Concrete Calculator

Introduction

Ordering too much or too little concrete for a project wastes money and time. This concrete calculator helps you figure out exactly how much concrete you need before you start pouring. Simply enter your measurements and get the volume, weight, and estimated cost of concrete for your project in seconds.

The calculator handles five common shapes: flat slabs (like driveways, patios, and sidewalks), circular slabs, tubes, curbs and gutters, and stairs. Each shape has its own tab with the right input fields, so you only enter the measurements that matter. You can switch between imperial and metric units for both your inputs and results, making it useful no matter where you are working.

You can also set a custom price per unit volume and adjust the concrete density to match the specific mix you plan to use. The default density is set to 133 lb/ft³, which is a standard value for ready-mix concrete. By getting an accurate estimate up front, you can order the right amount of material, keep your budget on track, and avoid costly delays on the job site.

How to use our Concrete Calculator

Enter the dimensions of your concrete project and the calculator will tell you the volume of concrete needed, the weight of that concrete, and the total material cost. Choose from five shape types: Flat, Circular, Tube, Curb, or Stairs.

Shape Type (Tab Selection): Pick the tab that matches your project. "Flat" is for slabs and rectangular pours. "Circular" is for round slabs like footings. "Tube" is for hollow cylindrical shapes. "Curb" is for curb and gutter work. "Stairs" is for concrete step structures.

Width — For flat slabs and stairs, enter how wide the area is. You can choose feet, inches, yards, centimeters, or meters.

Length — For flat slabs and curbs, enter the length of the area you plan to pour.

Thickness — Enter how thick or deep the concrete pour will be. This field appears for flat, circular, and tube shapes.

Diameter — For circular slabs, enter the full diameter of the round area.

Outer Diameter — For tube shapes, enter the diameter of the outside edge of the tube.

Inner Diameter — For tube shapes, enter the diameter of the hollow center. This must be smaller than the outer diameter.

Curb Depth — For curb projects, enter the depth of the curb face from front to back.

Gutter Width — For curb projects, enter how wide the gutter section is.

Curb Height — For curb projects, enter how tall the raised curb portion is above the gutter.

Flag Thickness — For curb projects, enter the thickness of the flat base layer beneath the curb and gutter.

Run — For stairs, enter the horizontal depth of each step (tread depth).

Rise — For stairs, enter the vertical height of each step.

Platform Depth — For stairs, enter the depth of the top landing platform.

Number of Steps — For stairs, enter how many steps the staircase will have.

Cost — Enter the price of concrete per unit volume. You can set this as cost per cubic foot, cubic yard, or cubic meter.

Density — Enter the density of the concrete mix you plan to use. The default is 133 lb/ft³, which is standard for most ready-mix concrete. You can also enter a value in kg/m³.

Concrete Calculator – Estimate Volume, Weight, and Cost

Concrete is one of the most widely used building materials in the world. It is a mix of cement, water, sand, and gravel that hardens into a strong, solid surface. Whether you are pouring a driveway, building a patio, setting fence posts, or constructing stairs, knowing how much concrete you need before you start is important. Ordering too little means delays, and ordering too much wastes money.

How Concrete Volume Is Calculated

The amount of concrete you need depends on the shape of the area you are filling. For a flat slab like a sidewalk or patio, you multiply the width, length, and thickness together to get the volume. If you need help determining the area of your slab first, our square footage calculator can help. For a circular slab, such as a round pad for a fire pit, the formula uses the diameter and thickness along with pi (π). A tube or hollow column calculation subtracts the inner cylinder from the outer cylinder to find only the concrete portion. Curbs and gutters combine the flag (flat base) and the raised curb section into one total volume. Stairs are calculated step by step, stacking each rise on top of the next and including the top platform.

Concrete Is Sold by Volume

Concrete is typically sold by the cubic yard in the United States or by the cubic meter in countries that use the metric system. One cubic yard equals 27 cubic feet. Ready-mix concrete delivered by a truck is priced per cubic yard, while bagged concrete from a hardware store is sold by weight — usually in 40, 60, or 80 pound bags. Knowing the total volume lets you figure out how many bags you need or how large of a truck order to place.

Why Density Matters

Standard concrete has a density of about 133 to 150 pounds per cubic foot (roughly 2,130 to 2,400 kg/m³), depending on the mix. Lightweight concrete uses special aggregates and weighs less, while heavyweight concrete is used for radiation shielding and weighs more. The density value helps you estimate the total weight of your pour, which is useful for planning structural support and delivery logistics.

Tips for Ordering Concrete

• Add 5–10% extra to your calculated volume to account for spillage, uneven ground, and slight variations in formwork.
• Check the thickness carefully. Even a small change in slab thickness makes a big difference in total volume. Going from 4 inches to 5 inches thick adds 25% more concrete.
• Prepare your forms and base before the concrete arrives. Ready-mix concrete begins to set within about 90 minutes.
• Consider the mix type. Higher-strength mixes (like 4,000 PSI) cost more but are needed for driveways and structural footings. A standard 2,500 PSI mix works fine for most walkways and patios.

