimizations tip

If you follow the Wordpress doc. link I posted earlier you'll see that WP creates 3 different image sizes each time you upload an image.

Pick whatever size image you need.

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If your site is WP-based, you will find plenty of plugins that will provide you hands-off solution for faster image load..

About page speed: image size google can help you:

Look for those images that can be compressed:
https://developers.google.com/speed/pagespeed/insights/

After see the compression % are you still insterested?? Ok Google's recommendations:

https://developers.google.com/speed/...OptimizeImages

I hope it can help you about the subject page speed

Google Chrome page speed extension will not only tell you what exact images should be compressed, but it also uses google's api to actually compress them fully and gives you the new image fully compressed.

This is the only thing that I have tried that works on every image, 100% of the time. Any other image compression tool including smushit, and even high-level desktop software could not compress every image fully 100% of the time.

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