About this calculator
Dry pouring (or "pour-and-soak") means dumping bagged concrete mix into your forms dry, screeding it level, then wetting it with a fine spray over a few hours instead of mixing first. This calculator gives you the bag count to buy — enter the slab's length, width, and thickness, pick a bag size, and it sizes the order with a waste allowance. Before you start, it's worth knowing whether dry pouring is right for your project: it's fine for small, non-structural pads but weaker than properly mixed concrete — the guide below breaks down when it works and when to mix wet instead.
How the math works
Dry pour uses the same volume math as any slab: length × width × thickness in feet gives cubic feet, divided by the bag's yield (an 80 lb bag ≈ 0.60 cu ft, a 60 lb ≈ 0.45, a 40 lb ≈ 0.30) and rounded up, with a waste allowance added. There's no mixing step, so the bag count is the whole material list — but the trade-off is less control over water and strength, which is why dry pour is best kept to thin, small, non-structural pours.
Common questions
Does dry pour concrete actually work?
For small, non-structural pours — stepping stones, a shed-corner pad, fence-post collars — yes, well enough. It cures weaker and less evenly than mixed concrete, so it's not for driveways, footings, or anything load-bearing or reinforced. The dry pour guide linked below covers the full pros and cons.
How many bags do I need to dry-pour a slab?
It's the same volume math as any pour. A 6×6 ft pad at 4" is about 12 cubic feet — roughly 22 eighty-pound bags with a waste allowance. Enter your own dimensions above for an exact count.
How thick can you dry pour concrete?
Keep it thin — about 2 to 4 inches. Water has to soak all the way through to hydrate the mix, and thicker dry pours tend to stay powdery and weak in the middle.