While I have locked hair as short as 5cm, I’ve found that the minimum hair length for dreadlocks is around 15cm. Good hair length for dreads starts at around 40cm but that can take quite some time to achieve if you have short hair that doesn’t grow fast. Length of hair for dreadlocks when you plan to add extensions should be again a minimum of 15cm. While some people think the best hair length for dreadlocks is super long just remember it will take a lot more time to dread your hair when you have massive length.