A 12x20 concrete patio (240 square feet) is a popular size for backyard entertaining, dining areas, and outdoor living spaces. This guide gives you the exact concrete calculation for a 12x20 patio at the standard 4-inch thickness, with ready-mix and bagged options, complete cost breakdown, base requirements, and professional installation advice to ensure your patio lasts decades.
The Short Answer
For a 12x20 patio at 4 inches thick:
- Concrete needed: 3.0 cubic yards (80 cubic feet)
- With 10% waste factor: 3.3 cubic yards
- Bags required (80-lb): 135 bags (without waste) or 149 bags (with waste)
- Ready-mix cost: $480-$600 (concrete only)
- Total project cost: $1,200-$2,400 (including base, labor, finishing)
Use our concrete calculator for other sizes and thicknesses.
Step-by-Step Calculation
Here's the exact math for a 12x20 patio-verify it yourself or adjust for your specific needs:
1. Basic Volume Formula
Volume (cubic feet) = Length (ft) x Width (ft) x Thickness (ft)
For a 12x20 patio at 4 inches thick:
- Length = 20 feet
- Width = 12 feet
- Thickness = 4 inches = 4 / 12 = 0.333 feet
- Calculation: 20 x 12 x 0.333 = 79.92 cubic feet (about80 cubic feet)
2. Convert to Cubic Yards
Concrete is ordered by the cubic yard (1 yard = 27 cubic feet).
Calculation: 80 / 27 = 2.96 cubic yards
Rounded up: 3.0 cubic yards (standard rounding for ordering).
3. Add Waste Factor
Patios need extra concrete for:
- Spillage during placement
- Uneven subgrade (patios often have slight slopes for drainage)
- Formwork variations
- Over-excavation at edges
Standard waste factor: 10% for patios (due to drainage slopes).
Calculation with 10% waste: 3.0 x 1.10 = 3.3 cubic yards
Final order: 3.3 cubic yards (often ordered as 3.5 yards for simplicity).
Bagged Concrete Option
For a 12x20 patio, bagged concrete is generally not recommended (too many bags, too much labor), but here's the math if you must:
Bagged Concrete Calculation
| Bag Size |
Yield per Bag |
Bags Needed (no waste) |
Bags Needed (10% waste) |
Total Cost |
| 60-lb bags |
0.45 cubic feet |
178 bags |
196 bags |
$890-$1,180 |
| 80-lb bags |
0.60 cubic feet |
135 bags |
149 bags |
$750-$1,000 |
| 90-lb bags |
0.675 cubic feet |
120 bags |
132 bags |
$800-$1,100 |
Reality check: 149 bags of 80-lb concrete weighs 11,920 pounds (nearly 6 tons). You'd need to mix 3-4 bags at a time, which would take 2-3 days of continuous work. Ready-mix is strongly recommended for patios this size.
Complete Project Cost Breakdown
A 12x20 patio involves multiple cost components. Here's a realistic 2026 budget:
Material Costs
| Item |
Quantity |
Cost Range |
Notes |
| Concrete (ready-mix) |
3.3 yards |
$495-$660 |
No short-load fee at this size |
| Gravel base |
6 tons |
$180-$300 |
4-6 inches compacted |
| Rebar or wire mesh |
240 sq ft |
$96-$192 |
Highly recommended for patios |
| Form lumber |
64 linear feet |
$50-$100 |
2x4s, stakes, screws |
| Tools & equipment rental |
2-3 days |
$100-$250 |
Plate compactor, power trowel, saw |
| Total materials (DIY) |
- |
$921-$1,502 |
Before labor |
Labor Costs
- DIY labor: Your time (typically 25-40 hours over 3-5 days)
- Professional installation: $6-$12 per square foot = $1,440-$2,880
- Finishing options: Broom finish (included), stamped (+$4-$8/sq ft), stained (+$2-$4/sq ft)
- Total professional project: $2,361-$4,382 (materials + labor)
Base Material Requirements
Patios need a stable, drainable base to prevent settling and frost damage. For a 12x20 patio:
Gravel Base Calculation
Standard base: 4-6 inches of compacted crushed stone (#57 or #304 gravel).
Volume needed: 20 x 12 x 0.333 = 80 cubic feet = 2.96 cubic yards
Weight needed: 2.96 x 1.35 = 4.0 tons (round up to 4-5 tons)
Cost: $200-$350 for 5 tons of crushed stone (delivered).
Patio-Specific Base Considerations
- Drainage slope: Patios need 2% slope away from house-adds 1/2-1 inch of extra thickness.
- Compaction: Rent a plate compactor-hand tamping won't achieve proper density.
- Fabric: Consider landscape fabric under gravel in areas with poor drainage.
- Edging: Patios often benefit from decorative concrete edging or restraint.
