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Formula For Figuring Concrete Calculator

Calculate concrete in cubic yards, bags, and cubic feet from length, width, and thickness—instantly and free.

  • Free
  • No sign-up
  • Instant results

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How to use it

  1. Enter the length of the area in feet.
  2. Enter the width of the area in feet.
  3. Enter the thickness of the concrete in inches.
  4. Press Calculate to see cubic yards, bags, and cubic feet.

This concrete calculator tells you exactly how much material you need before you mix a single bag. Enter the length, width, and thickness of your pour, and it instantly returns the volume in cubic yards, the number of 80-lb bags, and the total cubic feet. That makes it easy to plan your order, compare bag counts, and avoid paying for more concrete than you actually use. Each standard 80-lb bag yields about 0.6 cubic feet, so the bag count is based on that constant. The cubic yard number matters for ready-mix deliveries, while the bag count helps if you're mixing on site. Read the results this way: cubic yards for ordering from a plant, bags for a DIY job, and cubic feet to double-check your volume. Use the number you need, then round up when you're ready to buy.

Pro tips

  • Add 10% extra for waste, spillage, or uneven subgrades—it's cheaper than running out mid-pour.
  • Round your bag count up to the next full bag; a partial bag isn't realistic on a jobsite.
  • If you're ordering ready-mix, round up to the nearest half cubic yard to keep the truck from coming up short.
  • Don't mix units—always enter length and width in feet and thickness in inches, or your results will be wrong.

Real-life examples

  • Set a 10x10 patio slab at 4 inches thick and know exactly how many bags to buy.
  • Plan a concrete footing for a shed or deck without over-ordering ready-mix.
  • Compare bagged concrete vs. delivery for a small sidewalk or driveway repair.

Case study

Jake needed to pour a 12x12 pad at 4 inches thick. He used the calculator, saw it was 1.78 cubic yards, and ordered 81 bags. With 10% waste, he bought 89, finished the job with two bags to spare, and never ran to the store mid-pour.

Frequently asked questions

How many 80-lb bags of concrete are in a cubic yard?
One cubic yard equals 27 cubic feet. Since each 80-lb bag yields 0.6 cubic feet, you need 45 bags per cubic yard.
How many bags of concrete do I need for a 10x10 slab?
For a 10x10 slab at 4 inches thick, you need about 33.3 cubic feet. That's roughly 56 bags of 80-lb mix, so round up to 56 or buy 10% extra for safety.
What does the cubic yard number mean?
Cubic yards is the standard unit ready-mix concrete is sold in. One cubic yard is 27 cubic feet, so the calculator divides your total cubic feet by 27.
Should I round my bag count up or down?
Always round up. If the calculator says 56.2 bags, buy 57. It's also smart to add 10% for waste, so plan for about 62 bags in that case.
Can I use this calculator for a round concrete tube?
This calculator is for square or rectangular slabs. For round posts or tubes, use a cylinder-specific calculator that asks for diameter and height instead.