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Does tablet thickness affect hardness?

Q: Does tablet width and thickness affect tablet hardness? What other factors can influence this?

A: Fred Rowley responds:

This is a complex question to answer correctly. To a certain degree, tablet width and thickness do affect tablet hardness. Before answering the question directly, it is most important to recognize that tablet hardness is a function, not a set point on a tablet press. There is no “tablet hardness” control on a tablet press either. Tablet press speed, granulation flow, air in the powder, the failure to get the air out of the powder, and the speed of the force feeder wheels all can potentially affect tablet hardness.

Depending upon the nature of the active ingredient and the quantity of the ingredient in the tablet, the tablet may also vary in hardness. But with a known formulation in a specific tablet shape, with all other factors considered constant, a variation in thickness will produce a corresponding change in tablet hardness. Again, this is not a one-to-one ratio. Sometimes it takes a significant change in thickness before one sees a hardness response.