The bags of mulch can come in variant sizes. Usually, towards the bottom of the front or sometimes the upper-right corner, on the bag there is a specification on how many feet by however many feet that bag covers.
Usually if you read on the back of the mulch bag it will tell how much square footage each bag wil cover and then you just need to figure out the square footage you need it for and you will know how much mulch you will need to buy for youe project.
One bag per tree is a good start for mulching the trees. Larger fruit trees will need up to four bags. For bushes one bag per three foot is a base. More depth requires more bags.
