Concrete Footing Calculator
Calculate cubic yards, bag count, and cost for round piers (Sonotube) or rectangular footings — with waste factor and ready-mix vs. bags comparison.
| Metric | Value |
|---|
Related Tools
Concrete Footing Calculator: How to Calculate Concrete for Footings
A concrete footing calculator takes the guesswork out of one of construction's most critical steps — estimating how much concrete you need for your footings. Whether you're pouring round piers for a deck or rectangular spread footings for a foundation, getting the volume right prevents costly overorders and dangerous underorders. This free concrete yard estimator handles both footing shapes, applies a waste factor, and converts cubic feet to cubic yards and bag counts automatically.
Getting your footing concrete right matters more than almost any other part of a build. Footings transfer structural loads to the ground, and both undersized and over-poured footings can cause long-term problems. Use the calculator above before placing any order.
How the Formulas Work
The calculator uses two geometry formulas based on footing shape:
where r = diameter (in) ÷ 24
Rectangular: V (cu ft) = length (ft) × width (ft) × depth (ft)
Total Volume (yd³) = V (cu ft) × quantity ÷ 27
With Waste = Total yd³ × (1 + waste% ÷ 100)
Bags Needed = ⌈ V cu ft × (1 + waste%) ÷ bag yield ⌉
The conversion factor 27 converts cubic feet to cubic yards (1 yd³ = 27 cu ft). The ceiling function on bags ensures you always round up — you can't buy a fraction of a bag.
Understanding Waste Factor
Concrete waste happens even on the most carefully managed jobs. Overdig in the form, spillage during pouring, residual concrete in the mixer drum, and slight form bulge all consume more material than the theoretical volume. Most professionals add 10% waste for footings — some increase to 15% for very deep pours or rough-cut forms.
Never skip the waste factor when ordering ready-mix. Trucks cannot easily return with a second load if you run short, and leftover concrete in the drum is charged at the full yard rate. Order with waste; use what you need.
Ready-Mix vs Bags: Which Should You Choose?
For volumes under 1 cubic yard, bagged concrete is almost always cheaper and more practical. You avoid the ready-mix truck's minimum charge (typically 1 yd³), delivery fee, and fuel surcharge. Above 1 yard, ready-mix becomes competitive — and above 3–4 yards, it's usually significantly cheaper per cubic yard than buying bags.
Beyond cost, consider logistics: mixing 40+ bags by hand is exhausting and time-consuming. If the calculator shows more than 40 bags, strongly consider a ready-mix delivery even if cost is similar. The labor savings alone justify it on most projects.
Pier Size Reference Table
Use this quick-reference table for common Sonotube sizes at standard depths. Bag counts shown are without waste factor; add 10% for your actual order.
| Pier Diameter | Depth | Vol / Pier (cu ft) | Yards / Pier | 80lb Bags / Pier* |
|---|---|---|---|---|
| 6 in | 3 ft | 0.589 | 0.022 | 1 |
| 8 in | 3 ft | 1.047 | 0.039 | 2 |
| 10 in | 3 ft | 1.636 | 0.061 | 3 |
| 12 in | 4 ft | 3.142 | 0.116 | 6 |
| 14 in | 4 ft | 4.276 | 0.158 | 8 |
| 16 in | 4 ft | 5.585 | 0.207 | 10 |
| 18 in | 5 ft | 8.836 | 0.327 | 15 |
| 24 in | 5 ft | 15.708 | 0.582 | 27 |
* Bags = ⌈cu ft ÷ 0.60⌉ without waste. Add 10% to your final order.
Tips for Ordering Concrete
- Always add waste: 10% is standard for footings; increase to 15% for rough or irregular forms.
- Ready-mix minimum: Most suppliers charge for a minimum of 1 cubic yard. If your project is under that, bags save money.
- Order time: Ready-mix trucks need 24–48 hours notice in most markets; popular times book out further.
- Short load fee: Ordering less than a full drum (typically 8–10 yd³) often triggers a short-load surcharge of $50–$150.
- Curing time: Footings need at least 24–48 hours at 50°F+ before loading. In cold weather, plan for blankets or heated enclosures.
- Check local frost depth: Footing depth requirements vary by climate zone. In northern states, footings must extend below the frost line (often 36–48 inches).
- Slump matters: Specify slump (workability) when ordering ready-mix. A 4-inch slump is typical for footings; don't let the driver add excess water.