Concrete Calculator Updated Nov 28, 2026

Use this free concrete calculator to figure out exactly how much concrete you need for a slab, footing, column, set of stairs, or post holes — in cubic yards, cubic meters, and the number of 40-, 60-, or 80-pound bags. The concrete calculator works in US Customary or metric units, handles five project shapes, and shows the cost of ready-mix concrete at your local price per cubic yard.

How to use this concrete calculator

This free concrete calculator works in five steps. First, pick the project shape that matches your pour — Slab, Footing, Column, Stairs, or Post Holes — using the tabs above. Second, choose your units: US Customary (feet and inches) or Metric (meters and centimeters). Third, enter the dimensions; the concrete calculator handles the math instantly as soon as you click Calculate concrete. Fourth, set your waste percentage — the calculator defaults to 10%, which covers spillage, uneven subgrade, and the small over-dig that happens on every job. Fifth, if you want a cost estimate, type your local ready-mix price per cubic yard into the optional price field. The result panel will then show cubic yards, cubic meters, the number of 40-, 60-, and 80-pound bags needed, and an estimated dollar cost for the pour.

You can switch tabs or units at any time without losing your inputs inside a tab. Use the Copy button on the result panel to send the summary to your clipboard — handy for messaging a supplier or pasting into a notes app on the job site.

How to calculate how much concrete you need

Concrete is a volume-based building material — you buy it by the cubic yard (in the US) or cubic meter (almost everywhere else). To figure out how much concrete you need for your project, work out the volume of the space you're filling, then convert that volume into the unit your supplier uses.

There are 27 cubic feet in one cubic yard, which is why we divide by 27 at the end. If your thickness is in inches, divide it by 12 to convert it to feet first. The same formula works for any rectangular slab — patio, driveway, garage floor, walkway, or sidewalk.

How to calculate concrete for a footing

For a strip footing, the length is your total run (in feet) and the width and depth are usually in inches. Convert both to feet, multiply all three, then divide by 27 to get cubic yards. The calculator above does this automatically once you enter the length of your concrete footing along with its width and depth.

How to calculate concrete for a round column

Round footings, sonotube piers, and columns use the volume of a cylinder. Enter the diameter and height of your concrete column to calculate the amount, and the calculator will multiply by the number of columns or footings or columns you have.

How many bags of concrete do I need?

For small jobs — a few post holes, a small patio, or a concrete repair — bagged concrete is easier than ordering ready-mix. Each bag size yields a known volume of mixed concrete. The yields used by this concrete calculator match manufacturer specs from Quikrete's Concrete Mix product line and other major brands:

The calculator above shows the number of bags for all three sizes automatically. A cubic yard of concrete weighs roughly 4,000 pounds (1,800 kg) when cured, so larger jobs are far cheaper and easier as ready-mix from a truck.

Bagged vs ready-mix: when to switch

As a rule of thumb: under 1 cubic yard → use 80-pound bags or fast-setting concrete; 1 to 2 cubic yards → consider either, but bags get heavy and slow; over 2 cubic yards → ready-mix is almost always cheaper, faster, and gives a better pour. Ready-mix trucks usually carry up to 10 cubic yards of concrete and may charge a short-load fee for small orders, so larger jobs are where ready mix really wins on price per cubic yard. For mix-design specifics and delivery best practices, the National Ready Mixed Concrete Association publishes useful industry references.

Standard concrete thickness by project

Use this table as a starting point for the thickness of concrete on common projects, then confirm with local building codes or a contractor:

Tips for getting accurate results from this concrete calculator

The concrete calculator above is only as accurate as the numbers you feed it. These tips help you avoid the most common ordering mistakes that push real-world usage past the calculated volume:

• Always add 5–10% extra. Spillage, uneven subgrade, and over-dig mean you'll use more than the exact calculation. Coming up short mid-pour means another trip — and a cold joint that weakens the slab.
• Add rebar or wire mesh for any slab that holds vehicles or spans more than a few feet. The concrete calculator covers concrete volume only, not reinforcement. The American Concrete Institute publishes the residential code standard (ACI 332) used by most US contractors.
• Compact and level the base. A sloppy or uneven subgrade wastes concrete and weakens the slab — the low spots quietly fill with extra yardage.

• Plan around the cure. Concrete needs to cure (not just dry) — keep it damp for the first few days and don't load it heavily for at least a week.
• Price per cubic yard varies by region. Ready-mix is normally $120–$180 per cubic yard in the US. Per square foot, expect around $4–$8 for a basic 4-inch slab including labor.
• Short-load fees. Most ready-mix companies add a fee for orders under 3–5 cubic yards of concrete — factor this into bag-vs-truck decisions for smaller jobs.

Common projects this concrete calculator covers

This concrete calculator is built around the projects most homeowners and contractors actually run into. For step-by-step DIY pour guides on any of these, the Family Handyman concrete guides are a solid starting point:

• Patio — rectangular slab, typically 4 inches thick.
• Driveway — 4–5 inches for cars, 5–6 inches for heavier vehicles.
• Walkway and sidewalk — long rectangular slab at 4 inches.
• Garage floors — slab with thickened edge footings.
• Shed or storage slab — small rectangular slab, often 4 inches.
• Footings — strip footings under foundation walls; square footings under columns and posts.
• Columns and piers — round footings, sonotube piers, deck piers.
• Steps and stairs — front steps, garden steps, porch stairs.
• Setting fence posts — concrete poured into post holes around each post; fast-setting concrete works well here.
• Curbs and edging — long, narrow strip pours.

Why our concrete calculator is accurate

This concrete calculator uses the same volumetric formulas that ready-mix suppliers and contractors use on the job site. For rectangular pours, that's length × width × thickness; for round columns and footings, it's π × r² × height; for stairs, it's the stacked-volume sum of each tread. The bag yields used in the calculator (0.30, 0.45, and 0.60 cubic feet for 40-, 60-, and 80-pound bags respectively) come directly from manufacturer specifications for standard pre-blended concrete mix. The weight figure — about 150 pounds per cubic foot, or roughly 4,000 pounds per cubic yard — is the industry reference value documented by the Portland Cement Association. The result is a concrete calculator estimate you can trust enough to bring to your supplier, while still leaving the recommended 5–10% waste buffer so you don't come up short during the pour.

Concrete vs mortar vs stucco vs fast-setting concrete

These are different concrete products and not interchangeable — the concrete calculator above is for standard structural concrete only. See the Wikipedia article on concrete for a deeper background on composition and history:

• Concrete — cement, sand, water, and coarse aggregate (gravel). Used for structural slabs, footings, and columns. Calculate by volume.
• Mortar / mortar mix — cement, sand, and water only (no aggregate). Used to bond bricks, blocks, and stone — not for slabs.
• Stucco — cement-based mix for coating exterior walls. Applied in thin layers, sold by the bag, calculated by surface area not volume.
• Fast-setting concrete — pre-blended bagged concrete that sets in 20–40 minutes. Ideal for setting fence posts, mailbox posts, and small concrete repair jobs where you don't want to wait around.

This calculator is for standard concrete. If you're working with mortar, use a mortar coverage chart from the bag; for stucco, work out the wall area in square feet instead.

Related calculators

This concrete calculator provides estimates for planning purposes only. Concrete yield varies by mix, aggregate, and site conditions. Confirm final yardage with your supplier and consult a qualified contractor for structural decisions. © Anchor AI Tools.