Skip to content
Deck Estimate Tools

Deck Footing Concrete Calculator

Estimate concrete volume and bag count for your deck footings. Choose circular or square footings, set depth and count, and edit the bag yield to match your product.

Units
Footing shape

Below grade, per your footing design

80lb ~0.6, 60lb ~0.45, 50lb ~0.375 cu ft

Estimate

Bags to buy(incl. 10% waste)26
Volume per footing2.356 cu ft
Total volume14.137 cu ft
Total volume0.524 cu yd
Total volume0.40032 m³
Bags before waste24

Anyone with this link can view the deck measurements included in it.

Intermediate calculation

Volume per footing = π × (diameter ÷ 2)² × depth. Total = per footing × count. Bags = ceil(total × (1 + waste) ÷ bag yield).

Follow your product packaging

Use the yield printed on the concrete product packaging. Bag weight alone does not guarantee an exact volume across all products. Confirm footing size and depth against local code and frost-depth requirements.

Planning the whole deck? The Project Summary combines boards, joists, fasteners, footing concrete, and railing into one bill of materials you can export as CSV or PDF.

How to use this calculator

  1. Enter the number of footings and pick circular or square.
  2. Enter the diameter, or the width and length for square footings.
  3. Enter the depth of concrete per footing.
  4. Set the bag yield to match your product and choose a waste factor.

Formula with a worked example

circular: volumePerFooting = pi × (diameter/2)² × depth
square: volumePerFooting = width × length × depth
totalCubicFeet = volumePerFooting × footingCount
bags = ceil(totalCubicFeet × (1 + waste) / bagYield)

For six 12 in round footings, 36 in deep, 0.6 cu ft bags, 10% waste:

perFooting = pi × (0.5)² × 3 = 2.356 cu ft
total = 2.356 × 6 = 14.14 cu ft (0.524 cu yd)
bags = ceil(14.14 × 1.10 / 0.6) = 26

Common bag yields

  • 80 lb bag: about 0.60 cubic feet.
  • 60 lb bag: about 0.45 cubic feet.
  • 50 lb bag: about 0.375 cubic feet.

These are editable estimates. The exact yield is printed on your product packaging.

Waste-factor guidance

Concrete is lost to spillage, over-excavated holes, and mixing. A 10% allowance is common; use 15% for irregular or hand-dug holes. See the waste factor guide.

Common mistakes

  • Entering diameter where radius is expected. Enter the full diameter.
  • Mixing inches and feet. Keep every dimension in the selected unit.
  • Using a generic bag yield instead of the printed value.
  • Forgetting that over-dug holes need more concrete.

Limitations & safety notice

Footing design is set by code

This tool estimates concrete volume and bag count for the dimensions you enter. It does not determine required footing size, depth, frost protection, or bearing capacity. Confirm footing design with your local building department and follow the concrete product instructions.

Related deck calculators

Deck Board CalculatorBoards, rows, and linear feet from deck size, board width, gap, and waste.Deck Joist CalculatorJoist count and linear length from spacing and span (quantity only).Deck Fastener CalculatorScrews or hidden clips from board rows and joist count, with boxes.Deck Railing CalculatorPosts, balusters, and rail length across multiple straight runs.Deck Stair CalculatorRisers, treads, stringers, and IRC R311.7 riser/tread/width checks.

Frequently asked questions

How much concrete do I need for deck footings?

Find the volume of one footing, multiply by the number of footings, add a waste factor, then divide by the yield of your concrete bag and round up. The tool shows cubic feet, cubic yards, and bag counts.

How many bags of concrete per footing?

It depends on footing size and bag yield. An 80 lb bag yields roughly 0.6 cubic feet, a 60 lb bag about 0.45, and a 50 lb bag about 0.375. Always use the yield on your bag.

What is the formula for a round footing?

Volume equals pi times the radius squared times the depth. The radius is half the diameter, and all dimensions are converted to feet before multiplying.

Should footings be circular or square?

Both are common. Round forms suit tube-formed piers; square footings suit formed pads. Choose the shape that matches your design and enter the matching dimensions.

Does this tell me how deep footings must be?

No. Footing size, depth, and frost requirements are set by local code and site conditions. This tool only estimates concrete volume for the dimensions you enter.

Why round the bag count up?

You cannot buy a partial bag, and mixing loses a little material. Rounding up after the waste factor helps ensure you can finish the pour.

Methodology & review

This calculator uses the transparent formulas shown above. It estimates material quantities only and does not evaluate structural safety or local code compliance. See our methodology for assumptions and rounding rules. Last reviewed: August 14, 2026.