You're in for a shock. Our 7 4' deep holes took **42** 80 pound bags of
quickcrete.

This is one of the many reasons to do the math ahead of time and get stuff
delivered. I've seen people nearly destroy their vehicle cramming a ton of
bricks into the trunk when they could've just gotten an entire palette
delivered for around $50. Likewise with concrete and gravel, check with a
local supplier. You can get gravel for about a THIRD of what bagged stuff
from the box stores would gouge you.

Renting a mixer for concrete is about the only way to go unless you've got
enough to justify ordering up some delivered by mixer truck. Then it's one
wheelbarrow at a time to offload it from the hopper to the holes. And
you're generally stuck with ALL that came in the load, not just the amount
you need. So unless you've got a lotta holes, patio and/or stairway
landings then mixing your own is the way to go. Just buy it from a bulk
source and have it delivered instead of overpaying the home despot and
wrecking the car.