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Concrete Calculator

Work out how much concrete a slab, footing, column, or round pour needs, with the volume in cubic yards or cubic meters and how many 40, 60, or 80 lb bags to buy.

Units

Pour shape

Dimensions

Thickness or depth is the small dimension, entered in inches. Everything runs in your browser. Nothing is uploaded.

Quantity and waste

Concrete is easy to run short. A 5 to 10 percent allowance covers spillage, uneven subgrade, and over-excavation.

Concrete needed
1.36 cubic yards
includes 10% waste. Order ready-mix by the cubic yard for large jobs.
1.36
Cubic yards
1.04
Cubic meters
36.7
Cubic feet
Bags of pre-mixed concrete
123
40 lb bags
82
60 lb bags
62
80 lb bags

Bag counts assume typical yields of 0.3, 0.45, and 0.6 cubic feet. Bags suit small pours; large jobs are cheaper by the truck.

How to calculate how much concrete you need

  1. Pick the pour shape

    Choose a slab, footing, rectangular column, or round pour so the tool uses the right volume formula.

  2. Enter the dimensions

    Type the length, width, and thickness, or the diameter and height for a round pour, in feet and inches or meters and centimeters.

  3. Set quantity and waste

    Enter how many identical pours you are making and a waste allowance of about 5 to 10 percent for spillage.

  4. Read the volume and bags

    See the concrete in cubic yards, cubic meters, and cubic feet, plus how many 40, 60, or 80 lb bags it takes.

Why use this tool

Four common pour shapes

Calculate a rectangular slab, a strip footing, a square or rectangular column, or a round column, tube, or post. Each shape uses the correct volume formula.

Bags or ready-mix

See how many 40, 60, and 80 lb bags of pre-mixed concrete a pour takes, alongside the total in cubic yards and cubic meters for ordering ready-mix by the truck.

Quantity and waste built in

Multiply identical footings or piers in one step, then add a waste allowance so you do not run short from spillage, uneven ground, or over-excavation.

Feet or meters

Work in feet and inches or meters and centimeters and switch at any time. Your measurements convert automatically so the pour size never changes.

Cubic yards, meters, and feet

Every result is shown in cubic yards, cubic meters, and cubic feet at once, so it matches however your supplier or bag label quotes volume.

Runs entirely in your browser

Every calculation happens on your device as you type. Nothing is uploaded, stored, or logged.

About this tool

This concrete calculator estimates how much concrete a pour needs and how many bags it takes to fill. Choose a slab, footing, rectangular column, or round pour, enter its dimensions, and the tool works out the volume and rounds up the bag counts for you. A slab, footing, or column is measured as length times width times thickness, and a round pour uses the area of the circle times its height, so each shape uses the formula a builder would use by hand. Thickness and depth are entered in inches or centimeters because they are usually the small dimension, while lengths and heights are in feet or meters.

Enter how many identical pours you are making, such as a row of matching footings or deck piers, and the volume is multiplied for you. A waste allowance of 5 to 10 percent is added on top, which covers spillage, uneven subgrade, over-excavation, and the concrete left in the mixer or wheelbarrow, since running short mid-pour is far more costly than a little extra. Results appear in cubic yards, cubic meters, and cubic feet together, plus the number of 40, 60, and 80 lb bags, using standard bag yields of 0.3, 0.45, and 0.6 cubic feet. For estimating other materials the paint calculator covers wall coverage, and the unit converter handles any odd measurements.

Treat the figures as a close estimate rather than an exact order. Real volume shifts with form spring, subgrade settling, and how full you screed a slab, so bags are best for small pours while large jobs are cheaper and faster delivered by the truck. Every calculation runs in your browser as you type, and nothing you enter is uploaded, stored, or logged.

Frequently asked questions

How does the concrete calculator work?
For a slab, footing, or column it multiplies length by width by thickness. For a round pour it uses pi times the radius squared times the height. The volume is multiplied by the number of pours, a waste allowance is added, and the result is converted to cubic yards, cubic meters, and cubic feet.
How many bags of concrete do I need?
The tool divides the total volume by the yield of each bag and rounds up. A 40 lb bag makes about 0.3 cubic feet, a 60 lb bag about 0.45 cubic feet, and an 80 lb bag about 0.6 cubic feet, so you see all three counts and can pick the size that suits the job.
How much waste should I add?
A 5 to 10 percent allowance is normal and it is the default here. It covers spillage, uneven or over-excavated ground, and concrete left behind in the mixer. Running short partway through a pour is far more expensive than buying one extra bag, so err on the higher side for footings and rough ground.
Can I calculate footings, columns, and round pours too?
Yes. Choose the footing shape for strip footings and wall bases, the column shape for square or rectangular piers, and the round shape for sonotube columns, posts, and tubes where you enter a diameter and height instead of length and width.
Should I buy bags or order ready-mix?
Bags are convenient for small pours like a few post holes or a single small pad. Once a pour runs to roughly a cubic yard or more, ordering ready-mix delivered by the truck is usually cheaper and much faster than mixing dozens of bags by hand.
Is my data uploaded anywhere?
No. Every measurement and result stays on your device. All calculations run in your browser as you type and nothing is sent to a server, stored, or logged.

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