More than you think. I know, that doesn’t help you much but it’s actually an important fact to remember. You always need more stones than you think. The more stones you have to choose from, the easier it will be to find the stone you’re looking for when you start building your stone wall.
For a more exact answer, we can use a simple formula. Stones, like many building materials, are often measured in cubic yards. Stones can also be measured and sold by the ton. Follow these steps for determining how much stone you need to build a stone wall.
(L'xW'xH') / 27 = cubic yards of stone needed
So, if you’re building a stone wall that is 20 feet long, 2 feet wide and 3 feet high, you would use the formula like this:
20’x2’x3’ = 120
120/27 = 4.44 cubic yards of stone
You would need a little less than 4 ½ yards of stone to build your stone wall. I would recommend getting at least five yards. If you can afford it, get six or seven yards. When you’re building the wall, you’ll be thankful to have the stones to choose from.
Some places sell stone by the ton. To determine how many tons of stone you need to build your stone wall, simply multiply the number of yards by 1.5.
4.44 x 1.5 = 6.66 tons of stone
Again, you’ll want to round up.