A good way to make sure they'll fit is to bring your container with you to the nursery or bring measurements.
When selecting plants for your terrarium, size is of utmost importance, depending on the dimensions of your container. Be sure to buy plants that are small enough to fit into your terrarium container, preferably without touching the sides of the glass. A good way to make sure they'll fit is to bring your container with you to the nursery or bring measurements.