I recently created a template to be used for t-shirt design, the template was 40cm by 50cm

however when i zoom in to 100% the thing appears absolutely colossal! strangely enough the thing actually seems to appear in better proportions at 25% zoom.

im sure there is a very simple explanation for this, I should add that ive only really been getting familiar with gimp over the past couple of months.

any help or insights would be hugely appreciated.

cheers.

see: https://docs.gimp.org/2.10/en/gimp-view-dot-for-dot.html

Gimp works in pixels not centimetres so the size of your image in pixels depends on the resolution you set up when first making the canvas.

For printing on a t-shirt a resolution of 200 ppi would be ok, 40x50 cm gives an image 3150x3937 pixels.

In a standard set-up 1 image pixel = 1 monitor pixel. Your computer monitor might be 1920x1080 (or less) so at 100% zoom you only see part of the image.

To see what the image looks like printed, keep 100% zoom but change View -> Dot-for-Dot off.

Easier to check if you experiment with a smaller image. This one 10 cm x 10 cm (787x787 px) @ 200 ppi https://i.imgur.com/QVtlEI5.jpg

Now turning dot-for-dot off I can see what a print looks like and as a check measure the physical size on the monitor https://i.imgur.com/PPqVe2h.jpg

All depends that your monitor setup is correct. Gimp 2.10 is much better than earlier versions but do check in Edit -> Preferences -> Display -> Monitor Resolution.