Stand-up pouches are measured as Width (W) x Length (L) x Gusset (G).
Lay-flat pouches are measured as Width (W) x Length (L).
The closure is always located along the top (width) dimension.
When determining the size you need for your product type, consider that space is needed below the closure to allow for it to remain secure. The amount of space needed will vary by the type and weight of product in the pouch. There are, unfortunately, no hard and fast rules for this, so we suggest that you test and judge based on similar pouches and products in your industry.