Ideally, you should layer bark chippings 2cm thick to stop weeds from growing. A 50L bag of bark chippings will cover 2m2.
Bark chippings are effective for weed control, as they block the sunlight that weeds need to grow. Bark chippings can also help retain moisture and protect plant roots, as well as look aesthetic in your bed display.
Other weed control measures are available, such as weed control fabric and weed killers.