How do you calculate concrete for a footing?

Use the actual footing geometry first. Rectangular footing volume is length times width times footing depth, and round footing volume is pi times radius squared times footing depth.

Is this calculator good for deck footings?

Yes. It is a strong fit for deck-footing quantity planning once you already know whether the footing is round or rectangular and what footing depth you need to estimate.

Does this calculator tell me footing size, spacing, or reinforcement?

No. This page estimates concrete quantity after the footing geometry is known. It does not determine footing width, spacing, reinforcement, or structural design choices.

Concrete Footing Calculator

Estimate cubic yards, total weight, and 40/60/80-lb bag counts for rectangular, round, and deck footing pours in one footing-first workflow.

Choose shape

Used to calculate volume & materials.

Editing Section 1

Update dimensions. Results update only after Calculate.

Edited

Length

Width

Footing Depth

Quantity

Waste Control

Suggested 10 percent, adjust as needed.

10%

Preview

1/1 Free DailyWireframeAI Style

Results Card

Results update when you press Calculate.

Press Calculate to see results.

Calculation Details

Why this footing calculator is more useful than forcing footing intent into slab or column pages

Footing queries often split in two directions: rectangular and square support pads on one side, and round deck or post-support footings on the other. What people usually want is simple quantity math for the actual footing geometry, not a generic slab estimator and not a taller pier workflow. This page keeps those footing-specific checks next to the live calculator.

Keep footing language footing-specific

The page uses footing depth, rectangular footing, and round footing terminology instead of making every support job look like a slab or a freestanding column.

Absorb deck-footing and square-footing intent in one place

The reference tables and FAQ help catch the query variants that usually wrap around the same concrete-volume problem.

Answer quantity questions without overpromising design guidance

This page estimates material quantity well. It does not pretend to size footing width, spacing, reinforcement, or load capacity from search intent alone.

Point users to slab, pad, or column only when the geometry actually changes

If the job is a broad flat pour, a small rectangular equipment pad, or a taller cylindrical pier, the page sends people to the matching calculator instead of stretching footing math too far.

Reference Tables

Common Footing Sizes, Bag Yield, and Query-Boundary Checks

Use these tables as quick planning references for common footing dimensions and the query variants that usually map to this page. Final footing size, bearing width, spacing, and reinforcement decisions still belong to the actual project.

Common rectangular footing starting points

These rows are fast rectangular checks for small support footings and simple base planning.

Footing

2 ft × 2 ft × 12 in

Base volume: 0.15 yd³
80-lb bags: Approx. 7 bags
Planning note: Useful baseline for small isolated support footings where rectangular geometry is already known.

Footing

3 ft × 3 ft × 12 in

Base volume: 0.33 yd³
80-lb bags: Approx. 15 bags
Planning note: Shows how quickly bag count rises once footing width expands even when depth stays the same.

Footing

2 ft × 4 ft × 12 in

Base volume: 0.30 yd³
80-lb bags: Approx. 14 bags
Planning note: Helpful when the support footprint is rectangular rather than square.

Footing	Base volume	80-lb bags	Planning note
2 ft × 2 ft × 12 in	0.15 yd³	Approx. 7 bags	Useful baseline for small isolated support footings where rectangular geometry is already known.
3 ft × 3 ft × 12 in	0.33 yd³	Approx. 15 bags	Shows how quickly bag count rises once footing width expands even when depth stays the same.
2 ft × 4 ft × 12 in	0.30 yd³	Approx. 14 bags	Helpful when the support footprint is rectangular rather than square.

Rounded values use the same calculator assumptions as the live workflow and do not include extra waste.

Common round footing starting points

These rows help with deck-footing and round-support estimates where diameter and footing depth drive the order.

Footing

12 in × 12 in

Base volume: 0.03 yd³
80-lb bags: Approx. 2 bags
Planning note: Small round footing baseline for light-support scenarios and quick deck-post checks.

Footing

18 in × 12 in

Base volume: 0.07 yd³
80-lb bags: Approx. 3 bags
Planning note: A practical midpoint when the footing grows beyond a very small deck-post assumption.

Footing

24 in × 12 in

Base volume: 0.12 yd³
80-lb bags: Approx. 6 bags
Planning note: Useful for comparing a broader round footing against rectangular alternatives.

Footing	Base volume	80-lb bags	Planning note
12 in × 12 in	0.03 yd³	Approx. 2 bags	Small round footing baseline for light-support scenarios and quick deck-post checks.
18 in × 12 in	0.07 yd³	Approx. 3 bags	A practical midpoint when the footing grows beyond a very small deck-post assumption.
24 in × 12 in	0.12 yd³	Approx. 6 bags	Useful for comparing a broader round footing against rectangular alternatives.

Rows assume a simple round footing cylinder. Bell-outs, stepped bases, and mixed-depth excavation should be run through the full calculator.

What the main footing query variants usually mean

These are often the same quantity problem wrapped in different project language. The biggest risk is using the wrong geometry or assuming this page sizes the structure for you.

Query

Deck footing calculator

Usually means: Round or isolated support footings under deck posts where diameter and footing depth matter more than broad slab area.
Check before ordering: Confirm whether the footing is actually round, how many repeated footings you have, and whether depth is controlled by site requirements.

