How to Calculate Concrete for a Patio (Step-by-Step Contractor Guide)

After pouring concrete patios for over 20 years, I’ve learned that the difference between a smooth job and a costly headache often comes down to one thing: accurate concrete calculations. Nothing’s worse than running short on a Saturday pour or over-ordering by two yards and watching your profit margin disappear.

I’m Brad, and I’ve poured everything from simple 10×12 slabs to complex curved patios with multiple levels. In this guide, I’ll walk you through exactly how to calculate concrete for a patio—the same methods I use on every job.

Whether you’re a homeowner planning a DIY project or a contractor looking to sharpen your estimating skills, this step-by-step guide will show you how much concrete you need for a patio, how to account for waste, and which mistakes to avoid.

Why Accurate Concrete Calculations Matter

Let me tell you what happens when you get it wrong:

Order too little: Your pour gets interrupted, you get cold joints (weak spots), and you’re scrambling to find more ready-mix on short notice—usually at premium prices.
Order too much: You’re paying $125-150 per cubic yard for material you’ll literally dump somewhere. That’s money straight out of your pocket.

I’ve seen both scenarios dozens of times. The goal is to order just enough concrete with a reasonable buffer for waste. That’s exactly what this guide will teach you.

Understanding Concrete Measurement Basics

Before we dive into calculations, let’s cover the fundamentals.

The Standard Unit: Cubic Yards

Concrete is ordered in cubic yards (often written as “yards” in the industry). One cubic yard equals:

27 cubic feet
A space 3 feet × 3 feet × 3 feet

Most ready-mix trucks carry 8-10 yards, and you’ll typically pay per yard delivered.

Standard Patio Thickness

For residential patios, 4 inches is the industry standard thickness. Here’s when I adjust:

3 inches: Only for small, non-structural pads (not recommended for patios)
4 inches: Standard residential patios with proper sub-base
5-6 inches: Heavy-duty applications, poor soil conditions, or driveways

For this guide, I’ll use 4 inches as the default, but I’ll show you how to adjust for any thickness.

Step-by-Step: How to Calculate Concrete for a Rectangular Patio

Let’s start with the most common scenario: a simple rectangular patio.

Step 1: Measure the Area

You’ll need:

A tape measure (I prefer a 25-foot for patios)
Helper (makes measuring much easier)
Paper and pen (or your phone calculator)

Measure the length and width in feet. Be precise—round to the nearest inch and convert to decimals.

Example: You’re pouring a 12×16 foot patio.

Step 2: Calculate Square Footage

Multiply length × width.

Formula: Length (ft) × Width (ft) = Square Footage

Example: 12 ft × 16 ft = 192 square feet

Pro Tip: Use our square footage calculator to double-check your math, especially on larger or irregular areas.

Step 3: Convert Thickness to Feet

Since we’ll calculate cubic feet, convert your thickness from inches to feet by dividing by 12.

Formula: Thickness (inches) ÷ 12 = Thickness (feet)

Example: 4 inches ÷ 12 = 0.333 feet

Step 4: Calculate Cubic Feet

Multiply your square footage by thickness in feet.

Formula: Square Footage × Thickness (ft) = Cubic Feet

Example: 192 sq ft × 0.333 ft = 64 cubic feet

Step 5: Convert to Cubic Yards

Divide cubic feet by 27 (since there are 27 cubic feet in a cubic yard).

Formula: Cubic Feet ÷ 27 = Cubic Yards

Example: 64 cubic feet ÷ 27 = 2.37 cubic yards

Step 6: Add Waste Factor

Here’s where experience comes in. I always add 10% for waste on smaller residential jobs. This accounts for:

Spillage during the pour
Slight variations in ground level
Over-excavation in spots
The concrete that stays in the truck

Formula: Cubic Yards × 1.10 = Total to Order

Example: 2.37 yards × 1.10 = 2.6 cubic yards

For a 12×16 patio at 4 inches thick, I’d order 2.6 to 3 yards of concrete.

Pro Tip: Ready-mix companies often have minimum delivery charges. If you’re close to a breakpoint (like 2.5 yards), it might cost the same to order 3 yards—and you’ll have the peace of mind.

Calculating Concrete for an L-Shaped Patio

L-shaped patios are common when extending from a back door along two walls. Here’s my approach:

Break It Into Rectangles

The easiest method is dividing the L into two rectangles, calculating each separately, then adding them together.

