How to use it
- Enter the slab length in feet
- Enter the slab width in feet
- Enter the thickness in inches
- Click Calculate to see cubic yards, cubic feet, and 80-lb bag count
This calculator turns your slab dimensions into the exact amount of concrete mix you need — no guesswork. Just type in length, width, and thickness, and it instantly returns cubic feet, cubic yards, and the number of 80-lb bags (each bag yields 0.6 cubic feet). Why does this matter? Because ordering too little means a trip to the store mid-pour; ordering too much wastes money and leaves you with heavy leftovers. The result shows both volume and bag count, so you know exactly what to buy. For example, a 10 ft x 10 ft slab at 4 inches thick is 33.3 cubic feet, about 1.23 cubic yards, and needs 56 bags. Use the numbers to compare with ready-mix delivery for larger jobs. Bookmark this tool for your next patio, walkway, or footing — it's free and ready whenever you are.
Pro tips
- Add 10% waste for spillage, uneven subgrade, or slight over-dig — order 1.1x the bag count
- Round bag count up to the nearest whole bag, never down, to avoid a mid-pour shortfall
- For small jobs, buy bags from the same batch; for large slabs, order ready-mix instead of 100+ bags
- Double-check thickness in inches — mixing feet and inches is the #1 cause of wrong concrete orders
Real-life examples
- Pouring a 12x12 ft patio slab at 4 in thick and need to know how many bags to haul
- Building a 2 ft x 2 ft footing for a deck post and want the exact bag count without overbuying
- Planning a 20 ft x 30 ft driveway and comparing bag cost vs. ready-mix delivery
Case study
Mark planned a 10x12 ft shed slab at 5 in thick. He used the calculator and saw he needed 55.6 cubic feet — about 2.06 cubic yards and 93 bags. He added 10% waste, ordered 103 bags, and finished the pour without a second trip. No leftover piles, no mid-pour panic.