A yoga block can be used at three different heights to accommodate you in different poses, to use as you progress in flexibility, or to use at varying heights to increase the intensity of a pose. This is why blocks are a helpful and versatile prop.
These blocks are 4″ x 6″ x 9″. So as the picture shows you can use the blocks on each side: on the wide flat side, on it’s long edge, or on it’s short edge. When using a block on it’s tallest side, you may find that the 4″ block will feel more stable (than a 3″x6″x9″ block) because of it’s wider base. But if you have been practicing for awhile and feel confident in your balance, a 3″ block works just fine.