Yards & Cost Estimator
Last reviewed: May 2026
Accurate concrete estimation prevents two expensive mistakes: ordering too little (which causes a cold joint if a second delivery is needed) and ordering too much (which wastes money and creates disposal problems).[1] This calculator computes cubic yards from your slab dimensions and thickness, adding the recommended waste factor. For related calculations, see the Concrete Calculator.
| Application | Thickness | Reinforcement | Cost per Sq Ft |
|---|---|---|---|
| Sidewalk | 4″ | Wire mesh | $6–$8 |
| Patio | 4″ | Wire mesh | $7–$10 |
| Residential driveway | 4–6″ | Rebar #4 @ 18″ | $8–$12 |
| Garage floor | 4–6″ | Rebar #4 @ 18″ | $7–$10 |
| Basement floor | 3.5–4″ | Wire mesh + vapor barrier | $6–$9 |
| Commercial floor | 5–8″ | Rebar #5 @ 12″ | $10–$18 |
| Application | Thickness | Concrete Strength | Reinforcement |
|---|---|---|---|
| Sidewalk / path | 4 inches | 3,000 PSI | Wire mesh or fiber |
| Patio / pool deck | 4 inches | 3,500 PSI | Wire mesh or #3 rebar @ 18" |
| Residential garage | 4–6 inches | 4,000 PSI | #4 rebar @ 12–18" |
| Workshop / heavy use | 5–6 inches | 4,000 PSI | #4 rebar @ 12" |
| Commercial / industrial | 6–8 inches | 4,500–5,000 PSI | #5 rebar @ 12" both directions |
The formula is straightforward: Volume (cubic yards) = (Length × Width × Thickness in feet) ÷ 27. For a 24×24-foot garage slab at 5 inches thick: (24 × 24 × 0.417) ÷ 27 = 8.9 cubic yards. Always add 5–10% for waste, uneven subgrade, spillage, and slight thickness variations — order 9.5–10 yards for this example. For irregular shapes, divide the area into rectangles and calculate each separately. Thickened edges (common at garage door openings and perimeter footings) require additional volume — a 12-inch-deep by 12-inch-wide thickened edge around a 24×24 slab adds approximately 1.5 cubic yards. Ready-mix concrete costs $120–$180 per cubic yard delivered, making the total material cost for a typical garage slab $1,200–$1,800. Professional installation (forming, pouring, finishing) adds $4–$8 per square foot in labor.
The subgrade — the soil beneath the slab — determines long-term slab performance more than any other single factor. Proper preparation includes removing topsoil and organic material (which decomposes and settles), compacting the native soil to 95%+ density, and placing 4–6 inches of compacted gravel as a capillary break and drainage layer. A 6-mil polyethylene vapor barrier over the gravel prevents ground moisture from migrating through the slab — essential for any enclosed space (garages, workshops, living areas) to prevent moisture damage to flooring, equipment, and stored items. Failing to compact the subgrade or remove organic material leads to differential settlement — some areas of the slab sink while others remain stable, creating cracks that are expensive to repair and impossible to fully reverse.
Concrete will crack — the goal is controlling where and how it cracks. Control joints (also called contraction joints) are intentional weakened planes cut or tooled into the slab surface, typically 1/4 to 1/3 of the slab depth. These joints create predetermined crack locations, ensuring that the inevitable shrinkage cracking occurs in straight, planned lines rather than random patterns. The rule of thumb for joint spacing: the distance between joints in feet should not exceed 2–3 times the slab thickness in inches. A 4-inch slab should have joints every 8–12 feet; a 6-inch slab every 12–18 feet. Joints should be cut within 6–18 hours of the pour (before shrinkage cracking begins) using a concrete saw with a diamond blade. Fiber reinforcement (synthetic or steel fibers mixed into the concrete) helps control minor surface cracking between control joints but does not replace structural rebar for load-bearing applications. See our Rebar Calculator for reinforcement planning and our Concrete Calculator for general concrete volume estimates.
Ready-mix concrete is specified by compressive strength (measured in PSI at 28 days), slump (a measure of workability — higher slump means more fluid concrete), and maximum aggregate size. Standard residential slab mixes use 3,500–4,000 PSI with a 4-inch slump and 3/4-inch aggregate. Admixtures modify concrete properties for specific conditions: water reducers increase strength without adding water, accelerators speed set time in cold weather, retarders slow set time in hot weather (preventing the concrete from setting before finishing is complete), and air-entraining agents create microscopic bubbles that improve freeze-thaw resistance — required by code in all exterior concrete in cold climates. Fiber admixtures (synthetic or steel) reduce shrinkage cracking. Specifying the right mix saves money and prevents problems: ordering 5,000 PSI concrete for a patio wastes $15–$25 per yard on unnecessary strength, while ordering 3,000 PSI for a garage floor may not meet code requirements for vehicle loading.
Concrete does not "dry" — it cures through a chemical hydration process that requires moisture and time. Proper curing is the single most important factor in achieving the specified strength and durability. Freshly poured concrete should be kept moist for a minimum of 7 days (28 days for maximum strength development) through one of several methods: spray-on curing compound (most common for slabs), wet burlap covered with polyethylene sheeting, or continuous water misting. Concrete that dries too quickly develops surface cracking, reduced strength (potentially 30–50% weaker than properly cured concrete), and increased permeability to water and chemicals. Avoid pouring when temperatures will drop below 50°F within 48 hours, as cold slows hydration and freezing before initial set destroys the concrete structure. In hot weather, schedule pours for early morning, use chilled mix water, and begin curing immediately after finishing. In cold weather, use insulating blankets over the fresh slab and consider ordering concrete with an accelerating admixture that speeds the initial set. The difference between a properly cured slab and a poorly cured one is visible within months — properly cured slabs maintain their smooth finish and resist surface dusting, while poorly cured slabs develop a powdery surface, increased porosity, and accelerated wear under traffic. Always plan curing materials and methods before the pour day — once concrete is placed, there is no time to acquire supplies. Concrete that reaches its full 28-day design strength through proper curing will outperform under-cured concrete of a higher specified strength, making curing the most impactful quality control step in any concrete project. Our Gravel Calculator estimates the base material needed beneath your slab, and our Rebar Calculator handles reinforcement planning for your structural concrete elements.
→ Always round up. It is far better to have a little extra than to run short mid-pour.[1]
→ Use 4 inches minimum for foot traffic. 3.5 inches is the absolute minimum for any load-bearing slab.[2]
→ Order 10% extra. Uneven subgrade, spillage, and form bulging consume material.
→ Sub-base matters. 4-6 inches of compacted gravel under the slab prevents cracking and settling.
See also: Concrete · Gravel · Square Footage · Deck