How big a tarp for one person?

Based on this question: Best tarp setup for camping on the plains? I wonder how big a tarp I need to carry for one person, for emergency use only.

I am hoping to do a multi day hike where I will usually sleep under roofs, like hotels, hostels or even in private homes. For that I expect to carry a good sleeping bag and a light duty mat, just enough to keep me isolated from the ground.
But as I will cross a huge distance solo (I hope from within the Netherlands to Santiago de Compostella, on the west coast of Spain,) I will not be sure to find a roof to sleep under every day and may find myself in bad weather without a lot of advance warning. I would like to know that I can spend the night safe from the weather at need.

I will carry (and likely use) a walking stick, most likely one of the ones you can adjust the length, but want to avoid bringing other supports if I can get away with not having one. If there are usable trees or other supports I will use them, but I might end up in the middle of a campsite without usable supports. I will also have string, more than needed for this, as I am a knot tyer and will always have something to tie with.

I understand the instructions in the linked question, but what I do not understand is how big is the smallest tarp I can get away with for one, not too tall person. (I am 1.65 meter, 5'5", and a little overweight but not in a way that I expect to be of influence in this.)

The other reason to carry a tarp is that I might get into really bad weather and need more protection than my rain gear will provide.

I will appreciate if you can link to examples of tarps for sale as well as or instead of actual size suggestions. And as I am mostly gathering information well in advance of travel, it does not matter to me whether they are in Europe or elsewhere in the world. (Target departure is at least 2 years from now, can be a few years after that.)