Commerce minimum quantity and purchase multiplier I have added a field to content type Product with the purchase quantity (default 1). Products can only be purchased by this quantity. For example, if its value is 5, you could buy 5, 10, 15, and so on. This is configured by products, and some products could have a value of 1, and others could have a value greater than 1.
After read some post about "quantities" and "minimum quantity", I haven't found how to do it. I have tried with some modules like Commerce Extras, and Commerce Add to Cart Extras. But without success.
Could some one give me some ideas how to do it?
Thanks in advance.
Ryan's answer on this question is the approach you'd want to take: 


Install Commerce Custom Product.
Create a new line item type that has new quantity select field and widget. Expose this to the add to cart form.
Hide the regular quantity selection to the add to cart form.
Use a rule to take the value in the field you created in step 2 and set the quantity field to that value on the line item.