How to copy layer dimension proportions in an action Photoshop CC

I am struggling to work out how to do this and I am sure there is a way.

Here is what I want to achieve: I have one image and one document named size. I want the size document (which has already been set up) to show Small, Medium, Large (which will be the sizes of the image in proportion).

I.e. I open an image. Run the action. It opens 'size.psd' and copys the proportions in. for example, small = 10cm x 5cm, med = 20cm x 10cm, large = 40cm x 20cm.

I need it to get the proportions of the opened image and be able to input to a text layer in the 'size.psd'.

Here is what I have tried: Using image size dialog with constrait proportions, tried copying and pasting the values in the document after modifying to each value.

This merely copies the actual value from one image, and pastes into the size. So it does not work when I open another image with different proportions.

Is there anyway to do this?

Thanks in advance for any assistance.

Stephen