Concrete Slab Calculator: Cubic Yards, Bags, Rebar & Cost

Q: How many bags of concrete do I need for a 10x10 or 16x20 slab?

One 80-pound bag of pre-mixed concrete yields approximately 0.60 cubic feet, while a 60-pound bag yields 0.45 cubic feet. A 10x10 slab at 4 inches thick (36 cu ft with 8% waste) requires 60 bags (80 lb) or 80 bags (60 lb). A 16x20 slab at 4 inches thick (115.2 cu ft with waste) requires 193 bags (80 lb), making a 4.27-cubic-yard ready-mix truck delivery far more practical.

Q: At what slab size is a ready-mix concrete truck cheaper than buying bags?

Once your project exceeds 1.5 to 2.0 cubic yards (roughly 68 to 90 eighty-pound bags, or a 10x12 slab at 4 inches thick), ordering a ready-mix transit truck is almost always cheaper—even after paying a $125 to $200 short-load delivery fee.

Q: How thick should a concrete slab be for a patio vs. a garage or driveway?

For pedestrian loads such as backyard patios, sidewalks, and hot tub pads, a 4-inch concrete slab over 4 inches of compacted crushed stone is standard. For passenger car driveways and residential garage floors, pour a 5-inch to 6-inch slab with #4 rebar on 18-inch centers. For heavy pickup trucks or RV pads, use a 6-inch slab of 4,000+ PSI concrete with a 12-inch thickened perimeter edge.

● Interactive 5-Layer Structural Concrete Slab Blueprint

Concrete Slab Calculator: Cubic Yards, 80-Lb Bags, Rebar & Cost

Tap any structural horizon on the blueprint below to calculate exact ready-mix cubic yards, pre-mixed bags, thickened edge footings, rebar grid, and pour cost.

1. Slab Dimensions 320 sq ft

Length (ft)

Width (ft)

Depth (in)

4″ for patios/walkways; 5″–6″ for driveways & garage slabs.

2. Concrete Mix PSI & Grade

Higher PSI resists freeze-thaw spalling and heavy axle loads.

3. Steel Reinforcement Grid

Calculates 20-ft rebar sticks or 5×10 wire mesh sheets.

4. Spillage Waste & Labor Mode 8% Buffer

0% (Exact) 8% (Standard) 15% (Uneven Grade)

Interactive Concrete Slab Cross-Section Blueprint (Tap Any Layer)

Surface Finish Concrete Slab Rebar/Mesh Gravel Base

Add 12″×12″ Thickened Monolithic Edge Footing Include 4″ Compacted Crushed Stone Sub-Base Include 10-Mil Vapor Barrier & Perimeter Form Lumber Include Concrete Line Pump / Buggy Rental (+$325)

Active Structural Horizon: 2. Poured Concrete Slab Horizon Click below to customize this zone:

CONCRETE SLAB ESTIMATE SUMMARY $8.66 / sq ft installed

Concrete Volume Needed

4.27 Cu Yds

115.2 Cu Ft • 193 Bags (80 lb)

Estimated Project Total

$2,772

Range: $2,356 – $3,271

Ready-Mix Concrete or Pre-Mix Bags (4.27 yd³ @ 3,500 PSI) $705

Forming, Pouring & Finishing Labor (Pro Finisher Crew) $1,184

Steel Rebar Grid & Gravel Sub-Base (24 Sticks + 6.1T Base) $667

Vapor Barrier, Forms & Surface Sealer (72 lf Forms + Seal) $216

5. Ready-Mix Truck vs. Pre-Mix Bags & Weight Analyzer ✓ Ready-Mix Truck Saves $412

60-lb / 80-lb Bags 256 / 193 Bags

Rebar / Mesh Qty 24 Sticks (20′)

Total Slab Weight 17,280 Lbs

💡 Structural Concrete Ordering Verdict: Loading concrete slab engineering analysis…

Itemized Layer-by-Layer Concrete Slab Material & Cost Sheet

Complete bill of materials with cubic yards, 80-lb bag counts, rebar sticks, crushed gravel tons, and labor breakdown

5 Structural Horizons Calculated

Blueprint Horizon	Structural Specification	Volume / Area	Units / Bag Equiv	Total Weight	Unit Rate	Est. Cost	Inspect

Related Concrete Coatings, Patio Comparisons & Basement Remodeling Tools

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Patio & Driveway Choice

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Deciding between pouring a monolithic stamped concrete slab versus laying interlocking pavers? Compare cracking risk, freeze-thaw longevity, and installed cost per square foot.

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Garage & Patio Coatings

Encore Concrete Coatings Review

Protecting a newly cured garage slab, pool deck, or patio? See how polyurea and epoxy floor coatings prevent road salt pitting, hot-tire pickup, and oil stains.

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Interior Renovation Budget

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About This Interactive Concrete Slab Calculator: Key Engineering Features

Ordering concrete is one of the most unforgiving steps in residential construction: ordering half a cubic yard too little leaves a cold joint in your patio or garage floor, while paying short-load fees or mixing 150 heavy bags by hand wastes time and money. Our interactive concrete slab calculator combines a precision concrete yard calculator with an itemized concrete slab estimator so homeowners, DIYers, and flatwork contractors can calculate exact cubic yards, 60-lb and 80-lb pre-mix bag counts, thickened perimeter edge footings, rebar grids, and compacted gravel base requirements.

