Concrete Footing Calculator

Concrete Footing Calculator: Estimate Concrete for Footings, Footers, and Foundations

Use this concrete footing calculator to estimate how much concrete you need for footings, footers, piers, posts, columns, foundation walls, and similar concrete support structures.

Footings are the base that helps transfer the weight of a structure into the ground. They may support a deck, porch, gazebo, garage, house foundation, retaining wall, shed, column, or post. Because footings are usually buried, it is important to estimate the concrete correctly before pouring.

This guide explains how to calculate concrete for footings, how many bags you may need, how footing size affects concrete volume, and how to estimate footing cost without overcomplicating the math.

What Is a Concrete Footing Calculator?

A concrete footing calculator estimates the amount of concrete needed for a footing based on its shape and dimensions.

Most footings are calculated using:

• Length
• Width
• Depth
• Quantity
• Concrete price
• Bag size, if using ready-mix bags

The calculator gives the result in cubic feet, cubic yards, or concrete bags. Concrete is commonly ordered by volume, especially in cubic yards for ready-mix delivery. SRM’s footing calculator also notes that concrete is ordered by volume in cubic yards.

A footing calculator is useful for:

• Square footings
• Rectangular footings
• Continuous footings
• Strip footings
• Round footings
• Pier footings
• Column footings
• Foundation footings
• Gazebo footings
• Deck footings

How to Calculate Concrete Footings

The basic formula for a rectangular concrete footing is:

Length × width × depth = concrete volume

If your measurements are in feet, the result is cubic feet.

To convert cubic feet to cubic yards:

Cubic feet ÷ 27 = cubic yards

Example:

A footing is:

• 10 feet long
• 2 feet wide
• 1 foot deep

Concrete volume:

10 × 2 × 1 = 20 cubic feet

Convert to cubic yards:

20 ÷ 27 = 0.74 cubic yards

So, this footing needs about 0.74 cubic yards of concrete before adding waste.

Concrete Footing Formula

For rectangular or square footings:

Cubic yards = length × width × depth ÷ 27

For round concrete footings:

Cubic yards = 3.1416 × radius² × depth ÷ 27

Inch Calculator uses the same general approach: rectangular footing volume is length × width × depth divided by 27, while round footing volume uses radius squared × depth × pi divided by 27.

Concrete Footing Calculator Table

Here are simple examples for common rectangular footings.

These are clean volume estimates. Real projects should include extra concrete for uneven excavation, spillage, and form variations.

How Much Concrete Do I Need for Footings?

To find out how much concrete you need for footings, measure the footing size and multiply:

Length × width × depth

Then multiply by the number of footings.

Example:

You have 6 footings. Each footing is 2 ft × 2 ft × 1 ft.

One footing:

2 × 2 × 1 = 4 cubic feet

Six footings:

4 × 6 = 24 cubic feet

Convert to cubic yards:

24 ÷ 27 = 0.89 cubic yards

Add 10% waste:

0.89 × 1.10 = 0.98 cubic yards

You should plan for about 1 cubic yard of concrete.

Why Add Extra Concrete?

Concrete estimates should not be too tight. Footing holes are rarely perfect. Some may be wider, deeper, or uneven at the bottom.

A good rule is to add 10% to 15% extra concrete. Inch Calculator also recommends ordering 10% to 15% additional material for footings because digging can create voids or slightly deeper areas.

Add extra concrete for:

• Uneven excavation
• Slightly oversized holes
• Spillage
• Forms not matching exact dimensions
• Rough soil conditions
• Waste during placement

Running short during a footing pour is not fun. Concrete waits for nobody.

Square Footing Concrete Calculator

For a square footing, use:

Side × side × depth

Example:

A 24 inch by 24 inch footing that is 12 inches deep:

Convert to feet:

• 24 inches = 2 ft
• 12 inches = 1 ft

Volume:

2 × 2 × 1 = 4 cubic feet

Convert to cubic yards:

4 ÷ 27 = 0.148 cubic yards

So, one 24 × 24 × 12 inch footing needs about 0.15 cubic yards of concrete.

