Enter your footing dimensions and quantity — get bag counts, cubic yards, and a cost estimate instantly.
Based on standard industry formulas used by contractors and material suppliers
Enter Footing Details
Quick Presets
in
in
in
in
in
%
Prices vary by location. Enter your local supplier rates.
Your Footing Estimate
Total Concrete Needed
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cubic yards of concrete
Total Volume
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cubic feet
60 lb Bags
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bags (inc. waste)
80 lb Bags
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bags (inc. waste)
Cost Breakdown
60 lb Bags
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80 lb Bags
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Ready-Mix
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Note your quantities before purchasing — prices and availability vary by supplier.
Example Calculation
Here is a step-by-step walkthrough for 4 round deck footings, each 12 inches in diameter and 36 inches deep — one of the most common residential footing setups.
4 × round footings — 12 in diameter, 36 in deep
Step 1 — Radius12 in ÷ 2 = 6 in = 0.5 ft
Step 2 — Single Volumeπ × 0.5² × 3 ft = 2.36 cu ft
Step 3 — All Footings2.36 × 4 = 9.42 cu ft
Step 4 — Add 10% Waste9.42 × 1.10 = 10.36 cu ft
Step 5 — Cubic Yards10.36 ÷ 27 = 0.38 cu yd
Step 6 — 60 lb Bags10.36 ÷ 0.45 = 24 bags
How This Calculator Works
The calculator computes the volume of each footing based on its shape: round footings use π × r² × depth; square footings use side² × depth; rectangular footings use length × width × depth. It then multiplies by your footing count and adds a waste factor.
Volume is then converted to cubic yards and split into bag counts for both 60 lb and 80 lb mixes. Cost estimates multiply bag count or cubic yards by your supplied prices.
Pro tip: For footings under 1 cubic yard total, bagged concrete with tube forms (Sonotubes) is the standard approach. For large projects with many footings, a ready-mix order may save significant time and cost.
Practical Tips for Concrete Footings
Dig below the frost line. In cold climates, footings above the frost line will heave, crack, and shift. Check your local code — frost depth ranges from 12 inches in the South to 48 inches or more in the northern US and Canada.
Use Sonotube (tube form) for round footings. Cardboard tube forms keep the shape, reduce blowouts, and make it easy to pour by yourself. Available at any hardware store, they're cheap and well worth it.
Set anchor bolts or post bases while wet. If you're setting hardware into the footing, place it while the concrete is still fluid. Use a level and a template to ensure correct spacing.
Let it cure before loading. Wait at least 24–48 hours before placing posts or any load. Full cure strength takes 28 days — but 7 days is enough for light construction activity.
Don't add extra water to the mix. It might seem easier to pour but it weakens the concrete significantly. Follow bag instructions exactly.
Always round up bag counts. You can't pause mid-pour. Order one or two extra bags and return what you don't use.
Common Mistakes to Avoid
Footings too shallow. The most common and costly error. A footing above the frost line will shift seasonally, causing structural problems that are expensive to fix.
Wrong diameter. Undersized footings can't spread the load and may punch through soft soil. Use the rule of thumb: footing diameter = 3× the post width, then verify with your local code.
Skipping the gravel base. Pouring directly onto soft or wet soil leads to settlement. Place 4–6 inches of compacted gravel first to provide drainage and a stable base.
Unit confusion. This calculator accepts diameter and depth in inches (converted internally). Make sure you're not mixing feet and inches in your inputs.
Assumptions
◦Concrete yield: 60 lb bags = 0.45 cu ft; 80 lb bags = 0.60 cu ft. Standard manufacturer figures.
◦Waste factor: Default 10% covers spillage and tube overfill. Increase to 15% for difficult pours or irregular excavations.
◦Round footing formula: π × r² × depth, where r = diameter ÷ 2. All dimensions converted to feet before calculation.
◦Prices vary: Bag and ready-mix prices vary by region and season. Update the input fields to match your local supplier pricing.
◦Results are estimates: Always confirm quantities with your supplier before ordering. Field conditions may vary.
Frequently Asked Questions
Footings must extend below the local frost line. In the southern US, this can be as shallow as 12 inches. In the midwest and northeast, expect 36–48 inches. In Canada, 48–60 inches is common. Check with your local building department — undersized depth is the number one reason footings fail.
The general rule is three times the post width. For a 4×4 post (3.5 inches actual), use a 12-inch footing. For a 6×6 post (5.5 inches), use at least an 18-inch footing. Verify against your local span tables and the load your deck will carry — heavier decks with more span need larger footings.
Fast-setting concrete (like Quikrete Fast-Setting) is excellent for post footings — you can set a post and have it stable in 20–40 minutes. However, it costs more per bag and must be poured dry into the hole with water added on top. For large or structural footings, standard mix with a full 28-day cure is the better choice.
For simple post footings supporting a deck or fence, rebar is usually optional — the footing just needs to resist compression. For structural footings (bearing walls, columns, heavy loads), two or three pieces of vertical rebar tied to horizontal rebar is typically required. Check your local code and structural drawings.
Standard concrete reaches initial set in 24–48 hours. You can attach posts and begin light framing after 3–7 days. Full structural strength takes 28 days. In cold weather (below 40°F / 5°C), curing slows dramatically — use insulated blankets or cold-weather concrete additives to protect the pour.
It depends entirely on the footing size. A 60 lb bag yields 0.45 cubic feet. A 12-inch round footing at 36 inches deep needs about 2.36 cubic feet — roughly 6 bags. A smaller 10-inch round at 24 inches deep needs 1.09 cubic feet — about 3 bags. Use the calculator above to get exact counts for your specific dimensions.