Concrete Block Calculator
Building a block wall? Enter the wall length and height to get the number of standard 8×8×16 blocks (plus a mortar note) — a concrete wall calculator for garden walls, foundations, and sheds. Switch tabs for ready-mix bag counts for slabs and driveways, or the sonotube calculator that answers how many bags of concrete per fence post.
Frequently Asked Questions
How does the concrete block calculator work?
A standard 8×8×16 block covers about 0.89 square feet of wall face including the mortar joint, so the calculator divides your wall's square footage by that and adds a 5% waste allowance. The result assumes a single-wythe (one block thick) wall.
How many bags of concrete per fence post do I need?
A typical 4×4 post in a 10-inch diameter hole 2 feet deep needs about 1.6 cubic feet of concrete — roughly two 80-lb bags or three 60-lb bags. Use the Sonotube tab with your exact hole diameter and depth for a precise count.
What is a sonotube calculator?
A sonotube is a round cardboard form used to cast concrete footings and piers. The calculator treats each hole as a cylinder (π × radius² × depth), converts to cubic feet, then tells you how many 60-lb or 80-lb ready-mix bags that equals.
Can I use this as a concrete driveway calculator?
Yes — use the Ready-mix Bags tab. Enter the driveway length, width, and thickness (usually 4 inches = 0.33 ft) plus a waste factor, and it converts the volume to 60-lb and 80-lb bags, rounded up.