1. Monolithic Thickened Edge & Yardage Engine

Standard flat calculators ignore the thickened 12″×12″ perimeter turndown beam required for garage slabs, sheds, and driveways. Our concrete yard calculator computes both the main field slab and perimeter edge footing volume automatically.

2. Interactive 5-Layer Structural Blueprint

Click directly on any structural horizon in the SVG cross-section—Surface Finish & Coating, Poured Concrete Slab, Rebar & Wire Mesh Grid, Compacted Crushed Stone Sub-Base, or Vapor Barrier & Forms—to customize PSI strength and finishing styles.

3. Ready-Mix Truck vs. 80-Lb Bag Cost Optimizer

Compares delivered ready-mix transit truck pricing (including short-load delivery fees for pours under 4 cubic yards) against palletized 80-lb pre-mixed bags, while calculating exact 20-foot rebar sticks and control joint saw-cut spacing.

How to Use This Concrete Slab Estimator (Step-by-Step)

Step 1: Enter Slab Length, Width & Thickness Input your slab Length and Width in feet and your target Depth in inches (4 inches for standard patios/sidewalks; 5 to 6 inches for driveways, RV pads, and garage floors).

Step 2: Choose Concrete PSI Grade & Steel Reinforcement Select between 3,000 PSI, 3,500 PSI, 4,000 PSI, or 4,500 PSI fiber-reinforced mix, and pick #4 rebar on 18″ or 12″ centers or 6×6 wire mesh sheets.

Step 3: Tap Blueprint Layers to Add Footings, Base & Finishes Click Layer 1 on the blueprint to compare broom finish vs. stamped concrete or polyurea floor coatings. Toggle the checkboxes to include a 12″×12″ thickened edge footing, 4″ gravel base, or line pump rental.

Step 4: Compare Pro vs. DIY Costs & Print Your Pour Sheet Switch between Turnkey Finisher Crew, DIY with Ready-Mix Truck, or 100% DIY Bagged Mix. Click “Copy Pour Estimate” or “Print / PDF” to save your itemized bill of materials.

Core Formula: How Our Concrete Yard Calculator & Cost Estimator Works

To convert slab dimensions into cubic yards, divide your slab thickness in inches by 12 to get feet, multiply Length (ft) × Width (ft) × Depth (ft) to find cubic feet, and divide by 27 (since 1 cubic yard equals 27 cubic feet). Always add a 5% to 10% spillage and subgrade unevenness buffer. For example, a 20×16-foot patio poured 4 inches thick equals 320 × 0.333 = 106.7 cubic feet (3.95 cubic yards), or 4.27 cubic yards with an 8% buffer. When using our tool as a concrete slab cost calculato, standard turnkey installation averages $6.50 to $12.00 per square foot ($2,080 to $3,840 for a 320 sq ft patio), breaking down into roughly $155 to $195 per cubic yard for ready-mix concrete, $1.25 to $2.50 per sq ft for gravel base and rebar, and $3.50 to $7.00 per sq ft for forming and finishing labor.

Frequently Asked Questions (Concrete Slab Volume, Bags & Site Prep)

How many bags of concrete do I need for a 10×10 or 16×20 slab? +

One 80-pound bag of pre-mixed concrete yields approximately 0.60 cubic feet, while a 60-pound bag yields 0.45 cubic feet. A 10×10 slab at 4 inches thick (36 cu ft with 8% waste) requires 60 bags (80 lb) or 80 bags (60 lb). A 16×20 slab at 4 inches thick (115.2 cu ft with waste) requires 193 bags (80 lb)—which weighs over 15,400 pounds, making a 4.27-cubic-yard ready-mix truck delivery far more practical and economical.

At what slab size is a ready-mix concrete truck cheaper than buying bags? +

Once your project exceeds 1.5 to 2.0 cubic yards (roughly 68 to 90 eighty-pound bags, or a 10×12 slab at 4 inches thick), ordering a ready-mix transit truck is almost always cheaper—even after paying a $125 to $200 short-load delivery fee. Furthermore, truck-batched concrete provides a monolithic, uniform cure that is impossible to match when mixing 90+ batches one wheelbarrow at a time.

Do I need to clear yard leaves before pouring a patio slab, and how much for leaf removal? +

Yes—building codes strictly prohibit pouring concrete or compacting gravel sub-base over organic matter, grass, or fallen leaves, because decomposing leaves create hollow voids that cause the slab to settle and crack. Furthermore, overhanging trees dropping leaves onto wet concrete will stain the fresh finish. If you are prepping a wooded backyard site in autumn and wondering how much for leaf removal before excavation begins, professional yard leaf clearing typically costs $200 to $450 for a standard lot (or $5 to $8 per bag) and ensures a clean, stable subgrade.

How thick should a concrete slab be for a patio vs. a garage or driveway? +

For pedestrian loads such as backyard patios, sidewalks, and hot tub pads, a 4-inch concrete slab over 4 inches of compacted crushed stone is standard. For passenger car driveways and residential garage floors, pour a 5-inch to 6-inch slab with #4 rebar on 18-inch centers. For heavy pickup trucks, boat trailers, or RV pads, use a 6-inch slab of 4,000+ PSI concrete with a 12-inch thickened perimeter edge.