📊 Data sourced from publicly available industry standards. See our methodology page for formulas, sources, and limitations.

If you’ve ever tried to estimate concrete for a patio, slab, or footing, you know the frustration: most online calculators only support 80lb bags and completely ignore cost. That means you’re left guessing how many bags to buy for different brands or sizes, and you still have to multiply bag count by price yourself. Our bagged concrete calculator changes that.

We support 40lb, 60lb, 80lb, and 90lb bags — the most common sizes from QUIKRETE, Sakrete, and other brands. Plus, we add a cost-per-bag field so you see the total project cost instantly. No more manual math, no more surprises at the register.

Real numbers: A standard 4-inch thick, 10x10 ft slab needs about 1.23 cubic yards of concrete. Using 80lb bags (0.6 cu ft each), that’s roughly 56 bags. At $6.50 per bag, your material cost is $364. Our calculator shows you that in seconds — and lets you compare costs with 60lb or 90lb bags.

Concrete Bag Calculator — Operation Manual

1. Input Parameters

• Step 1 — Dimension Entry: Project dimensions (length, width, depth).
  Units: inches or feet (selectable).
  Depth for slabs: use actual thickness.
    • Walkway: 4 in (0.333 ft)
    • Driveway: 6 in

Not all concrete bags are created equal. Here’s a quick reference based on industry standards (per QUIKRETE and Sakrete technical data):

• 40lb bag: Yields ~0.30 cu ft — good for small repairs or stepping stones. At $4.50/bag, a 1 cu ft project costs ~$15.
• 60lb bag: Yields ~0.45 cu ft — ideal for fence posts or small slabs. At $5.50/bag, a 1 cu ft project costs ~$12.22.
• 80lb bag: Yields ~0.60 cu ft — the most common for patios and footings. At $6.50/bag, a 1 cu ft project costs ~$10.83.
• 90lb bag: Yields ~0.68 cu ft — often used for thicker slabs or commercial work. At $7.50/bag, a 1 cu ft project costs ~$11.03.

Using our calculator, you can instantly compare these options. For a 4x4 ft, 4-inch thick slab (0.2 cu yd), you’d need about 9 x 80lb bags ($58.50) vs. 12 x 60lb bags ($66). The 80lb bags save you $7.50 and reduce trips to the store.

Even experienced DIYers make errors. Here are the top three and how our calculator helps:

• Mistake 1: Ignoring depth variations. Many people measure length and width but forget that a 6-inch deep footing needs twice the concrete of a 3-inch deep one. Our calculator asks for depth in inches, so you get a precise volume.
• Mistake 2: Using the wrong bag size. If you assume all bags are 80lb, you might over- or under-order. Our tool lets you toggle sizes instantly.
• Mistake 3: Forgetting the cost. Without a cost field, you might buy bags at $7 each when a store down the street sells them for $5.50. Our cost estimate helps you budget and compare prices.

For a typical 8x10 ft shed slab (4 inches thick), the difference between 60lb and 80lb bags is about 10 bags and $15. Our calculator shows this in one click.