Keep a photo's proportions while resizing it. Learn what aspect ratio controls, why dimensions change together and when a separate crop is needed.
Understand the relationship between dimensions
Aspect ratio describes the relationship between width and height. A 1200 by 800 image and a 600 by 400 image share the same 3:2 ratio. Their pixel counts differ, but objects keep the same shape when one is scaled into the other.
Changing that photograph to 600 by 600 without cropping forces its rectangular contents into a square. Faces may become narrow, circles can appear oval and a product may no longer look like the original. A smaller file is not a useful result if its proportions are misleading.
Keep the ratio option enabled
Select the source in Image Resizer and leave Preserve aspect ratio checked. Enter only the dimension that matters most for your placement. For a space limited to 900 pixels wide, enter 900 as the width and let the tool calculate the height.
If the calculated height exceeds a second limit, enter the allowed height instead. A 1600 by 900 photograph fitted within an 800 by 600 area becomes 800 by 450. The unused space belongs to the surrounding layout; the resizer does not add a background canvas to fill it.
Distinguish resizing from cropping
Cropping changes which part of the image is visible. Resizing changes the dimensions of the full image. ToolNivo Image Resizer scales the entire source and does not let you choose a crop boundary.
When a square placement is mandatory, first create a square crop with your preferred editor, then resize it. Consider whether the crop removes part of the subject or essential text. Do not disable the ratio setting merely to force numbers that conflict with the source composition.
Check ordinary shapes in the preview
Inspect an object whose shape you know: a plate, window, logo or person's face. It should look proportionally the same in the result and original. Download the image only after checking that the dimensions meet the requirement and the composition still communicates what you intended.