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Construction

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Construction

Concrete Patio Calculator.

Estimates the volume of concrete needed for a rectangular patio slab and the number of 80 lb bags required.

Results update live as you type.
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Your inputs

How it works

  1. 1

    Measure the length and width of the patio in feet.

  2. 2

    Decide on the slab thickness in inches (typically 4 inches).

  3. 3

    Multiply length × width × (thickness ÷ 12) to get cubic feet.

  4. 4

    Divide by 0.6 (cubic feet per 80 lb bag) and round up for bags.

length * width * (thickness / 12)

Frequently asked questions

How many cubic feet does an 80 lb bag of concrete cover?

An 80 lb bag of concrete mix yields about 0.6 cubic feet when mixed.

What thickness should I use for a patio?

A standard patio slab is 4 inches thick. For heavier loads, consider 5-6 inches.

Should I order extra concrete?

It's wise to add 5-10% extra to account for waste, spillage, or uneven subgrade.

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Results

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Concrete Volume

40cu ft

80 lb Bags Needed67bags
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Estimate for general guidance only — verify important decisions with an appropriate professional.

How it works

Estimates the volume of concrete needed for a rectangular patio slab and the number of 80 lb bags required.

  1. Measure the length and width of the patio in feet.
  2. Decide on the slab thickness in inches (typically 4 inches).
  3. Multiply length × width × (thickness ÷ 12) to get cubic feet.
  4. Divide by 0.6 (cubic feet per 80 lb bag) and round up for bags.

Formulas

The math behind this calculator, written out so you can verify the result.

Volume of a rectangular slab

V = L × W × T

Multiply length, width, and thickness (converted to feet) to get cubic feet.

Example:

Input: L=12 ft, W=10 ft, T=4 in

Calculation: 12 × 10 × (4/12) = 40 cu ft

Result: 40 cubic feet

Bags of concrete

Bags = ceil(V / 0.6)

Each 80 lb bag yields about 0.6 cubic feet, so divide volume by 0.6 and round up.

Example:

Input: V=40 cu ft

Calculation: 40 / 0.6 = 66.67 → 67 bags

Result: 67 bags

Real-world use cases

Where this calculation shows up in everyday life.

Planning a new patio

Estimate concrete volume and bag count before purchasing materials.

Example: A 12×10 ft patio at 4 inches thick needs 40 cu ft, about 67 bags.

Comparing ready-mix vs bagged

Use the volume to get quotes from ready-mix suppliers or calculate bag costs.

Example: For 150 cu ft, ready-mix might be more economical than 250 bags.

Budgeting for a DIY project

Know exactly how many bags to buy and the total cost.

Example: At $5 per bag, 67 bags cost about $335.

Tips and common mistakes

Tips

  • Add 5-10% extra volume for waste and spillage.
  • Check local building codes for minimum thickness requirements.
  • Prepare a level, compacted subgrade to avoid uneven settling.
  • Use a concrete calculator for irregular shapes by breaking them into rectangles.

Common Mistakes to Avoid

  • Forgetting to convert thickness from inches to feet.
  • Not rounding up bag count, leading to a shortage.
  • Ignoring waste and ordering exactly the calculated amount.

Assumptions and limitations

  • Use the stated inputs and units.
  • Results are estimates for planning and education.
  • Check measurements and source data before making an important decision.