Please note: For your convenience, this calculation has been rounded up slightly.
Important reminder: Every effort has been made to ensure the accuracy of this calculation. But before purchasing materials for any project, please check amounts with your suppliers or contractors.
Don't attempt to dig post holes with a spade or shovel; it will be very difficult to go deep enough. To dig by hand, use a clamshell or twist-type posthole digger. Digging can be very hard work, especially if you are out of shape and the ground is full of rocks or roots. Take it easy, or you could seriously damage your lower back.
A few tips: If you have many holes to dig, rent a power auger, and use it with a helper; a rental center will show you how. Better yet, hire a landscaping company to dig the holes for you. Once the hole is dug, shovel in a few inches of gravel, so water can drain away from the bottom of the post.
Post holes are not precise in size (especially if dug by hand), so the following calculations are estimates. These calculations presume that you will set a 4x4 post, which measures 3 1/2" x 3 1/2." Purchase bags of ready-mix concrete. Pour the dry mix into a wheelbarrow and slowly add water, all the time stirring and shoveling with a hoe, until the mixture is just loose enough to pour.