How to Calculate Fence Materials
Building a fence requires precise math to ensure you don't end up with half a panel left over at the end of your property line. Our calculator determines your exact post and panel count, and then uses advanced cylindrical geometry to tell you exactly how many 80lb bags of concrete you need to set your posts.
The Concrete Math (Post Hole Geometry)
Most generic calculators just guess "2 bags per post." But a 3-foot deep hole requires significantly more concrete than a 1.5-foot hole. We calculate the exact volume of a standard 10-inch diameter hole, subtract the volume of the 4x4 post (which actually measures 3.5" x 3.5"), and divide by 0.60 cubic feet (the yield of one 80lb bag of concrete).
Frequently Asked Questions
How deep should fence post holes be?
As a general rule, post holes should be 1/3 to 1/2 the height of the above-ground fence. For a 6-foot tall fence, dig your holes at least 2 to 3 feet deep.
Do I need gravel at the bottom of the post hole?
Yes, adding 6 inches of gravel at the bottom of the hole before setting the post improves drainage and prevents the bottom of the wood post from rotting.
How much does a full fence cost compared to just materials?
See our Fence Cost Guide for a full 10-year cost comparison across wood, chain-link, vinyl, and aluminum, including maintenance costs most people forget to budget for.