Concrete Footing Calculator
Strip footing or pad — pick the project, then enter the trench or pad size.
This footing is about a cubic yard or more. A ready-mix truck is usually easier than mixing that many bags by hand.
How the numbers are figured
A strip footing is a long rectangular trench: run × width × depth, with width and depth converted from inches to feet. A pad is a short rectangle under a point load, using length × width × depth. Divide cubic feet by 27 for cubic yards. Bags use standard US pre-mix yields and round up.
Common questions
How do you calculate concrete for a strip footing?
Multiply the run in feet by the width in feet and the depth in feet. Width and depth are usually measured in inches, so divide each by 12 first. Divide cubic feet by 27 for cubic yards.
What is the difference between a strip footing and a pad?
A strip footing is a long trench under a wall. A pad is a square or rectangle under a post or point load. Pick the matching project in the menu. The math is volume either way.
How many 80 lb bags for a 20 foot footing?
A 20 foot run that is 16 inches wide and 8 inches deep is about 17.8 cubic feet, or 30 bags of 80 lb mix, before waste. With 10% extra, plan on 33 bags.