Concrete Volume Calculator

Background.

This concrete calculator turns a few simple measurements — length, width, thickness, or column diameter — into the exact volume of concrete you need to pour a slab, set a column, or cast a footing. It returns the answer in cubic yards (how ready-mix is sold in the United States), cubic feet, and cubic meters, then converts that volume into the number of 60-pound and 80-pound pre-mix bags required if you are buying from a home center instead of ordering a truck. It also estimates the material cost based on the price per cubic yard you enter. The calculator applies a 10% waste factor by default, which you can adjust between 0 and 20 percent depending on how rough your subgrade is and how confident you are in your formwork.

Concrete volume math is unforgiving in two directions. Under-order, and you end up scrambling for a few extra bags while a slab starts to set — leaving a cold joint that becomes a permanent crack. Over-order by too much, and you pay a short-load fee, or you waste a quarter-yard of material that has nowhere to go once the truck arrives. The geometry behind each shape is straightforward. A slab or footing is a rectangular prism: length times width times thickness. A column is a cylinder: pi times the radius squared, times the height. The trick is that no single dimension is usually given in the same unit. Slabs are described in feet, thicknesses in inches, columns in inches of diameter and feet of height, and the final answer is sold in cubic yards. One cubic yard equals 27 cubic feet, and a 4-inch slab is one-third of a foot thick, so a 10-foot by 10-foot patio at 4 inches comes out to 100 × (4/12) = 33.33 cubic feet, which is 1.23 cubic yards before waste — 1.36 yards once you add the standard 10% cushion.

That cushion is not optional in real construction. The Portland Cement Association and the National Ready Mixed Concrete Association both flag that a perfectly screeded subgrade is rare; over-excavation, settled gravel base, spillage out of the chute, and concrete that hardens in the truck on a hot day all eat into your usable volume. The 10% number is what working concrete finishers use in the field, and most ready-mix dispatchers will quietly round your order up anyway. If your subgrade is uneven or you are pouring into deep footing trenches, push the waste factor to 15%.

Bagged concrete is sold by dry weight, not finished volume, so the conversion is the second place beginners get tripped up. An 80-pound bag of Quikrete or Sakrete yields about 0.60 cubic feet of cured concrete; a 60-pound bag yields about 0.45 cubic feet. That means roughly 60 of the 80-pound bags or 80 of the 60-pound bags fill one cubic yard. Anything more than about half a yard — roughly 30 of the 80-pound bags — and you are working too hard for too little concrete: order ready-mix instead. A standard concrete truck holds about 10 cubic yards, but most suppliers will deliver as little as one yard with a short-load fee of $50–$150. Below one yard, bags win on price and convenience. Above that, the truck wins on price, consistency, and your back.

This calculator does not size rebar, mesh, or fiber reinforcement, and it does not specify the mix design. For most homeowner work — patios, walks, shed pads — a 3,000 PSI mix is standard; driveways and footings exposed to freeze-thaw typically call for 4,000 PSI with air entrainment per ACI 318. Whatever mix you order, the volume math here is the same.

What is concrete volume calculator?

A concrete volume calculator computes the cubic volume of fresh concrete needed to fill a defined shape — most commonly a rectangular slab, a cylindrical column, or a strip or pad footing — and converts that volume into the purchase units the supplier uses. In the United States ready-mix is sold by the cubic yard, dry-mix bags are sold by weight (typically 60 lb or 80 lb), and metric suppliers and most international markets work in cubic meters. The calculator also bakes in a waste factor to account for spillage, subgrade variation, and over-excavation, which is standard practice on every commercial pour.

How to use this calculator.

1. 01Choose the shape — slab, column, or footing — that matches what you are pouring.
2. 02Pick the unit (feet or meters) for your length, width, and thickness measurements.
3. 03Enter length and width for a slab or footing. For a column, leave these and enter the column diameter (in inches) and the column height as the thickness field.
4. 04Enter the slab or footing thickness. Remember that 4 inches is 0.333 ft and 6 inches is 0.5 ft.
5. 05Adjust the waste factor. Leave it at 10% for flat slabs on a clean gravel base, push to 15% for uneven subgrade or deep footings, drop to 5% only if your formwork is dialed.
6. 06Enter your local ready-mix price per cubic yard so the cost estimate is realistic for your market.
7. 07Read the primary result — cubic yards — to size your ready-mix order, and use the 60 lb and 80 lb bag counts to compare against bagged concrete from a home center.

The formula.

For slabs and footings the volume is rectangular: V_ft3 = length × width × thickness, with every dimension first converted to feet (1 m = 3.28084 ft, NIST SP 811). For columns the volume is cylindrical: V_ft3 = π × (d/2)² × h, where the diameter d is converted from inches to feet by dividing by 12 and the height h is converted to feet if you entered meters. The waste-adjusted volume is V_total = V_ft3 × (1 + wasteFactorPercent / 100). That total is then divided by 27 to get cubic yards (since 1 yd³ = 27 ft³) and by 35.3147 to get cubic meters. Bag counts use the Portland Cement Association published yields: a 60-pound bag of standard concrete mix yields 0.45 ft³ of cured concrete, and an 80-pound bag yields 0.60 ft³. The calculator divides total cubic feet by these yields and rounds up to the next whole bag, because you cannot buy a fractional bag. Total cost is simply cubic yards × your entered price per cubic yard, which is how ready-mix dispatchers price the load — pumping, short-load fees, fuel surcharges, and weekend premiums are separate line items not included here.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ACI 211.1 — Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete. American Concrete Institute.
2. [2]Portland Cement Association — Design and Control of Concrete Mixtures, 16th Edition (Kosmatka & Wilson). Reference handbook covering mix design, yield, and bag coverage values used in this calculator.
3. [3]ASTM C94 / C94M — Standard Specification for Ready-Mixed Concrete. Defines ordering, batching, and delivery practices for ready-mix in the United States.
4. [4]ASTM C31 / C31M — Standard Practice for Making and Curing Concrete Test Specimens in the Field. Source for 28-day cylinder strength testing referenced in the curing FAQ.
5. [5]NRMCA — Citizen's Guide to Concrete: ordering, delivery, and short-load policy. National Ready Mixed Concrete Association.
6. [6]ACI 318 — Building Code Requirements for Structural Concrete. Source for 4,000 PSI exterior and footing recommendations.
7. [7]NIST Special Publication 811 — Guide for the Use of the International System of Units (SI). Source for the exact 0.3048 m/ft conversion factor.