Hi, the way custom size works, it always respects the aspect ratio – that’s why there aren’t two boxes. For example, if you have an image that is 4000 x 3000, and you export it to 1000, then it will make make an image that is 1000 x 750, which is the same aspect ratio. If the image is 3000 x 4000, and you export to 1000, then you will get 750 x 1000. Are you getting a different result?