How to use it
- Enter the slab's length in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Click Calculate to see cubic yards, bags, and cubic feet.
This calculator tells you exactly how much concrete to order for your Cemex project. Enter the length, width, and thickness of your slab, and it instantly converts to cubic yards (the unit ready-mix suppliers use), cubic feet, and the number of standard 80-lb bags you'll need. Each 80-lb bag yields about 0.6 cubic feet, so the bag count is always accurate for that mix. Why does this matter? Ordering too little means a cold joint and a weak slab; ordering too much wastes money. The result shows your total volume in all three units, so you can match your supplier's quote or your trailer's capacity. For example, a 10×10 ft slab at 4 inches thick is about 1.23 cubic yards and needs 56 bags (rounding up). Use it before you buy materials, rent a mixer, or schedule a delivery – it takes seconds and removes guesswork.
Pro tips
- Add 10% waste to your bag count to cover spillage, uneven subgrades, or small framing gaps.
- Round your bag count up to the nearest whole bag – never round down, as patchwork is weak.
- For ready-mix, round to the nearest quarter cubic yard and confirm with your supplier – they often have minimums.
- Double-check thickness in inches; a common mistake is entering depth in feet by accident, which throws off volume by 12x.
Real-life examples
- Pouring a 12×16 ft patio slab and needing to know how many bags to haul from the store.
- Estimating concrete for a 2×4 ft footing before setting a mailbox post.
- Planning a 4×8 ft sidewalk section to compare ready-mix delivery vs. bagged concrete.
Case study
Jake needed a 10×10 ft slab for a shed. He guessed 50 bags, but used the calculator first – it showed 1.23 cubic yards and 56 bags. He added 10% waste, ordered 62 bags, and finished with one bag extra. No trips back, no wasted concrete.