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Concrete Calculator

Estimate a rectangular slab, patio, walkway, or footing. The result compares bagged concrete with ready-mix and provides volume, ordering quantities, reinforcement, labor, and cost scenarios.

22-calculator project library Reviewed 2026-07-25Calculations run privately in your browser

Enter project details

Example values are prefilled
Slab dimensions
ft
ft
in
%
Materials and cost
$
$
$
$
$
Location and tax assumptions

The location factor adjusts labor only. Replace all default prices with actual local quotes before purchasing.

A coarse planning adjustment—not a ZIP-code quote.

%

Enter the tax rate that applies to taxable materials.

All default prices are editable examples. Cost scenarios vary the entered plan; they do not represent bids or guarantees.

How to use this concrete calculator

Calculate concrete volume, cubic yards, premix bags, ready-mix cost, reinforcement, labor, and waste.

Formula

Cubic feet = length × width × thickness ÷ 12. Cubic yards = cubic feet ÷ 27. Add waste before rounding ready-mix or bag quantities.

Worked example

Example: A 12 × 10 ft slab at 4 in thick contains 40 cu ft, or about 1.48 cu yd. A 10% allowance raises the order quantity to about 1.63 cu yd.

Accuracy and limitations

Excavation depth, uneven grade, thickened edges, footings, pump fees, minimum-load charges, and local mix specifications are not fully captured.

Frequently asked questions

How many 80 lb bags make a cubic yard?

An 80 lb bag is commonly modeled at about 0.60 cu ft, so one cubic yard takes roughly 45 bags before waste.

Should ready-mix be rounded up?

Suppliers often sell in quarter-yard increments and may impose minimums. Confirm the truck's ordering rules.

Is 10% waste always needed?

It is a common planning allowance for grade variation and handling, but well-formed work may need less.

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