Decks Concrete Calculator

Calculate your concrete volume in cubic yards, cubic feet, and required 80‑lb bags instantly and free.

  • Free
  • No sign-up
  • Instant results

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How to use it

  1. Enter length in feet.
  2. Enter width in feet.
  3. Enter thickness in inches.
  4. Read cubic yards, cubic feet, and bag count.

What it does – You input the deck’s length, width, and thickness. The tool converts thickness to feet, multiplies the three dimensions to get total cubic feet, then shows the equivalent in cubic yards (1 yd³ = 27 ft³) and estimates how many 80‑lb bags you’ll need (each bag ≈ 0.6 ft³).
Why it matters – Ordering too little concrete delays the project; ordering too much wastes money and space. Seeing all three units lets you compare supplier quotes and plan deliveries.
How to read the resultsCubic feet is the raw volume of your deck. Cubic yards is the standard ordering unit for most mixers. Bags tells you the number of 80‑lb bags to purchase; round up to the next whole bag.

Pro tips

  • Add 5‑10% extra for spillage and uneven subgrade.
  • Always round bag count up to the next whole bag.
  • Order bags in multiples of 5 to get bulk discounts.
  • Double‑check thickness conversion; 1 in = 0.0833 ft.

Real-life examples

  • A homeowner estimating concrete for a 12 ft × 16 ft patio.
  • A contractor pricing a 20 ft × 30 ft garage floor.
  • A landscaper planning a 10 ft × 10 ft stepping stone area.

Case study

John needed a 12 × 20 ft deck 4 in thick. Using the calculator he saw 0.89 yd³, which translated to 53 bags. He ordered 55 bags, avoiding a costly second delivery and finishing the project on schedule.

Frequently asked questions

What units does the calculator use?
Enter length and width in feet, thickness in inches; results are shown in cubic feet, cubic yards, and 80‑lb bags.
Why does the bag count differ from the cubic‑yard total?
Bags are measured by volume (0.6 ft³ each) while yards are a larger unit (27 ft³), so the numbers won’t match directly.
Should I add extra concrete for waste?
Yes, add 5‑10 % to the cubic‑foot result before converting to bags to cover spillage and uneven subgrade.
Can I use the calculator for slabs thicker than 12 in?
Yes, just enter the thickness in inches; the tool handles any reasonable value.
Do I need to sign up to get the results?
No, the calculator provides instant results for free with no registration.