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October 13, 2026

Concrete Pad Calculator

Concrete Pad Calculator

Calculate how much concrete you need for a patio pad, shed base, hot tub pad, equipment slab, or other flat concrete surface. Estimate cubic yards, cubic meters, ready-mix bags, and material cost.

Enter Your Pad Measurements

Enter the planned concrete slab thickness.
Allowance for spillage and uneven subgrade.
Enter a price in your local currency.
Your Estimate

Concrete Requirements

Concrete volume
—
cubic yards
Ready-mix bags to buy
—
Including allowance
Estimated bag cost
—
Optional estimate
MeasurementResult

How to Calculate Concrete for a Pad

Concrete volume is the pad’s surface area multiplied by its thickness. Measure the finished pad dimensions and use a consistent unit for all measurements before calculating volume.

Rectangular concrete pad formula

Volume = length × width × thickness

For a rectangular pad, multiply the length by the width to get the area, then multiply that area by the slab thickness.

Circular concrete pad formula

Volume = π × radius² × thickness

Divide the diameter by two to find the radius, calculate the circular area, and multiply by the thickness.

How many bags of concrete do you need?

Divide the volume including your waste allowance by the yield of one bag. Round up to the next whole bag. Bag yields differ by product, so use the yield printed on the packaging when available.

Tips for accurate estimates

  • Measure the actual finished length, width, or diameter.
  • Use the planned slab thickness, not the depth of the entire excavation if it includes a gravel base.
  • Include an allowance for spillage and uneven ground.
  • For large pours, compare bagged concrete with ready-mix delivery costs and minimum order requirements.
  • Prepare a suitable, compacted base and follow local requirements for reinforcement, drainage, and slab design.

Frequently Asked Questions

How much concrete do I need for a 10 × 12 foot pad?

At 4 inches thick, a 10 × 12 foot rectangular pad needs about 1.48 cubic yards before waste. With a 10% allowance, order approximately 1.63 cubic yards.

How many 80 lb bags do I need for a concrete pad?

Divide the total concrete volume in cubic feet, including allowance, by the bag’s stated yield. For an approximate 0.60 cubic foot yield, a 10 × 12 foot pad at 4 inches thick with 10% allowance needs about 74 bags.

Should I include a waste allowance?

A 5–10% allowance is a common starting estimate for straightforward pours. Uneven excavation or difficult placement can require more.

Disclaimer: This calculator estimates material quantities and optional bag cost. It does not provide structural engineering, reinforcement, or site-preparation advice.