Query

Square footing calculator

Usually means: Rectangular footing math where length and width happen to match.
Check before ordering: Use the rectangular footing mode and enter the actual square footprint plus footing depth.

Query

Spread or strip footing calculator

Usually means: Foundation-support intent where this page can help with volume, but not with final footing sizing logic.
Check before ordering: Use the calculator for quantity only after the actual footing dimensions are known.

Query

Footing size or spacing calculator

Usually means: A design question, not just a quantity question.
Check before ordering: This page estimates concrete volume once geometry is known. It does not determine footing width, spacing, reinforcement, or load capacity.

Query	Usually means	Check before ordering
Deck footing calculator	Round or isolated support footings under deck posts where diameter and footing depth matter more than broad slab area.	Confirm whether the footing is actually round, how many repeated footings you have, and whether depth is controlled by site requirements.
Square footing calculator	Rectangular footing math where length and width happen to match.	Use the rectangular footing mode and enter the actual square footprint plus footing depth.
Spread or strip footing calculator	Foundation-support intent where this page can help with volume, but not with final footing sizing logic.	Use the calculator for quantity only after the actual footing dimensions are known.
Footing size or spacing calculator	A design question, not just a quantity question.	This page estimates concrete volume once geometry is known. It does not determine footing width, spacing, reinforcement, or load capacity.

Footing keywords overlap heavily. The safest boundary is simple: use this page for concrete quantity after the footing geometry is known.

Need a broader patio, walkway, or driveway workflow instead? Switch to the slab calculator. For small rectangular support bases, use the pad calculator. For taller cylindrical pours, use the column calculator.

Worked Examples

Footing examples that match the main search variants

These examples keep the quantity math visible while staying inside the page boundary: concrete volume first, then waste, bag counts, and context.

Example 1

2×2 rectangular footing at 12 inches

A clean baseline for small rectangular support-footing planning where the footprint is already known.

Base volume

0.15 yd³

With 10% waste

0.16 yd³

80-lb bags

Approx. 7 bags

Geometry

Rectangular footing

1Length × width × footing depth = 2 × 2 × 1 = 4 cubic feet.
2Base volume = 4 ft³ = 0.15 yd³.
3Add 10% waste to land at about 0.16 yd³.
4Using the page's 0.60 ft³ yield for an 80-lb bag, that lands at roughly 7 bags.

Takeaway: This is small enough to stay practical with bagged concrete, but it still benefits from locking the footing depth before you count bags.

Example 2

24-inch round footing at 12 inches

A round-footing example that shows how diameter alone can move the order faster than many people expect.

Base volume

0.12 yd³

With 10% waste

0.13 yd³

80-lb bags

Approx. 6 bags

Geometry

Round footing

1Radius = 24 in ÷ 2 = 12 in = 1 ft.
2Base volume = pi × 1² × 1 = 3.14 ft³ = 0.12 yd³.
3Add 10% waste to reach about 0.13 yd³.
4That works out to roughly 6 80-lb bags with the calculator's default bag yield.

Takeaway: Round footing jobs stay compact on paper, but bag counts still rise quickly once diameter grows.

Example 3

12-inch round deck footing at 36 inches

This is the deck-footing scenario where the diameter looks small, but the depth keeps the order honest.

Base volume

0.09 yd³

With 10% waste

0.10 yd³

80-lb bags

Approx. 5 bags

Query match

Deck footing

1Radius = 12 in ÷ 2 = 6 in = 0.5 ft.
2Footing depth = 36 in = 3 ft.
3Base volume = pi × 0.5² × 3 = 2.36 ft³ = 0.09 yd³.
4Add 10% waste to land at about 0.10 yd³, or roughly 5 80-lb bags.

Takeaway: Even a small deck footing should be sized by real depth, not by diameter alone.

Common Mistakes

Where footing estimates usually go wrong

The math itself is straightforward. Most footing mistakes come from using the wrong geometry, confusing quantity with design, or letting diameter and depth assumptions drift apart.

Mistake 1

Using slab language when the job is really a footing

A footing is still concrete volume, but the planning context is different from a broad flat pour.

Rectangular footings and round footings need footing depth, not a generic slab story.
Deck-footing intent is usually about isolated support geometry, not patio square footage.

That is why this page starts with footing geometry first.

Mistake 2

Letting the quantity calculator answer design questions it cannot answer

Search intent often blends concrete volume with footing sizing, spacing, and load capacity. Those are not the same job.

This page can estimate concrete quantity once the footing dimensions are known.
It does not determine footing width, spacing, reinforcement, frost protection, or bearing design.

Keep quantity planning and structural decisions in separate buckets.

Mistake 3

Ignoring repeated footing counts until the end

One footing may look small, but multiple identical supports stack quickly into a real material order.

Count repeated deck or support footings early so the total is visible.
Apply waste after the full repeated quantity is known.

That keeps the order-ready number from drifting late in the process.

Mistake 4

Using the footing page when the job is really a pad or a taller pier

This page is for footing quantity. Other support shapes still deserve their own geometry when the project intent changes.

Use the pad calculator for small rectangular equipment or AC bases.
Use the column calculator when the pour is really a taller cylindrical pier or sonotube.

Matching the calculator to the real geometry is still one of the fastest ways to avoid a bad order.