Rectangular Footing Calculator

For a rectangular footing, use:

Length × width × depth

Example:

A continuous footing is:

• 30 ft long
• 18 in wide
• 12 in deep

Convert inches to feet:

• 18 in = 1.5 ft
• 12 in = 1 ft

Volume:

30 × 1.5 × 1 = 45 cubic feet

Convert to cubic yards:

45 ÷ 27 = 1.67 cubic yards

Add 10% waste:

1.67 × 1.10 = 1.84 cubic yards

You would order about 1.85 cubic yards.

Round Concrete Footing Calculator

Round footings are common for deck posts, pergolas, fence posts, columns, and gazebo footings.

Formula:

3.1416 × radius² × depth = cubic feet

Then divide by 27 for cubic yards.

Example:

A round footing is:

• 18 inches diameter
• 36 inches deep

Convert to feet:

• Diameter = 1.5 ft
• Radius = 0.75 ft
• Depth = 3 ft

Volume:

3.1416 × 0.75² × 3 = 5.30 cubic feet

Convert to cubic yards:

5.30 ÷ 27 = 0.20 cubic yards

So, one round footing needs about 0.20 cubic yards of concrete before waste.

Column Footing Calculator

A column footing calculator is useful when estimating concrete for posts, piers, columns, and isolated pad footings.

Column footings may be:

• Square
• Rectangular
• Round
• Bell-shaped
• Pier-style

For a square or rectangular column footing, use the standard footing formula. For a round pier, use the circular formula.

If the footing has a bell-shaped base, the calculation becomes more complex because the lower portion is wider than the shaft. In that case, use the manufacturer’s form volume if available or calculate the pier and base separately.

Concrete Footer Calculator

Some people call footings “footers.” A concrete footer calculator works the same way as a footing calculator.

You need:

• Footer length
• Footer width
• Footer depth
• Number of footers
• Waste percentage

Formula:

Length × width × depth ÷ 27 = cubic yards

A footer concrete calculator is especially helpful for long continuous foundation footers where small measurement errors can create a big difference in concrete quantity.

Concrete Foundation Calculator

A concrete foundation calculator may include more than footings. Depending on the project, it may calculate:

• Footings
• Foundation walls
• Slabs
• Piers
• Columns
• Stem walls
• Concrete bags
• Total cubic yards

Calculator.net covers concrete for slabs, square footings, walls, columns, round footings, tubes, curbs, gutters, and stairs, which shows how different concrete shapes require different inputs.

For a complete foundation estimate, calculate each part separately, then add them together.

Footing Size Calculator: What Size Footing Do You Need?

A footing size calculator helps estimate dimensions, but footing size should not be guessed.

Footing size depends on:

• Structure weight
• Soil bearing capacity
• Local building code
• Frost depth
• Footing type
• Foundation design
• Whether the footing supports a wall, post, or column

For small non-structural projects, common footing sizes may be shown in local guides or product instructions. For houses, garages, retaining walls, and load-bearing structures, use engineered plans or local code requirements.

Footing Depth Calculator

Footing depth depends heavily on location and soil conditions.

Exterior footings in cold climates often need to extend below the frost depth to reduce frost heave risk. ICC guidance notes that footings should bear on undisturbed ground and extend below frost depth under non-engineered soil conditions.

Depth may also depend on:

• Local frost line
• Soil type
• Building load
• Drainage
• Ground slope
• Local inspection requirements

A foundation depth calculator can help estimate volume, but it cannot replace local code or engineering requirements.

Foundation Thickness Calculator

Foundation thickness depends on the structure and design. A small shed footing is not the same as a house footing. A deck pier is not the same as a foundation wall.

