Resizing images in WordPress is a real pain – which is why it’s always good to get the size right before inserting them.
However, if you do want to resize, this how to do it:
1. in the Visual tab of the editor, click the image edit icon:
From here, select the Advanced Settings tab:
From here, you can adjust the width and the height of the image. BUT… ADJUSTING THESE SEPARATELY ALTERS THE ASPECT RATIO OF THE IMAGE.
If you don’t want a disaster like this, read on:
To retain the aspect ratio of the image, you need to adjust the width and height proportionately.
Step 1: Make a note of old_width and old_height. In the example above, old_width is 680 pixels and old_height is 459 pixels
Step 2: Decide what you want new_width to be (let’s say, 400 pixels in this example)
Step 3: Calculate new_height, using new_height = (old_height*new_width/old_width)
In the case above, if old_width is 680 pixels, old_height is 459 pixels and new_width is 400 pixels,
new_height = (459*400/680) = 270 pixels
And here you are: