Concrete Volume Calculator

Updated Jul 14, 2026 By Jehan Wadia

Introduction

This concrete volume calculator helps you figure out how much concrete you need for your project. It works for slabs, walls, footings, columns, tubes, curbs, and stairs. Just type in your measurements, and the tool does the math for you. It gives you the total volume in cubic feet, cubic yards, and cubic meters. It also tells you how many pre-mix bags to buy and what they will cost.

Ordering too little concrete means extra trips to the store or a short load from the ready-mix plant. Ordering too much wastes money. This calculator adds a waste allowance so you get the right amount the first time. You can set the waste percentage yourself, but 10% is a good starting point for most pours.

Pick the shape that matches your pour, enter your length, width, thickness, or diameter, and hit Calculate. The results update right away with a full breakdown, step-by-step math, bag counts for 40 lb, 60 lb, and 80 lb bags, and a cost estimate you can adjust with your own prices.

How to Use Our Concrete Volume Calculator

Enter the shape and size of your concrete pour, and this calculator gives you the total volume, weight, number of pre-mix bags, and estimated cost.

Pick your shape. Click the tab at the top that matches your project: Slab / Wall / Square Footing, Column / Round Footing / Hole, Circular Slab or Tube, Curb & Gutter Barrier, or Stairs.

Slab / Wall / Square Footing

Length — Type the long side of your slab or wall. Choose your unit (inches, feet, yards, centimeters, or meters) from the dropdown.

Width — Type the short side of your slab or wall. Pick the unit that matches your measurement.

Thickness / Height — Type how thick the slab is or how tall the wall is. For a typical slab, this is often 4 inches.

Quantity — Enter how many identical slabs, walls, or footings you are pouring.

Column / Round Footing / Hole

Diameter — Type the distance across the round column or hole. Pick your unit from the dropdown.

Depth / Height — Type how deep the hole is or how tall the column is.

Quantity — Enter the number of identical columns or holes you need to fill.

Circular Slab or Tube

Outer Diameter — Type the full distance across the outside of the tube or circular slab.

Inner Diameter — Type the distance across the hollow center. This must be smaller than the outer diameter. Set it to 0 for a solid circular slab.

Length / Height — Type how long or tall the tube or circular slab is.

Quantity — Enter how many identical tubes or circular slabs you are pouring.

Curb & Gutter Barrier

Curb Depth — Type the thickness of the vertical curb face (front to back).

Gutter Width — Type how wide the flat gutter part extends out from the curb.

Curb Height — Type how tall the vertical curb section is.

Flag Thickness — Type the thickness of the flat gutter base.

Length — Type the total run of the curb and gutter along the ground.

Quantity — Enter how many identical curb sections you are pouring.

Stairs

Run — Type the depth of each step from front to back. A common run is 11 inches.

Rise — Type the height of each step. A common rise is 7 inches.

Width — Type how wide the staircase is from side to side.

Platform Depth — Type the depth of the flat landing at the top of the stairs.

Number of Risers — Enter the total count of steps in the staircase. Use our stair stringer calculator if you need help determining riser count and layout before your pour.

Quantity — Enter how many identical staircases you are pouring.

Shared Settings and Results

Waste Allowance (%) — This adds extra concrete to cover spills, uneven ground, and form leaks. The default is 10%, which works well for most pours.

Bag Prices — After you calculate, you can change the price per bag for 40 lb, 60 lb, and 80 lb pre-mix bags. The cost estimate updates right away. You can also use our Quikrete calculator for product-specific bag estimates.

Press the Calculate button to see your results. The calculator shows volume in cubic feet, cubic yards, and cubic meters. It also shows estimated weight, the number of pre-mix bags needed, cost for each bag size, a step-by-step math breakdown, and a bar chart comparing bag counts.

Press the Clear button to reset all fields back to their default values.

How to Calculate Concrete Volume

When you pour concrete for a project, you need to know exactly how much to order. Too little means you run out mid-pour. Too much means you waste money. This concrete volume calculator helps you figure out the right amount of concrete for your job in cubic yards, cubic feet, and cubic meters.

What This Calculator Does

This tool calculates the volume of concrete you need for five common shapes: slabs, columns, hollow tubes, curb and gutter barriers, and stairs. You enter your measurements, pick your units, and the calculator does the math for you. It also tells you how many pre-mix bags to buy if you are not ordering a ready-mix truck.

Why Waste Allowance Matters

Concrete pours rarely go perfectly. Some concrete sticks to the mixer. The ground may be uneven. Forms can bulge slightly. That is why you should always order more than the exact volume. A 10% waste allowance is standard for most jobs. For rough ground or complex forms, you may want to add even more. If you are pouring into an excavated area, the actual hole dimensions can vary from the planned ones, making waste allowance even more important.

Choosing Between Bags and Ready-Mix

For small projects like a single fence post or a small pad, pre-mix bags from the hardware store work fine. They come in 40 lb, 60 lb, and 80 lb sizes. For anything over about 1 cubic yard, ordering a ready-mix concrete truck is usually cheaper and much faster. One cubic yard equals 27 cubic feet, which would take about 45 bags of 80 lb mix.

Concrete Weight

Cured concrete is heavy. It weighs about 150 pounds per cubic foot, or roughly 2,400 kilograms per cubic meter. Knowing the total weight helps you plan for delivery, make sure your subgrade can handle the load, and figure out how many workers you need on pour day. If you also need to calculate weight for aggregate or other materials being delivered to your site, plan your subgrade and access route accordingly.

Tips for an Accurate Estimate

Measure twice before you calculate. Use the same units for each dimension, or let the calculator convert them for you. If you need help converting between metric and imperial, our meters to feet calculator can help. If your slab sits on uneven ground, measure the thickness at several points and use the average. For round columns or sonotube holes, measure the diameter across the widest point. Always round up when buying bags — you cannot pour half a bag back into the box. Before pouring, make sure you know the square footage of your form so you can double-check your dimensions, and plan your rebar layout to reinforce the pour properly.

Formulas used

Slab / Wall / Square Footing Volume

V = L \times W \times T \times Q

Column / Round Footing Volume

V = \pi \times \left(\frac{D}{2}\right)^2 \times H \times Q

Hollow Tube / Circular Slab Volume

V = \pi \times \left(\left(\frac{D_o}{2}\right)^2 - \left(\frac{D_i}{2}\right)^2\right) \times L \times Q

Curb & Gutter Volume

V = \left(D_{curb} \times H_{curb} + W_{gutter} \times T_{flag}\right) \times L \times Q

Stairs Volume

V = \left(W \times Rise \times Run \times \frac{n(n+1)}{2} + P \times W \times Rise \times n\right) \times Q

Order Volume with Waste Allowance

V_{order} = V \times \left(1 + \frac{\text{waste\%}}{100}\right)

Estimated Weight

W = V_{order} \times 150 \; \text{lb/ft}^3

Frequently asked questions

How many bags of concrete do I need for a 10x10 slab?

A 10×10 foot slab that is 4 inches thick needs about 1.23 cubic yards of concrete. With 10% waste, that comes to about 1.35 cubic yards or 36.67 cubic feet. You would need roughly 123 bags of 40 lb mix, 82 bags of 60 lb mix, or 62 bags of 80 lb mix. For a pour this size, ordering a ready-mix truck is usually cheaper and faster than buying bags.

What does the waste allowance do?

The waste allowance adds extra concrete to your order to cover spills, uneven ground, and forms that bulge slightly. The default is 10%, which works for most jobs. If your ground is very rough or your forms are complex, raise it to 15% or more. You can set it to 0% if you want only the exact calculated volume.

How do I convert cubic feet to cubic yards?

Divide cubic feet by 27. There are 27 cubic feet in one cubic yard. For example, 54 cubic feet ÷ 27 = 2 cubic yards. This calculator does the conversion for you automatically.

What is the difference between a 40 lb, 60 lb, and 80 lb bag of concrete?

The number refers to how much the bag weighs. A heavier bag yields more mixed concrete. A 40 lb bag makes about 0.30 cubic feet, a 60 lb bag makes about 0.45 cubic feet, and an 80 lb bag makes about 0.60 cubic feet. Heavier bags cost more per bag but less per cubic foot, so they save money on bigger jobs.

How thick should a concrete slab be?

Most residential slabs like patios, sidewalks, and shed floors are 4 inches thick. Driveways should be at least 4 to 6 inches. Garage floors and areas with heavy loads should be 6 inches or more. Thicker slabs use more concrete but are stronger and last longer.

Can I mix different units like inches and feet in the same calculation?

Yes. Each dimension has its own unit dropdown. You can set length in feet, width in feet, and thickness in inches, for example. The calculator converts everything to feet internally before doing the math.

How much does concrete weigh?

Cured concrete weighs about 150 pounds per cubic foot, or roughly 2,400 kilograms per cubic meter. One cubic yard of concrete weighs about 4,050 pounds (1,837 kg). The calculator shows the estimated weight based on your order volume.

When should I use bags instead of ordering a ready-mix truck?

Use bags for small jobs under 1 cubic yard, like a few fence posts, a small pad, or patching work. For anything over 1 cubic yard, a ready-mix truck is usually cheaper and much faster. One cubic yard takes about 45 bags of 80 lb mix, which is a lot of hand mixing.

What is the inner diameter for on the tube calculator?

The inner diameter is the size of the hollow center of a tube or pipe. The calculator subtracts the inner cylinder from the outer cylinder to find the volume of concrete in the walls. If you are pouring a solid circular slab with no hole, set the inner diameter to 0.

How accurate is this calculator?

The math is precise based on the numbers you enter. The accuracy of your result depends on how well you measure. Ground may be uneven, forms can flex, and real dimensions may differ from plans. That is why the waste allowance exists. Measure carefully at several points and use average values for the best estimate.

How do I figure out how many risers my stairs need?

Divide the total height you need to climb by the rise of each step. For example, if you need to go up 35 inches and each riser is 7 inches tall, you need 5 risers. Enter that number in the Number of Risers field on the Stairs tab.

What are curb depth and flag thickness?

Curb depth is how thick the vertical curb face is from front to back. Flag thickness is how thick the flat gutter base is. Together they form the L-shaped cross section of a curb and gutter barrier. The diagram on the Curb tab shows exactly which part each measurement refers to.

Can I change the bag prices?

Yes. After you calculate, you will see price fields under the Estimated Bag Cost section. Type in the actual price you pay at your local store. The total cost updates right away. Prices vary by location, so always check current retail pricing before you buy.

How do I calculate concrete for a round column or sonotube?

Click the Column / Round Footing / Hole tab. Enter the diameter of the tube or hole and the depth or height. Set the quantity to the number of columns you are filling. The calculator uses the formula for a cylinder: π × (diameter ÷ 2)² × height.

Why does the calculator show more concrete than my exact volume?

The order volume includes the waste allowance. By default it adds 10% to the exact calculated volume. This extra concrete covers spillage, uneven subgrade, and minor form bulges. You can lower or raise the waste percentage in the Waste Allowance field.

What if my slab is not a perfect rectangle?

Break the area into smaller rectangles or other shapes. Calculate each section separately using the matching tab, then add the volumes together. For L-shaped or T-shaped slabs, split them into two or three rectangles and sum the results.

Does the quantity field multiply everything?

Yes. If you enter 4 in the quantity field, the calculator multiplies the volume of one unit by 4. This is useful when you have several identical columns, slabs, or stairs to pour at once.

How many cubic yards are in a concrete truck?

A standard ready-mix truck holds about 10 cubic yards. Most companies will deliver partial loads, but they often charge a short-load fee for orders under 5 or 6 yards. Check with your local supplier for their minimum order and pricing.