How to use it
- Enter the length of your slab or footing in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Click Calculate to see cubic yards, 80-lb bags, and cubic feet.
This Cemex Concrete Calculator tells you exactly how much concrete you need before you order or mix. Just enter the length, width, and thickness of your pour. It instantly shows three numbers: cubic yards, 80-lb bags, and cubic feet.
Cubic yards is what ready-mix companies quote. Bags matter if you're mixing on site — each standard 80-lb bag yields about 0.6 cubic feet. Cubic feet helps you compare with bag labels or small mixers.
Reading the results is simple. If you see 1.5 cubic yards, that's how much truck to order. If you see 67 bags, that's how many 80-lb bags to buy. For most DIY jobs, bags are easier to control. For big slabs, ready-mix wins.
No formulas, no guesswork. The calculator does the converting so you order the right amount the first time.
Pro tips
- Add 10% for waste, spillage, and uneven subgrades — concrete always disappears faster than expected.
- Round bag count up to the nearest whole bag; you can't buy a fraction of a bag.
- Order ready-mix slightly over your yardage (e.g., 0.5 cu yd more) to avoid a short load.
- Don't confuse thickness in inches with feet — enter inches exactly as shown, the calculator handles the conversion.
Real-life examples
- A patio slab 20 ft by 12 ft at 4 in thick — how many 80-lb bags and do you need a truck?
- A footing for a small shed measuring 8 ft by 8 ft at 6 in thick — bags or ready-mix?
- A walkway 30 ft by 3 ft at 3.5 in thick — estimating cost before heading to the store.
Case study
Mark needed a 10x12 ft slab at 4 in thick. He guessed 50 bags. The calculator showed 2.22 cubic yards, which is 100 bags. He bought 110 with waste. The pour came up short by 8 bags — but he had them on hand. No rush trip.