WooCommerce Advanced Quantity:
The WooCommerce Advanced Quantity plugin lets you control how the quantity field for products is working.
Right now (v. 1.5.6) you can change the minimum value of the quantity field, you can set a maximum value, you can change the interval between each step in the quantity field, you can set a standard value for the quantity fields and you can add a price suffix.
This gives you a lot of possibilities to control the quantity of each product that a customer can buy. Proudly made by Morning Train.