The dimension_unit column indicates the measurement units you are measuring your products.
Etsy accepts the following measurement units:
in
ft
mm
cm
m
yd
inches
Even though these are allowed, Etsy decides which units you are actually allowed to use.
To determine which units Etsy allows for your shop you will need to:
Log into Etsy
Navigate to your listings page
Create or edit a listing
Scroll down to Item Weight
See which units are listed in the boxes
This is what you should see
You need to select one of the units listed on Etsy for your dimensions to be imported. For us, we can only upload using in or inches. You may need to do some testing on your end to find which units work for you.