Masonry & Concrete

Concrete Slab & Footing Calculator

Calculate total cubic yards of ready-mix concrete, the exact number of 80 lb or 60 lb bags needed, and estimate your total material budget based on current US retail prices.

Length (Feet)

Width (Feet)

Thickness (Inches)

Jobsite Waste & Settling Factor

Avg. Price per 80 lb Bag ($ USD)

Avg. Ready-Mix Truck Price / Yard ($)

Total Ready-Mix Volume 1.63 Cubic Yards (yd³)

80 lb Bags Needed 74 bags 0.60 cu ft per bag yield

60 lb Bags Needed 98 bags 0.45 cu ft per bag yield

Total Surface Area 120 sq ft Length × Width footprint

Estimated Material Budget

Estimated Project Cost Comparison

Option 1: Bagged Concrete (DIY Mixing) $432.90 Based on 74 bags @ $5.85/bag

                            Option 2: Ready-Mix Delivery Truck
                            $236.35
                            Based on 1.63 yd³ @ $145/yd³ (plus local short-load fees if <4 yd³)
                        

💡 Jobsite Rule of Thumb: When your project exceeds 1.5 to 2.0 cubic yards, hand-mixing 70+ bags in a wheelbarrow becomes exhausting and risks cold joints. Calling a local ready-mix concrete batch plant usually saves significant labor time.

📐 Cross-Section Blueprint: Standard Floating Slab Spec ACI 318 / IRC R506

Cured Ready-Mix Concrete (3,000–4,000 PSI)

Steel Reinforcement (Mid-depth on rebar chairs)

6-Mil Polyethylene Vapor Barrier

4" Crushed Stone / Pea Gravel Base

How to Accurately Estimate Concrete for Slabs & Footings

Pouring a concrete slab for a patio, sidewalk, garage floor, or storage shed requires precision. Ordering too little concrete leads to cold joints (weak structural seams where wet concrete meets hardening concrete), while ordering too much wastes money.

The Standard Cubic Yard Formula

In standard US construction, ready-mix concrete is sold by the cubic yard (yd³), which equals exactly 27 cubic feet. To calculate volume:

Cubic Yards = (Length in Feet × Width in Feet × Thickness in Feet) ÷ 27

Because slab thickness is measured in inches, divide your thickness by 12 first. For example, a 4-inch slab is 4 / 12 = 0.333 feet thick.

Bag Yields: 80 lb vs 60 lb Pre-Mixed Bags

80-pound bag: Yields approximately 0.60 cubic feet of cured concrete. You need 45 bags to make 1 cubic yard.
60-pound bag: Yields approximately 0.45 cubic feet. You need 60 bags to make 1 cubic yard.
50-pound bag: Yields approximately 0.375 cubic feet. You need 72 bags to make 1 cubic yard.