How the math works
A footing is a long rectangular trench. Volume is length × width × depth. Contractors quote width and depth in inches — a “16-inch wide by 8-inch deep” footing is standard for residential — so we convert both to feet before multiplying and then divide by 27 to get cubic yards.
The waste factor (default 10%) accounts for over-dig — real trenches are never as clean as the dimensions on paper.
When to order ready-mix vs. bags
Even short footings add up fast — a 40-foot foundation footing at 16″ × 8″ is over 1.3 cubic yards. That’s 60+ bags of 80-lb premix, mixed by hand, poured in sequence before the first section starts curing. For anything past a few short piers, delivered ready-mix wins on speed and consistency.
Bags stay competitive only for very short runs — a single pier, a deck post footing, or a repair. Once you cross the local short-load threshold the fee cancels the small-pour savings.
Getting a real quote
Defaults here are national ballparks. Local ready-mix pricing swings with fuel, cement, and delivery distance. Call your closest producer once you have your yardage; most will quote firm over the phone.