Thickness may be affected by:

• Load
• Soil bearing capacity
• Reinforcement
• Wall height
• Footing width
• Building code
• Engineering design

Use the calculator to estimate concrete quantity after you know the required thickness. Do not use a calculator alone to choose structural footing thickness.

Concrete Bag Calculator for Footings

If you are using bagged concrete instead of ready-mix delivery, you can estimate bags by dividing the total concrete volume by the yield per bag.

Approximate bag yields:

Example:

You need 24 cubic feet of concrete.

Using 80 lb bags:

24 ÷ 0.60 = 40 bags

So, you need about 40 bags of 80 lb concrete.

How Many Bags of Concrete for a 12×12 Footing?

This depends on whether “12×12” means inches or feet. Big difference.

12 in × 12 in × 12 in Footing

Volume:

1 ft × 1 ft × 1 ft = 1 cubic foot

Approximate bags:

12 ft × 12 ft × 12 in Footing

Volume:

12 × 12 × 1 = 144 cubic feet

Cubic yards:

144 ÷ 27 = 5.33 cubic yards

Using 80 lb bags:

144 ÷ 0.60 = 240 bags

For a footing this large, ready-mix delivery usually makes more sense than bags.

Concrete Footing Cost Calculator

A concrete footing cost calculator estimates cost by multiplying concrete volume by price.

Formula:

Cubic yards × price per cubic yard = concrete cost

Example:

You need 2.5 cubic yards and concrete costs $160 per cubic yard.

2.5 × 160 = $400

That is the concrete material cost only.

A real footing cost estimate may also include:

• Excavation
• Forms
• Rebar
• Gravel base
• Delivery fees
• Short-load fees
• Labor
• Pumping
• Inspection
• Waste

Footing Cost Table

Here is a simple material-only estimate.

Prices vary by location, supplier, mix design, delivery distance, and order size.

Concrete Calculator With Footings, Slabs, and Walls

Many projects need more than one concrete calculation.

You may need:

• Concrete footing calculator for footings
• Concrete slab calculator for slabs
• Concrete wall calculator for foundation walls
• Gravel calculator for base material
• Sand and cement calculator for site-mixed concrete
• Concrete bag calculator for small pours

For example, a small foundation may include:

1. Footings
2. Stem walls
3. Slab
4. Gravel base

Calculate each section separately, then add the totals.

1:2:4 Concrete Mix Calculator

A 1:2:4 concrete mix means:

• 1 part cement
• 2 parts sand
• 4 parts gravel or coarse aggregate

This is a traditional nominal mix ratio, but modern structural concrete is often specified by strength, exposure, slump, and mix design rather than a simple ratio.

Use a 1:2:4 concrete mix calculator only for rough small-project estimates. For structural footings, follow the specified concrete strength and local requirements.

Sand and Cement Calculator for Footings

A sand and cement calculator is useful when mixing concrete on-site. However, for most structural footings, ready-mix concrete is usually more consistent.

If you are site-mixing, you need to estimate:

• Cement
• Sand
• Gravel
• Water
• Total volume
• Waste

Be careful with water. Too much water makes concrete easier to place but can reduce strength and durability. Concrete curing also depends on keeping proper moisture and temperature conditions during early hydration.

Gravel Calculator for Footings

Some footings or slabs may need a compacted gravel base for drainage and support. A gravel calculator estimates the base material by area and depth.

Formula:

Length × width × gravel depth = gravel volume

Then convert to cubic yards:

Cubic feet ÷ 27 = cubic yards

Not every footing needs the same base detail. Follow your plans, local code, or engineer’s recommendation.

Common Types of Concrete Footings

Pad Footings

Pad footings support a concentrated load, such as a column or post. They are often square or rectangular.

Strip Footings

Strip footings are continuous footings that support walls. They are common under foundation walls.

Round Footings

Round footings are often used for decks, porches, pergolas, gazebos, and post-supported structures.

Column Footings

Column footings support vertical columns. They may be isolated pads, piers, or engineered footings.

