I'll take a shot at it explaining it and maybe save a visitor a lot of reading.
To calculate mulch you need to know 2 things.
How big is the area and how deep do you want it.
area = length x width.
dont get hung up on odd shapes. Box it out in sections.
If it's a triangle do lxw and divide it in half. add all those up.
Depth I usually do 3 inches of shredded mulch. I never use bark.
3 inches is a fraction of 1 foot or 3/12.
to multiply using a fraction you have to convert it to a decimal. so 3 divided by twelve is (.25). 4 divided by 12 is (.33)
so now you have your area 65ft x 6ft = 390 sqft.
I'd round that up to 400sgft of area you want to mulch.
If you want 3 inches in that area
400 x .25 (3/12) = 100
thats your cubic feet. Now you want to convert it to yards.
100/27 = 3.7 yards of mulch
round that up to 4 yards.
I pay about 25.00 per yard. I can put that on a 16" trailer with a tarp. or you could have it delivered.
I charge 65.00 per yard.
That how you do it in bulk. I you want to use bags you can still charge the same but it will cost you more for supplies. I hardly ever bag.
If you use bags don't do the last step where you divide by 27.
Just divide by the number of feet listed on the bag. The big bags are 3 feet and the smaller home depot bags are 2 feet.
so 100 / 3 = 33.3 you need 34 big bags.
It really simple but if your new to it,it's easy to forget.