Calculate exactly how much concrete you need — slabs, footings, columns, steps, and tube forms. Get cubic yards, cubic feet, bag count, and estimated cost in seconds. The most accurate concrete yardage calculator, used by contractors and DIYers.
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This concrete calculator uses formulas from current industry standards. Volume for rectangular shapes uses L x W x D / 27 (cubic yards). Cylinders use π x r² x H / 27. Stairs use stair-volume accumulation (each step adds one riser-height of depth to the solid block). Bag counts use PCA published yields: 0.60 ft³ per 80-lb bag, 0.45 ft³ per 60-lb bag, 0.30 ft³ per 40-lb bag.
Whether you're pouring a concrete slab for a patio, calculating concrete yardage for a driveway, figuring out how many bags of concrete to buy for post holes, or estimating a footing for a foundation — every calculation starts the same way: find the volume, then convert to the unit your supplier uses.
Concrete is sold by the cubic yard from ready-mix companies, and by the bag from home improvement stores. One cubic yard = 27 cubic feet. To calculate how much concrete you need for a slab:
Volume (cu ft) = Length (ft) x Width (ft) x Thickness (in) / 12
Volume (cu yd) = Volume (cu ft) / 27
Always add 10% waste: Order = Calculated volume x 1.10
Example: 12 x 16 ft patio, 4" thick = (12 x 16 x 0.333) / 27 = 2.37 cu yd
Order quantity = 2.37 x 1.10 = 2.6 cubic yards
For smaller projects — post holes, steps, small slabs — pre-mixed bags are more practical than ordering a ready-mix truck. The three standard bag sizes have different yields:
| Bag Size | Yield (cu ft) | Bags per Cu Yd | Best For |
|---|---|---|---|
| 80 lb | 0.60 cu ft | 45 bags | Footings, slabs, post holes |
| 60 lb | 0.45 cu ft | 60 bags | Steps, walls, general use |
| 40 lb | 0.30 cu ft | 90 bags | Small repairs, decorative work |
Foundation footings support the structural load of a building. Continuous (strip) footings run around the perimeter. Isolated (pad) footings support individual columns. The footing width must be at least twice the wall thickness, and depth must reach below the frost line in your area (ranging from 12 inches in the Deep South to 60 inches in Minnesota).
Strip footing: Volume (cu yd) = Length (ft) x Width (ft) x Depth (ft) / 27
Round pad footing: Volume = pi x (Diameter/2)^2 x Depth / 27
Example strip: 40 ft run, 12" wide, 12" deep = (40 x 1 x 1) / 27 = 1.48 cu yd
Post holes and column forms use cylindrical volume. Quikrete and Sakrete tube forms come in 6, 8, 10, and 12-inch diameters. The fast-setting concrete varieties (Quikrete Fast-Setting 50-lb) can be poured dry directly into the hole, which is ideal for fence posts and deck footings where one bag fills approximately 1/3 of a 10-inch diameter x 24-inch deep hole.
A concrete driveway must be thick enough to support vehicle loads without cracking. Residential driveways (passenger cars) need a minimum of 4 inches, with 5 to 6 inches recommended. Driveways that will receive heavy truck traffic — delivery trucks, RVs — need 6 inches minimum. Control joints should be cut every 8 to 12 feet to manage cracking.
| Application | Min Thickness | Recommended | Concrete PSI |
|---|---|---|---|
| Sidewalk / walkway | 3 in | 4 in | 3,000 PSI |
| Residential driveway | 4 in | 5-6 in | 4,000 PSI |
| Garage floor / slab | 4 in | 5-6 in | 4,000 PSI |
| Heavy truck driveway | 6 in | 7-8 in | 4,500 PSI |
| Structural slab | 5 in | 6-8 in | 4,000-5,000 PSI |
| Post holes (deck footings) | — | 2x post diameter | 3,000 PSI |
| Concrete steps | 4 in | 6 in | 4,000 PSI |
Ready-mix concrete typically costs $120 to $200 per cubic yard in 2026, depending on your region, mix design, and delivery distance. Specialty mixes (high-strength, fiber-reinforced, colored) add $20 to $80 per yard. Short-load fees for less than a full truck add $50 to $200. For bag concrete, 80-lb bags run $6 to $9 each at major retailers — equivalent to $270 to $405 per cubic yard when buying bags, which is why ready-mix is more economical for larger pours.
| Slab Size | 4" Thick | 6" Thick | 80-lb Bags (4") |
|---|---|---|---|
| 10 x 10 ft | 1.23 cu yd | 1.85 cu yd | 56 bags |
| 12 x 12 ft | 1.78 cu yd | 2.67 cu yd | 80 bags |
| 10 x 20 ft | 2.47 cu yd | 3.70 cu yd | 111 bags |
| 20 x 20 ft | 4.94 cu yd | 7.41 cu yd | 222 bags |
| 24 x 24 ft | 7.11 cu yd | 10.67 cu yd | 320 bags |
| 30 x 40 ft (driveway) | 14.81 cu yd | 22.22 cu yd | 667 bags |
When mixing concrete on site from raw materials (for large projects without truck access), the standard 1:2:3 ratio means 1 part Portland cement, 2 parts clean sharp sand, and 3 parts coarse aggregate (3/4 inch crushed stone) by volume, plus water. The water-to-cement ratio should be 0.45 to 0.55 — start with less water and add gradually. Too much water is the single biggest cause of weak concrete: every extra gallon of water per yard reduces strength by approximately 200 PSI.
Concrete gains strength over 28 days. At 24 hours, you can walk on it carefully. At 3 days, it reaches about 40% strength. At 7 days, 70% — safe for vehicle traffic on driveways. Full design strength (typically 3,000 to 4,000 PSI) is reached at 28 days. Keep new concrete moist during curing (wet burlap, plastic sheeting, or curing compound) to prevent surface cracking and achieve full strength. Avoid pouring concrete when temperatures are below 40°F or above 90°F without special precautions.