Slab Footings

Some slabs use thickened edges or integrated footings. This is common in monolithic slab designs.

Common Concrete Footing Mistakes

Measuring in Inches but Calculating in Feet

This is the classic mistake. If your footing is 18 inches wide, convert it to 1.5 feet before using the cubic yard formula.

Forgetting to Divide by 27

Concrete in cubic feet must be divided by 27 to convert to cubic yards.

Not Adding Waste

Footing holes are rarely perfect. Add 10% to 15% extra concrete.

Ignoring Frost Depth

Exterior footings may need to go below frost depth depending on location and code.

Forgetting Rebar and Forms

Concrete volume is only one part of the job. Footings may also need reinforcement, forms, chairs, ties, and inspection.

Using Bagged Concrete for Large Pours

Bags are fine for small footings. For larger projects, ready-mix delivery is usually faster and more consistent.

Adding Too Much Water

More water makes concrete easier to work, but too much water can weaken it. Concrete is not soup. Don’t season it like one.

FAQs

How do you calculate concrete footings?

Measure the length, width, and depth of the footing in feet. Multiply them together to get cubic feet, then divide by 27 to get cubic yards.

Formula:

Length × width × depth ÷ 27 = cubic yards

For multiple footings, multiply by the number of footings.

What is the 4 2 1 rule for concrete?

The 4-2-1 rule is a simple concrete mix ratio:

• 4 parts gravel
• 2 parts sand
• 1 part cement

It is similar to the traditional 1:2:4 mix, just written in reverse order. It can be useful for rough small-project mixing, but structural concrete should follow the specified mix design.

How deep should footings be for a concrete slab?

Footing depth depends on local code, frost depth, soil, and the structure being supported. In cold climates, exterior footings often need to extend below frost depth. For slabs with thickened edges, the required footing depth depends on the design and local inspection rules.

How many bags of concrete for a 12×12 footing?

If the footing is 12 inches × 12 inches × 12 inches, it contains 1 cubic foot of concrete. That is about 2 bags of 80 lb concrete, 3 bags of 60 lb concrete, or 4 bags of 40 lb concrete.

If the footing is 12 feet × 12 feet × 12 inches, it needs about 5.33 cubic yards, which is usually a ready-mix job.

What is the 90 minute rule for concrete?

The 90 minute rule traditionally meant ready-mix concrete should be discharged within 90 minutes after batching or mixing. ACI notes that ASTM C94/C94M used to include a 90-minute discharge requirement, but newer versions allow the time limit to be established between purchaser and producer.

What is the enemy of concrete?

Too much water is one of the biggest enemies of concrete because it can reduce strength and durability. Poor curing, freeze-thaw damage, sulfate attack, chloride exposure, bad drainage, and weak subgrade preparation can also damage concrete over time.

What is a concrete footer calculator?

A concrete footer calculator estimates concrete for footers, which is another common word for footings. It uses footer length, width, depth, and quantity to calculate cubic yards or bags.

How much concrete do I need for footings?

Multiply footing length by width by depth, then divide by 27 to get cubic yards. Add 10% to 15% extra for waste and uneven excavation.

Can I use a concrete slab calculator for footings?

A concrete slab calculator can work for square or rectangular footings if it allows length, width, and thickness inputs. For round piers or post footings, use a round concrete footing calculator.

What is the difference between a footing and a foundation?

A footing is the lower support that spreads the load into the soil. A foundation may include footings, walls, piers, slabs, or other structural support elements.

Final Thoughts

A concrete footing calculator helps estimate concrete volume before you pour. The basic formula is simple:

Length × width × depth ÷ 27 = cubic yards

For round footings, use:

3.1416 × radius² × depth ÷ 27 = cubic yards

For the best estimate, measure carefully, convert inches to feet, add all footings together, and include 10% to 15% extra concrete. Use the calculator for quantity, but follow your plans, local code, and inspection requirements for footing size, depth, reinforcement, and structural design.