Concrete Bag Calculator

Units:
Select shape
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Calculate bags needed for a rectangular slab, patio, pad, or driveway section.

Total length of slab Enter a valid length
Total width of slab Enter a valid width
Standard 4 in; driveway 6 in Enter a valid thickness
Inside diameter of tube/hole Enter a valid diameter
Depth below frost line Enter a valid depth
Number of posts or tubes Enter a valid quantity
Total run of footing Enter a valid length
Width of footing Enter a valid width
Depth of footing Enter a valid depth
Outside diameter of slab Enter a valid diameter
Standard 4 in; patio 4–6 in Enter a valid thickness
Total number of steps Enter valid steps
Stair width Enter a valid width
Height of each step Enter a valid rise
Depth of each tread Enter a valid run
Outside diameter of column Enter a valid diameter
Total height of column Enter a valid height
Total length of wall Enter a valid length
Height of wall Enter a valid height
Wall thickness Enter a valid thickness
Enter your known volume Enter a valid volume
Select volume unit

How to use this calculator

  1. Select Imperial (ft/in) or Metric (m/cm) using the toggle at the top.
  2. Choose the shape tab that matches your project: Slab, Post Hole, Footing, Round Slab, Stairs, Column, Wall, or Custom Volume.
  3. Enter your dimensions. Results update live as you type.
  4. Set your waste buffer — 10% is recommended for DIY; 5% for experienced contractors.
  5. Optionally enter a price per 80 lb bag to get a cost estimate.
  6. All three bag sizes (40/60/80 lb) are shown side by side — pick what works best for you.
  7. Click Download PDF for a branded, printable project report.

Recommendations

Bag size: 80 lb bags give the best value per cubic foot. For solo DIY, 60 lb bags are easier to manage. 40 lb bags suit small patch repairs.

Waste buffer: Always add at least 10% for DIY — spills and surface variation are common. Use 5% only if you are an experienced contractor pouring a precise form.

Ready-mix threshold: If your project exceeds 1 cubic yard (~45 × 80 lb bags), consider ordering ready-mix. Mixing that volume by hand risks cold joints and is exhausting.

Bag yields: 80 lb = 0.60 ft³ · 60 lb = 0.45 ft³ · 40 lb = 0.30 ft³. Always verify the yield printed on your specific bag label.

Curing: Keep freshly poured concrete moist for at least 7 days. Cover with plastic sheeting in hot or dry conditions. Do not pour below 40°F (4°C) or above 90°F (32°C) without special precautions.
Options
Optional — enables cost estimate
Extra material allowance
⚠ Ready-mix recommended: Your project requires over 1 cubic yard. Mixing this many bags by hand risks cold joints and is very labour-intensive. Contact a local ready-mix supplier for a more practical and cost-effective pour.
Formula used ▼
ShapeFormula (cu ft)
Slab / PadL(ft) × W(ft) × T(ft)
Post Holeπ × r² × Depth(ft) × qty
FootingL(ft) × W(ft) × D(ft)
Round Slabπ × r² × T(ft)
StairsRise(ft) × Run(ft) × [N(N+1)/2] × W(ft)
Columnπ × r² × H(ft)
WallL(ft) × H(ft) × T(ft)

Bags = CEIL(Volume ft³ ÷ yield). Yields: 80 lb = 0.60 ft³ · 60 lb = 0.45 ft³ · 40 lb = 0.30 ft³. 1 cu yd = 27 ft³. Waste = volume × (1 + %/100).

Tips & recommendations ▼

80 lb bags offer the best yield-to-cost ratio. Use 60 lb for solo work — easier to lift and mix single-handedly.

Cold joint warning: Mix and pour continuously. Concrete that begins to set before the next batch creates a structural weak point.

Curing: Keep freshly poured concrete moist for at least 7 days. Cover with plastic sheeting in hot or dry conditions.

Temperature: Do not pour below 40°F (4°C) or above 90°F (32°C) without special precautions.