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Concrete Calculator

Estimate concrete cubic feet, cubic yards, waste allowance, bag count, and optional ready-mix cost for rectangular slabs and footings.

Enter pour length in feet.

Enter pour width in feet.

Enter slab or footing thickness in inches.

Optional number of identical pours.

Optional extra percentage for overage, spillage, and uneven subgrade.

Choose a common pre-mix bag size for bag estimates.

Optional ready-mix price for a rough cost estimate.

Status: initial

Results

Awaiting calculation

Material estimate

Introduction

The Concrete Calculator estimates concrete volume for rectangular slabs, pads, and footings from length, width, and thickness.

For a rectangular pour, multiply length by width by thickness in feet. Divide cubic feet by 27 to convert to cubic yards, then add waste allowance.

Formula and method guide

Cubic feet

Cubic Feet = Length(ft) x Width(ft) x Thickness(ft)

This estimates the volume of one rectangular pour.

Cubic yards

Cubic Yards = Cubic Feet / 27

Ready-mix concrete is commonly estimated in cubic yards.

Bag estimate

Bags = Cubic Feet with Waste / Bag Yield

Use this only as a planning estimate for bagged concrete.

Variables

Length

The long side of the rectangular slab, pad, or footing.

Width

The short side or cross-section width.

Thickness

The slab or footing depth in inches.

Waste

Extra allowance for subgrade, forms, spillage, and ordering margin.

Bag size

A common pre-mix bag size used for rough bag estimates.

FAQs

What does this Concrete Calculator calculate?
It estimates cubic feet, cubic yards, waste-adjusted cubic yards, bag count, and optional ready-mix cost.
How do you calculate concrete for a slab?
Multiply length by width by thickness in feet, then divide cubic feet by 27 for cubic yards.
How many cubic feet are in a cubic yard?
There are 27 cubic feet in one cubic yard.
Why is thickness entered in inches?
Slab and footing thickness is commonly measured in inches, then converted to feet for volume.
What waste allowance should I use?
Many projects use 5% to 10% as a planning allowance, but actual needs vary.
Does this calculate post holes?
No. This first version estimates rectangular slabs, pads, and footings.
Does this calculate circular columns?
No. Cylinders need a different formula and should use a future cylinder or post-hole calculator.
How are concrete bags estimated?
The calculator divides waste-adjusted cubic feet by approximate bag yield and rounds up.
Are bag yields exact?
No. Bag yields are approximate and vary by product and mixing.
Can I estimate ready-mix cost?
Yes, enter an optional price per cubic yard for a rough cost estimate.
Does this include delivery fees?
No. Delivery, short-load, pump, labor, reinforcement, and finishing costs are not included.
Can I use this for footings?
Yes for rectangular footings when length, width, and depth are known.
Can I use this for stairs?
No. Concrete stairs need a more specific shape-based calculator.
Should I order exactly the calculated amount?
Usually no. Confirm waste, supplier rounding, and job conditions before ordering.
Is this construction advice?
No. It is a planning calculator and not structural, engineering, or code advice.

References

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