What should image sizes be at @1x, @2x and @3x in Xcode?

According to my understanding, if the image size is 100 * 100

@1x -> 100 * 100

@2x -> 200 * 200

@3x -> 300 * 300

There is something to understand. By creating 2x and 3x images, you can't expect exact same layout from each iPhone screen. The layout will be different from screen to screen. 1x, 2x and 3x image sizes dealing with only the pixel density of the screen.

Suppose you have an image which is 320 * 70 and you are creating

@1x -> 320 * 70

@2x -> 640 * 140

@3x -> 960 * 210

This will be your output in different screens.

For @3x image increase @1x image size by 3 times!

e.g.

15 x 15 = @1x

30 x 30 = @2x

45 x 45 = @3x

OR

100 x 100 = @1x

200 x 200 = @2x

300 x 300 = @3x

OR

15 x 10 = @1x

30 x 20 = @2x

45 x 30 = @3x

I hope this is helpful to you!

Yes, your understanding is correct.

A standard resolution image has a scale factor of 1.0 and is referred to as an @1x image. High resolution images have a scale factor of 2.0 or 3.0 and are referred to as @2x and @3x images. Suppose you have a standard resolution @1x image that’s 100px × 100px, for example. The @2x version of this image would be 200px × 200px. The @3x version would be 300px × 300px.

For more details you can check this linkhttps://developer.apple.com/ios/human-interface-guidelines/graphics/image-size-and-resolution/