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Concrete Calculator

Estimate slab volume, waste allowance, and material cost.

Your numbers

Make it your own
Updates as you type
Concrete to order
2.716yd³

Calculated from your inputs · rounded for display

Net volume2.4691yd³
Waste allowance10%
Estimated material cost$407.41

Rectangular slab only. Verify thickness, base preparation, structural requirements, and supplier minimums separately.

Your calculation, step by step

No black boxes
  1. 20 ft × 10 ft × (4 in ÷ 12) ÷ 27 = 2.469136 yd³.
  2. Order volume = 2.469136 × (1 + 10/100) = 2.716049.

What if things were different?

Save up to three scenarios, then change your inputs to compare the possibilities.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

US yd³ = length (ft) × width (ft) × depth (in) / 12 / 27

A rectangular slab volume is length times width times thickness. US inputs use feet for the sides and inches for thickness; metric inputs use meters and centimeters. A waste allowance increases the net volume. This tool estimates quantity only and does not determine safe structural thickness.

A worked example

20 ft × 10 ft × (4 in ÷ 12) ÷ 27 = 2.469 yd³. A 10% allowance gives about 2.716 yd³.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

Does this cover footings or cylinders?

No. The first release models a rectangular slab.

Is the waste allowance guaranteed?

No. Uneven subgrade, spillage, and supplier requirements can change the quantity needed.

Sources & methodology

This calculator uses the mathematical identity and assumptions stated above. No current rates, prices, or external data are loaded. Conversion tools use international unit definitions.

Formula review: October 24, 2026. Read our methodology.