Dry Pour Concrete Calculator
Size a dry-pour (pour-and-soak) concrete slab — enter your slab dimensions to get the number of 40, 60 or 80 lb bags you need to spread dry and then wet, plus an estimated cost.
United States — national average · 2026 prices
Material only unless stated as installed. Excludes tax, permits and local labour. Verify with local suppliers — see how we calculate.
How this calculator works
Every figure above comes from the formula below, applied to the assumptions listed. Nothing is looked up from a hidden table — you can reproduce the result by hand.
Formula
cubic feet = length × width × thickness (in) ÷ 12 × (1 + waste ÷ 100)
bags = cubic feet ÷ bag yield, rounded up (80 lb = 0.60 · 60 lb = 0.45 · 40 lb = 0.30)
Assumptions & limits
- The bag count for a dry pour is the same as for a mixed pour, because it is driven by the volume of the form — the method changes, the volume does not.
- Bag yields are the QUIKRETE Concrete Mix figures. A dry pour that is not fully hydrated will occupy the same space at lower strength, so the count is a purchase quantity, not a strength guarantee.
- Dry pour is treated as a light-duty, non-structural method. It reaches lower and less predictable strength than properly mixed concrete.
- Thickness above about 4 inches is hard to wet through — the usual dry-pour failure mode — so the count assumes a shallow slab.
Worked example
A 4 ft × 8 ft stepping-stone pad, 3 inches thick, 10% waste, 80 lb bags
- Cubic feet = 4 × 8 × 3 ÷ 12 = 8.0, plus 10% waste = 8.8 cu ft
- 80 lb bags = 8.8 ÷ 0.60 = 14.7 → 15 bags
- 60 lb bags = 8.8 ÷ 0.45 = 19.6 → 20 bags
Result:15 × 80 lb bags spread dry, screeded level, then misted in stages.
Built and maintained by Christoph Ballmer, Honeygoat GmbH
Method and constants last checked against the calculator code on August 17, 2026. Independent trade review is not yet in place for this calculator — see how we handle review.
Read the site-wide calculation methodology · estimate vs. quote and safety limits
What is dry pour concrete?
Dry pour — also called pour-and-soak — skips mixing: you spread dry concrete mix into a form, screed it level, then wet it down with a fine mist so it hydrates and sets in place. It's a popular DIY shortcut for small, light-duty slabs like garden pads, shed floors, walkways and stepping stones. Because it's based on the same volume as a normal pour, the bag count is the same — the calculator above sizes it from your slab dimensions.
bags = (length × width × thickness ÷ 12, in cu ft) ÷ bag yield
How to dry pour a slab
- Build and level a form, and compact the subgrade.
- Spread the dry mix and screed it to your thickness (most DIY slabs are 2–4 inches).
- Mist the surface evenly with a fine spray — soak it through without washing channels in it.
- Keep it damp while it cures over the next few days.
Dry pour works for non-structural slabs, but it generally reaches lower strength and cures less evenly than properly mixed concrete, so keep it to light-duty projects. For load-bearing work or a precise cost comparison, use the concrete calculator and the concrete cost calculator.
Where dry pour works — and where it does not
| Good fit | Wrong tool |
|---|---|
| Stepping stones, small pads | Driveways and anything carrying vehicles |
| Shed and AC-unit pads (light duty) | Structural slabs, footings, foundations |
| Fence-post surrounds (fast-setting mix) | Slabs thicker than ~4 inches |
| Garden edging and walkway sections | Anything an inspector will look at |
Common mistakes
- Going too thick. Water has to reach the bottom of the lift; beyond about 4 inches the core stays dry and powdery — the classic dry-pour failure.
- Flooding instead of misting. A hard stream carves channels and washes cement to the surface. Mist in stages: surface, wait, mist again — several rounds.
- Skipping the cure. Hydration needs days of moisture, not one wetting. Misting over the first days (or covering with plastic) is what brings the strength up.
- Expecting mixed-concrete strength. Even done well, dry pour cures less evenly than properly mixed concrete. Treat it as a convenience method for light duty.
- No reinforcement, no edge thought. Edges and corners crack first on thin pads — rounding edges and keeping pads small limits it.
For anything load-bearing, mix it: the concrete calculator sizes the same bags for a conventional pour, and past roughly a cubic yard the ready-mix comparison usually wins outright.
Bag counts here are purchase quantities based on volume — they say nothing about the strength a dry-pour slab reaches, which depends on the hydration you give it.
Frequently asked questions
What is dry pour concrete?
Dry pour (also called pour-and-soak) is a method where you spread dry concrete mix into a form, screed it level, and then wet it down with a fine mist so it hydrates and sets in place — skipping the usual mixing. It is popular for small DIY pads, walkways and stepping stones.
How many bags do I need for a dry pour slab?
The bag count is the same as a normal pour, since it is based on volume: spread enough dry mix to fill the form to your thickness. Using the standard yields (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 40 lb ≈ 0.30), the calculator works out how many bags to buy for your slab size.
Does dry pour concrete actually work?
Dry pour can work for light-duty, non-structural slabs like garden pads, shed floors and walkways, but it generally reaches lower strength and more uneven curing than properly mixed concrete. For anything load-bearing or structural, mixed concrete is the reliable choice. Treat dry pour as a convenience method for small projects.
What is the 4-2-1 rule for concrete?
It is the classic hand-mixing ratio by volume: 4 parts coarse aggregate, 2 parts sand, 1 part cement, which lands around 3,000 PSI. It matters here mainly as a contrast. Dry pour works with BAGGED mix precisely because the proportioning is already done at the plant - you are spreading a finished blend and letting water find it, so there is nothing to batch by eye. If you are mixing your own from separate materials, you are doing a wet pour, and the concrete calculator sizes that instead.
How many times do I water a dry pour concrete slab?
Enough times that the mix stays damp rather than a fixed number. The usual sequence is a thorough soaking with a fine mist at placement until water stops disappearing into the surface, another pass a few hours later, then keeping it damp for the next two to three days. Use a mist or shower setting throughout: a jet washes cement out of the surface and leaves a weak, dusty top layer. Hot, dry or windy weather means more frequent watering, cool damp weather less.
What does 1 yard of dry concrete weigh?
About 3,600 pounds as dry mix - a cubic yard takes roughly 45 of the 80 lb bags, and 45 x 80 = 3,600. Once it has taken up its water and cured, the same yard weighs closer to 4,050 pounds, because the water stays in the slab. Both figures are worth knowing for different reasons: the dry one is what your vehicle has to carry home, the cured one is what the ground underneath has to hold.
How thick should a dry pour slab be?
Most DIY dry-pour slabs are poured 2 to 4 inches thick. Thicker slabs are harder to wet all the way through, which is a common dry-pour failure point. The calculator lets you set the thickness so the bag count matches your plan.