Concrete Slab Calculator

Concrete Basics for Kentucky Homeowners

Concrete is sold by the cubic yard (27 cubic feet). Almost every outdoor structure UIR builds — deck footings, driveway approaches, shed pads, pole barn floors, retaining wall footings, and patio slabs — starts with a concrete calculation. Getting the volume right prevents two expensive problems: running short mid-pour (which creates a cold joint and weakens the slab) and over-ordering (which you pay for and don't use).

Bags vs. Ready-Mix Truck

For pours under about 0.5 cubic yards, mixing bags yourself (or having your contractor mix them) is practical. Above 0.5 yards, a ready-mix truck is almost always more economical and produces more consistent concrete. The typical minimum truck load is 1 cubic yard; short-load fees apply for small orders.

For a standard 20×20 patio at 4" depth, you're looking at approximately 4.9 cubic yards — well into truck territory. For a 10×10 shed pad at 4", you're at about 1.2 yards, right at the minimum truck load threshold.

Thickness Recommendations for Grayson County

Kentucky's freeze-thaw cycle is hard on concrete that's poured too thin. UIR's standard recommendations for Grayson County:

• Sidewalks and light paths: 3–4 inches, with wire mesh or rebar
• Residential patios: 4 inches minimum
• Driveways: 5–6 inches, with rebar on 18–24" grid
• Deck and fence footings: Per local code — typically 8–12" diameter, depth below frost line (24" minimum in Grayson County)
• Pole barn floors: 4–6 inches depending on use; 6" with wire mesh for vehicle storage

Footings and Frost Depth

Any footing that supports a structure — deck posts, pole barn posts, carport columns — must be set below the local frost line to prevent heave. Grayson County's frost depth is approximately 12–18 inches, but UIR pours all structural footings to at least 24 inches for margin. The concrete calculator above works for cylindrical post holes too — just calculate the volume for a circular cross-section using our post hole concrete calculator on the main tools page.

Reinforcement

Concrete is strong in compression but weak in tension — steel reinforcement handles the tension. For patios and driveways, 6×6 welded wire mesh or #3 rebar on an 18" grid is standard. For footings, UIR typically uses two #4 rebar horizontally with #3 vertical ties. Your building inspector will have the final word on structural footings.

Contact UIR for a free estimate on any concrete work in Grayson County, Leitchfield, Elizabethtown, or the Nolin Lake and Rough River Lake areas.