Patio-Specific Design Considerations
A 12x20 patio isn't just a slab-it's an outdoor living space. Consider these design elements:
Drainage & Slope
- Minimum slope: 2% (1/4 inch per foot)
- Total fall: 20 ft x 0.25"³/ft = 5 inches from back to front
- Volume increase: Adds 10-15% more concrete
- Key: Slope away from house foundation
Control Joints
- Spacing: Every 4-5 feet in both directions
- For 12x20: 3 joints lengthwise, 4-5 joints widthwise
- Depth: 1/4 of slab thickness (1 inch for 4-inch slab)
- Purpose: Control cracking in predictable lines
Finishing Options
- Broom finish: Standard, slip-resistant, included
- Stamped concrete: +$4-$8/sq ft, decorative
- Stained concrete: +$2-$4/sq ft, color options
- Exposed aggregate: +$3-$6/sq ft, textured
Common Variations & Adjustments
Not every 12x20 patio is the same. Here's how to adjust for different scenarios:
6-inch Thick Patio
- Volume: 20 x 12 x 0.5 = 120 cubic feet
- Cubic yards: 120 / 27 = 4.44 yards
- With waste: 4.88 yards (order 5 yards)
- Use case: Heavy furniture, hot tub pads, fire pit areas
Curved or Irregular Shape
- Waste factor: 15-20% instead of 10%
- Formwork: More complex, more lumber needed
- Calculation: Break into rectangles + triangles
- Example: 12x20 with curved edge = 3.5-3.75 yards
Integrated Features
- Fire pit pad: Add 1-2 yards for 4x4 or 6x6 pad
- Seating walls: Additional concrete for footings
- Steps: Calculate risers and treads separately
- Plan ahead: Pour features with main patio for monolithic strength
Professional Installation Timeline
A 12x20 patio requires careful planning and staging. Here's a realistic timeline:
Typical Project Schedule
- Day 1-2: Site preparation - Excavation, rough grading, base installation
- Day 3: Formwork & reinforcement - Build forms, install rebar/mesh, final grade
- Day 4: Concrete pour - Place, screed, bullfloat, edge, joint (morning work)
- Day 5: Finishing - Final troweling, curing, cleanup
- Day 6-12: Curing - Keep moist, protect from traffic
- Day 14+: Sealing (optional) - Apply sealer if desired
Pro tip: Schedule concrete delivery for early morning (7-9 AM) to avoid afternoon heat and have maximum working time.
Common Patio Mistakes to Avoid
Planning & Ordering Mistakes
- Under-ordering concrete: Running short on a patio means visible cold joints-ugly and weak.
- Ignoring drainage slope: Flat patio = water pooling = ice damage and staining.
- Wrong concrete mix: Using 3000-psi for a patio when 4000-psi with air entrainment is better for freeze-thaw areas.
- No expansion joint against house: Concrete expands and can crack foundation or patio.
Installation Mistakes
- Inadequate base: 2 inches of gravel instead of 6 leads to settling within a year.
- Poor compaction: Hand-tamped base settles unevenly under concrete weight.
- Finishing too early: Working bleed water back into surface causes dusting and scaling.
- No control joints: Concrete cracks randomly instead of at planned locations.
Curing & Maintenance Mistakes
- Letting patio dry too fast: Not keeping moist for 7 days reduces strength by 30-50%.
- Heavy traffic too soon: Furniture or vehicles on patio before 28-day full cure.
- Wrong sealer application: Sealing before concrete fully cures (wait 28 days).
- No winter protection in cold climates: De-icers with ammonium or magnesium damage concrete.
Calculator vs. Manual Calculation
While this guide gives you exact numbers for a standard 12x20 patio, real projects often have variables:
When to Use Our Concrete Calculator
- Your patio isn't exactly 12x20 (common sizes: 10x20, 14x20, 12x24, etc.)
- Different thickness (3", 5", 6", etc.)
- Multiple slopes or levels (terraced patio, steps integrated)
- Want to compare bagged vs. ready-mix costs and practicality
- Need to calculate base materials at the same time
Our concrete calculator handles all these variables instantly. Enter your exact dimensions, select thickness, add slope percentage, and get precise cubic yards with waste factor already included.
Next Steps for Your 12x20 Patio
Now that you know exactly how much concrete you need:
- Verify site dimensions-measure twice, allowing for formwork thickness.
- Determine slope requirements-2% minimum away from structures.
- Calculate base materials using our gravel calculator.
- Get 2-3 local quotes for concrete delivery-prices vary 20-30%.
- Schedule wisely-avoid extreme temperatures, rain, or high winds.
- Prep helpers and tools-you need 3-4 people for a pour this size.
- Have contingency plan-extra lumber, tarps, and know what to do with leftover concrete.
Final contractor advice: Order 10-15% more concrete than calculated. For a 12x20 patio, order 3.5 yards instead of 3.3 yards. The extra 0.2 yards (about $30-$40) is cheap insurance. Use leftover concrete for stepping stones, bench footings, or decorative pieces rather than wasting it.
Ready to Calculate Your Exact Patio Needs?
Use our free Concrete Calculator for precise measurements tailored to your specific patio design. Enter any dimensions, thickness, slope, and waste factor for instant cubic yards and cost estimates.
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