Concrete Calculator

Estimate the volume of concrete required for slabs, footings, columns, stairs, and more. Customize your units seamlessly.

Length

Width

Thickness

Quantity (multiplier)

Construction basics

What Is a Concrete Calculator?

A concrete calculator estimates how much concrete a project needs from its dimensions. It helps convert practical measurements into cubic yards, cubic feet, cubic meters, and bag counts.

The calculator is useful before ordering ready-mix concrete or buying premixed bags because it turns slab, hole, tube, curb, and stair measurements into a volume estimate.

How to use it

How to Use This Concrete Calculator

Start with the shape that matches the project, then enter each measurement in the units you already have.

1
Choose the project shape
Select slab, hole, circular tube, curb and gutter, or stairs so the calculator uses the right volume formula.
2
Enter the dimensions
Add the length, width, thickness, height, diameter, or stair details that match the project.
3
Check the units
You can mix feet, inches, meters, centimeters, and yards. The calculator converts each measurement before calculating volume.
4
Review cubic yards and bag estimates
Use cubic yards for ready-mix orders and bag counts for smaller premixed concrete projects.

Project types

What This Calculator Can Estimate

Concrete volume changes by shape. A driveway slab, a post hole, and a set of stairs should not use the same inputs.

Slabs and walls: Use this for patios, driveways, walkways, garage floors, shed pads, walls, and square footings.
Holes and columns: Use this for round post holes, piers, columns, and cylindrical footings where diameter and depth are known.
Circular tubes: Use this when concrete fills a ring-shaped space, such as a tube or circular form with an empty center.
Curbs and gutters: Use this for a combined curb section and gutter flag measured across a total linear length.
Stairs: Use this for solid concrete stairs where run, rise, width, number of risers, and optional platform depth are known.

The math

Concrete Volume Formulas

All modes calculate volume first. After that, the result is converted into the units most commonly used for ordering concrete.

Core rectangular concrete formula

V = L \times W \times T

This is the main formula for slabs, patios, sidewalks, square footings, and walls.

Project	Formula	How to read it
Slab, wall, or footing	$V = L \times W \times T$	Length times width times thickness or depth.
Round hole or column	$V = \pi r^2 h$	Use radius, not diameter. Radius equals diameter divided by 2.
Circular tube	$V = \pi (R^2 - r^2)h$	Subtract the inner cylinder from the outer cylinder.
Curb and gutter	$V = (d_c h_c + w_g t_g)L$	Add curb volume and gutter volume, then multiply by total length.
Solid stairs	$V = rw \times rise \times \frac{n(n+1)}{2} + V_{platform}$	The stair prism grows by each riser, with optional platform volume added.

Ordering units

Cubic Yards, Cubic Feet, and Bags

Large concrete deliveries are commonly discussed in cubic yards. Smaller jobs often use premixed bags, so bag yield matters too.

Conversion	Formula
Cubic feet to cubic yards	$\mathrm{yd}^3 = \frac{\mathrm{ft}^3}{27}$
Cubic meters to cubic yards	$\mathrm{yd}^3 = \mathrm{m}^3 \times 1.30795$
Cubic meters to cubic feet	$\mathrm{ft}^3 = \mathrm{m}^3 \times 35.3147$

Premixed bag estimate

\text{Bags needed} = \left\lceil \frac{\text{total ft}^3}{\text{bag yield}} \right\rceil

Always round up because concrete bags are purchased as whole bags.

Bag size	Approximate yield
60 lb bag	About 0.45 cubic feet
80 lb bag	About 0.60 cubic feet

Planning note

Waste Allowance and Real-Site Conditions

The exact geometry estimate is a starting point. Real pours can require more concrete because job sites are rarely mathematically perfect.

For ordering, many users add a practical allowance for uneven ground, form variation, spillage, and over-excavation. The right allowance depends on the project size, site condition, and contractor guidance.

Common Concrete Estimating Mistakes

These are the details most likely to make a concrete order too low or too high.

Mixing units

Do not multiply feet by inches without converting. A 4 inch slab is 0.333 feet, not 4 feet.

Using diameter as radius

Round-hole formulas use radius. If the diameter is 12 inches, the radius is 6 inches.

Ignoring site variation

Uneven subgrade, over-excavation, form movement, and spillage can all increase the real amount needed.

Confusing cubic feet and cubic yards

Ready-mix concrete is commonly ordered by cubic yard, while small projects often start from cubic feet.

Ordering exact math only

For real pours, many projects need a small allowance beyond the calculated volume.

Frequently Asked Questions

It estimates concrete volume from project dimensions and shows the result in cubic yards, cubic feet, cubic meters, and approximate premixed bag counts.

For a rectangular slab, wall, or footing, use volume equals length times width times thickness.

Divide cubic feet by 27 because one cubic yard contains 27 cubic feet.

Divide the total cubic feet by the bag yield and round up. This calculator uses about 0.45 cubic feet for a 60 lb bag and 0.60 cubic feet for an 80 lb bag.

Usually yes. A small allowance can help cover uneven ground, spillage, and measurement variation, especially on larger pours.

Use the result as an estimate. For foundations, load-bearing work, code-required projects, or structural details, confirm the plan with a qualified contractor or engineer.

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