Bottom gusseted standup pouch is usually intended to decribe an able-to stand pouch when the prodcts is filled, and with the pleat in the bottom, it will not only be able to hold more products, but also going to present better shelf effect.
Below graphic shows the layer of the most common standup pouch, without any other options, and we are going to give a basic explaination on how the sizes are measured.
Bag Width: from right edge to left edge.
Height: from top edge to bottom
Bottom gusset: In the graphic, the bottom gusset part only show one side of the gusset, for exmple 30mm, however in actual order produce, the bototm gusset should mean the extended size of the gusset, that means 60mm.
For example, if a pouch is described as W110*H160+BG60, that means the sizes of extended bottom gusset is 60mm.
Some options, like the Zipper, tear notch and euro hole, will not have enfluence on the sizes of pouch, however the postion of these options will have to be clearly stipulated in the layout of order before it moves into produce, as below.
Some other options like spout and plastic handle, that may have influence on the sizes that is needed to hold certain volume, for example a 16mm spout will take less space than a 33mm spout on standup doypack, and relative it may requires a smaller pouch to hold certain volume of products.
you may read some posts here regarding the influence of spout and plastic handle on the pouch sizes.