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Concrete Calculator — Cubic Yards, 60/80 lb Bags & Cost (Slab, Footing, Post)

Estimate cubic yards, 60 lb and 80 lb bags, and a labeled cost check for a slab, footing, or post hole.

Enter a rectangular pour for cubic yards and bags. The examples below use the same formula for a 10×10 slab, a footing, and round post holes.

Measure the rectangular project length in feet.

Measure the rectangular project width in feet.

Enter the planned finished material depth.

Choose the unit used for the entered material depth.

Enter an allowance appropriate to the site and material.

Select the bag size and approximate yield listed in the QUIKRETE Concrete Mix 1101 data sheet.

Estimate boundary

What this result covers

  • This is a quantity estimate, not a mix, reinforcement, formwork, footing, or structural design.
  • Use the result as a purchasing estimate and verify product instructions, site conditions, and local requirements before work begins.

How the calculation works

Formula

length × width × depth × (1 + waste percentage), divided by labeled bag yield

Assumptions used

  • The project is one rectangular area with a uniform depth.
  • Depth is converted to feet before volume is calculated; one cubic yard equals 27 cubic feet.

Worked calculation breakdown

  1. Convert 4 in to feet: 4 ÷ 12 = 0.333 ft.
  2. Find the rectangular volume: 10 ft × 10 ft × 0.333 ft = 33.333 ft³.
  3. Apply 10% waste: 33.333 ft³ × 1.10 = 36.667 ft³.
  4. Convert to cubic yards: 36.667 ft³ ÷ 27 = 1.358 yd³.
  5. Divide by the selected 0.60 ft³ bag yield and round up: 36.667 ÷ 0.60 = 61.11, so buy 62 bags.

The tool keeps user-entered product values separate from the geometry, then rounds the recommended purchasing quantity up where the material is bought as a whole unit.

Worked example

Project inputs
10 ft × 10 ft × 4 in, 10% waste, 80 lb bag
Purchase result
62 bags after rounding up.

Enter these values in the calculator to reproduce the estimate. The purchase result uses the same tested calculation logic as the live tool.

Purchasing checklist

  1. Confirm dimensions and depth.
  2. Match the selected yield to the bag label.
  3. Confirm delivery and mixing limits.

Common mistakes

  • Mixing inches and feet.
  • Using bag weight as bag yield.
  • Rounding down the bag count.

Sources and methodology

These references support the product values, units, or planning boundaries shown on this page. Always confirm the current instructions for the exact material you buy.

  1. QUIKRETE — Concrete Mix Product No. 1101 Data SheetChecked 2026-07-17

    40/50/60/80/90 lb bags yield approximately 0.30/0.375/0.45/0.60/0.675 ft³.

  2. NIST — Handbook 133 (2026), Appendix E: General Tables of Units of MeasurementChecked 2026-07-27

    The tables give 1 square foot as 144 square inches, 1 cubic foot as 1,728 cubic inches, and 1 cubic yard as 27 cubic feet.

Slab, footing, and post-hole examples

Volume is length × width × depth in feet, then ÷ 27 for cubic yards. Bag counts use the QUIKRETE Concrete Mix yields already on the form and round up. The cost column is a labeled hypothetical so you can see the comparison; call the plant for a real price.

ProjectVolume80 lb bags (0.60 ft³)60 lb bags (0.45 ft³)Labeled cost check
10×10 ft slab, 4 in, no waste33.33 ft³ = 1.23 yd³567556 × $6.50 = $364 in bags
Same slab, 10% waste36.67 ft³ = 1.36 yd³62821.5 yd × $160 + $75 short load = $315
40 ft footing, 16 in × 8 in35.56 ft³ = 1.32 yd³6080Price it the same way: yards × plant price
4 post holes, 12 in diameter × 24 in6.28 ft³ = 0.23 yd³1114Hole volume only; the post displaces a little

Related measuring guides: measure a slab, fence post holes, bags versus ready-mix, and round forms.

Questions from search

How many yards of concrete for a 10×10 slab at 4 inches?

10 ft × 10 ft × (4 ÷ 12) ft = 33.33 cubic feet, which is 1.23 cubic yards before waste. With the 10% waste example used in the calculator, the order is 1.36 cubic yards.

How many 80 lb or 60 lb bags is a 10×10×4 inch slab?

Using the labeled yields on this page (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³), the net 33.33 ft³ is 56 bags of 80 lb or 75 bags of 60 lb. Add waste before you round up: the 10% example is 62 bags of 80 lb.

When do bags cost more than ready-mix?

Compare whole bags times the bag price with ordered cubic yards times the plant price, plus any short-load fee. In the labeled example below, 56 bags at $6.50 is $364, while 1.5 yards at $160 plus a $75 short-load fee is $315. Those prices are hypothetical, not a quote.