Common Concrete Projects and Typical Thicknesses

Related Construction Calculators

Once you have your concrete estimate, you may need to plan other aspects of your project. If your project involves concrete block walls, use our concrete block calculator to estimate the number of blocks needed. For projects that require steel reinforcement, our rebar calculator can help you determine how much rebar to order. If you are building a retaining wall alongside your concrete work, check out the retaining wall calculator. For laying pavers around a concrete patio, try the paver calculator.

Working on other parts of the property? Our gravel calculator helps estimate base material for driveways and walkways, the sand calculator is useful for bedding layers, and the asphalt calculator can help if part of your project uses asphalt instead of concrete. For interior finishing work, tools like our flooring calculator, drywall calculator, tile calculator, and paint calculator can assist with material planning. If you need to join concrete blocks or bricks, our mortar calculator and brick calculator are also helpful resources.

Using a concrete calculator saves you time and money by giving you an accurate estimate before you buy materials or schedule a delivery. Just enter your measurements, choose your shape, and let the calculator do the math for you.

Frequently Asked Questions

How many bags of concrete do I need for my project?

First, use the calculator to find your total volume. Then divide by the yield per bag. An 80-lb bag makes about 0.6 cubic feet of concrete. A 60-lb bag makes about 0.45 cubic feet. So if you need 6 cubic feet, you would need 10 bags of 80-lb concrete (6 ÷ 0.6 = 10). Always round up and buy a couple extra bags.

How do I convert cubic feet to cubic yards?

Divide the number of cubic feet by 27. There are 27 cubic feet in one cubic yard. For example, 81 cubic feet ÷ 27 = 3 cubic yards. This is important because ready-mix concrete trucks sell concrete by the cubic yard.

What is the difference between the Flat and Circular tabs?

The Flat tab is for rectangular shapes like driveways, patios, and sidewalks. It uses width × length × thickness. The Circular tab is for round shapes like round footings or fire pit pads. It uses the diameter and thickness with the formula π × radius² × thickness.

What does the Tube tab calculate?

The Tube tab calculates concrete for hollow cylindrical shapes, like concrete pipe or a ring-shaped footing. You enter the outer diameter, inner diameter, and thickness. The calculator finds the volume of the outer cylinder, subtracts the inner hollow part, and gives you only the concrete portion.

What do the curb inputs mean?

Curb Depth is how deep the curb face is from front to back. Gutter Width is how wide the flat gutter section is. Curb Height is how tall the raised curb is above the gutter. Flag Thickness is the thickness of the flat base layer under the whole curb and gutter. Length is how long the curb runs.

What is the difference between run and rise for stairs?

The run is the horizontal depth of each step — how far it goes from front to back. The rise is the vertical height of each step — how tall each step is. Together they set the size and slope of your staircase.

What is platform depth for stairs?

Platform depth is the depth of the flat landing area at the very top of the staircase. This is the surface you step onto after climbing the last step. It is measured from front to back, just like the run of a step.

Can I change the unit of measurement for each input?

Yes. Every input field has a dropdown menu next to it where you can pick feet, inches, yards, centimeters, or meters. You can mix units too — for example, set width in feet and thickness in inches. The calculator converts everything automatically.

What does the density setting do?

The density setting tells the calculator how heavy the concrete mix is per unit of volume. This is used to calculate the total weight of your pour. The default is 133 lb/ft³, which is standard for regular ready-mix concrete. If you use a lightweight or heavyweight mix, change this number to match your mix.

How do I switch the results between imperial and metric?

Below the Calculate button, in the results section, you will see two buttons labeled Imperial and Metric. Click Imperial to see volume in cubic feet and weight in pounds. Click Metric to see volume in cubic meters and weight in kilograms. The cost stays in dollars either way.

What is a good default cost for concrete?

The calculator defaults to $5.81 per cubic foot. Concrete prices vary a lot based on your location, the mix type, and whether you buy bags or order a ready-mix truck. Check with your local supplier for current prices and update the cost field to get an accurate estimate.

Why is my inner diameter larger than my outer diameter in the Tube tab?

The inner diameter must always be smaller than the outer diameter. If you enter a larger inner diameter, the calculation will not make sense because you would have negative concrete volume. Double-check your measurements and make sure the outer number is the bigger one.

Does this calculator account for waste and spillage?

No. This calculator gives you the exact volume based on your measurements. In real projects, you should add 5% to 10% extra to cover spillage, uneven ground, and small errors in your formwork. Simply multiply your result by 1.05 or 1.10 to add that buffer.

How thick should my concrete slab be?

It depends on the project. Sidewalks and patios are usually 4 inches thick. Driveways for cars need 4 to 5 inches. Driveways for heavy vehicles need 5 to 6 inches. Garage floors are typically 4 to 6 inches. Foundation footings are 8 to 12 inches thick.

What does the Reset button do?

The Reset button sets all the input fields back to their original default values. This includes all dimensions, units, cost, and density. It is useful if you made many changes and want to start fresh with a clean set of inputs.