How thick should a concrete slab be?

Standard residential slabs are 4 inches thick. Driveways and garages need 5-6 inches if heavy vehicles will park on them. Footings for walls typically require 8-12 inches.

How much extra concrete should I order?

Order 5-10% extra to account for uneven ground, spillage, and slight over-excavation. For complex shapes, go with 10-15%. Running short mid-pour creates a cold joint that weakens the structure.

How many bags of concrete per cubic yard?

One cubic yard requires approximately 45 bags of 80-lb concrete or 60 bags of 60-lb concrete.

Concrete Calculator — Yards, Bags, and Cost

Slab Thickness Guide

Application	Minimum Thickness	Recommended
Sidewalk (foot traffic)	3.5 inches	4 inches
Patio	4 inches	4 inches
Driveway (passenger cars)	4 inches	5 inches
Garage floor	4 inches	5–6 inches
Driveway (heavy trucks)	5 inches	6 inches
Foundation footing	8 inches	10–12 inches

Bag Concrete vs. Ready-Mix

For projects under 1 cubic yard, bag concrete (60 or 80 lb bags mixed by hand or in a portable mixer) is practical. Above 1 yard, ready-mix delivery almost always makes more sense — it's faster, more consistent, and often cheaper per yard. A typical ready-mix truck carries 8–10 cubic yards. Most suppliers have a minimum order of 1 yard with a short-load fee for orders under their minimum.

Curing Time

Concrete reaches 50% strength in 3 days and about 70% by day 7. Full 28-day strength is the standard benchmark. You can walk on a slab after 24-48 hours. Drive on a driveway after 7 days minimum. Keep concrete moist for the first 7 days — cover with plastic sheeting or use a curing compound. Temperatures below 50°F slow curing significantly; below 25°F, use heated enclosures or cold-weather admixtures.

How to Use This Concrete Calculator

Enter the length, width, and depth of the area to be poured. The calculator estimates cubic yards of concrete needed and number of bags (60 lb or 80 lb).

Formula & How It Works

Volume = Length × Width × Depth (convert all to feet). Cubic Yards = Volume (cu ft) / 27. Add 10% for waste. One 80-lb bag = 0.6 cu ft, one 60-lb bag = 0.45 cu ft.

Calculation Example

Patio 12 ft × 10 ft × 4 inches deep: Volume = 12 × 10 × 0.333 = 40 cu ft = 1.48 cubic yards. With 10% waste: order 1.63 yards (or 67 bags of 80-lb mix).

Expert Tips

Always order 10% extra — running short mid-pour creates a weak cold joint. For slabs, the minimum recommended thickness is 4 inches. Wire mesh or rebar adds structural integrity.

Concrete Calculator

Slab Thickness Guide

Bag Concrete vs. Ready-Mix

Curing Time

FAQ

Square Footage

Unit Converter

Paint Calculator

How to Use This Concrete Calculator

Formula & How It Works

Calculation Example

Expert Tips