How to use it
- Enter the slab length in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Click calculate to see cubic yards, cubic feet, and bag count.
Use this cement calculator to get the exact amount of concrete mix for your next slab, footing, or patio. Enter the length and width in feet, plus the thickness in inches, and you'll instantly see the volume in cubic feet and cubic yards, along with the number of standard 80-lb bags needed. No guesswork, no over-ordering, no running short mid-pour.
Why it matters: concrete is heavy and expensive to return or reorder. Knowing your numbers upfront saves time, money, and a lot of trips to the home store. The calculator uses the standard yield of 0.6 cubic feet per 80-lb bag, so your estimate matches what the bag label says.
Reading the results is simple: cubic yards is what ready-mix trucks use; bags are what you'd carry home. If your project is small, use the bag count. If it's large, use the cubic yards to order from a ready-mix supplier.
Pro tips
- Add 10% waste allowance to cover spills, uneven subgrade, or slight miscalculations.
- Round up to the next whole bag — partial bags aren't practical for mixing.
- Order all your bags in one trip to avoid color or strength variations between batches.
- Double-check thickness at several points; a thin spot can throw off your whole estimate.
Real-life examples
- Pouring a 12x12 patio slab and need to know how many bags to buy.
- Building a small shed foundation and comparing bag vs ready-mix cost.
- Patching a driveway section and estimating the exact concrete volume.
Case study
Before, Mark guessed and ordered 10 extra bags for his 8x10 slab at 4 inches thick. After using the calculator, he learned he needed exactly 44 bags — bought the right amount, saved $60, and finished in a day.