What is the size of the texture trail?

its 128x128 but at least i prefer makin textures in bigger sizes (256x256x and 512x512) and then resizing down makes it easier

^That.
It also depends on which item you have. If you have 256x256 then you would make a 256x256 image. Or like Danzos said, make one larger and resize it down.

Here is a template. of 128x128.
http://forum.toribash.com/tori_textures.php
Here is the link to the textures and templates where you can see the different sizes.