🧱 Sonotube Calculator
Find out how much concrete you need to fill round Sonotube forms for deck footings or posts, based on diameter, height, and quantity.
What this calculator does
The Sonotube calculator finds how much concrete is needed to fill one or more round cardboard concrete forms (commonly sold under the brand name Sonotube) used for deck footings or fence posts.
The formula
The volume of a cylinder is pi times radius squared times height. The calculator converts your tube diameter to feet, finds the radius, and multiplies by height and quantity to get total cubic feet, which is then converted to cubic yards. Bag count is estimated using the common yield of an 80 lb bag of concrete mix, which produces about 0.6 cubic feet of concrete.
This is a general planning estimate. Always round up slightly and check the yield printed on your specific bag of concrete mix, since yields vary by brand.