Example: An L-shaped patio with:

Section A: 12 ft × 10 ft
Section B: 8 ft × 6 ft

Section A Calculation:

Square footage: 12 × 10 = 120 sq ft
Cubic feet: 120 × 0.333 = 40 cubic feet
Cubic yards: 40 ÷ 27 = 1.48 yards

Section B Calculation:

Square footage: 8 × 6 = 48 sq ft
Cubic feet: 48 × 0.333 = 16 cubic feet
Cubic yards: 16 ÷ 27 = 0.59 yards

Total: 1.48 + 0.59 = 2.07 cubic yards

With 10% waste: 2.07 × 1.10 = 2.3 yards (I’d order 2.5 yards)

Watch Out: Make sure you don’t double-count any overlap when measuring your sections. I sketch it out on paper to avoid this mistake.

Calculating Concrete for Curved or Circular Patios

Curved patios look beautiful but require different math. Here are the two most common scenarios:

Full Circle Patio

Use the circle area formula you learned in school (πr²).

Formula: 3.14 × (Radius in feet)² × Thickness (ft) ÷ 27 = Cubic Yards

Example: A circular patio with a 10-foot diameter (5-foot radius):

Area: 3.14 × (5 × 5) = 78.5 sq ft
Cubic feet: 78.5 × 0.333 = 26.14 cubic feet
Cubic yards: 26.14 ÷ 27 = 0.97 yards
With waste: 0.97 × 1.10 = 1.07 yards (order 1.5 yards minimum)

Curved Edge Patio

For patios with one or more curved edges, I use one of two methods:

Approximate with rectangles: Divide the curve into smaller rectangular sections
Grid method: Lay out a 1-foot grid and count squares (tedious but accurate)
Digital tools: Use our concrete calculator which handles complex shapes

Honestly, for complex curves, I measure the area in sections and use digital tools to verify. It saves time and reduces errors.

The Quick Formula (For Those Who Hate Math)

If you just want a fast answer for a 4-inch thick rectangular patio:

Square Footage × 0.0123 = Cubic Yards

Then add 10% for waste.

Example: 200 sq ft patio

200 × 0.0123 = 2.46 cubic yards
Plus 10%: 2.46 × 1.10 = 2.7 yards

This formula only works for 4-inch thickness. For other depths, use the full calculation method above.

Ready-Mix Concrete vs. Bags: Which Should You Use?

This question comes up constantly. Here’s my honest take after two decades:

Use Ready-Mix When:

Area is over 100 square feet (roughly 1.2+ yards)
You want consistent quality
Time matters (mixing bags is SLOW)
You have truck access

Cost: $125-150 per cubic yard delivered (varies by region)

Use Bagged Concrete When:

Tiny projects (under 50 square feet)
No truck access (narrow side yard, backyard with no gate)
You need very small amounts

Cost: About $4-5 per 60-lb bag (covers ~0.45 cubic feet)

Example: A 2.5-yard job needs about 180 bags of 60-lb concrete. At $4.50 per bag, that’s $810 vs. $325-375 for ready-mix. Plus, you’ll spend an entire weekend mixing.

Pro Tip: I stopped using bags for anything over 1 yard about 15 years ago. The labor savings alone justifies ready-mix. If truck access is the issue, consider a concrete buggy or wheelbarrow relay with helpers.

Pro Tips From 20 Years of Concrete Work

Here’s the insider knowledge I’ve picked up over hundreds of pours:

1. Always Order 10% Extra (Minimum)

On larger jobs (6+ yards), I sometimes reduce this to 5-7%, but never less. The cost of running short far exceeds the cost of a small overage.

2. Sub-Base Thickness Affects Your Calculations

A proper patio needs 4-6 inches of compacted gravel base. If your sub-base isn’t level and compacted properly, you’ll end up with low spots that need extra concrete.

What I do: After excavating and installing the sub-base, I verify depth at multiple points before ordering concrete. I’ve saved myself from short orders many times this way.

3. When to Add Fiber Mesh

I add fiber mesh reinforcement (small plastic or steel fibers mixed into the concrete) for:

Large patios (over 200 sq ft)
Patios on unstable soil
Areas with freeze-thaw cycles

It costs about $5-7 extra per yard but dramatically reduces cracking. Add it when you order—it’s mixed at the plant.

Traditional wire mesh works too, but fibers are easier and distribute more evenly.

4. Sloping for Drainage

Patios should slope 1/4 inch per foot away from your house. This means one side will be slightly thicker.

Example: A 12-foot-wide patio needs a 3-inch drop from house to outer edge.

I usually ignore this in my concrete calculations if the slope is proper (it averages out). But if you’ve over-excavated or the slope is steeper, add 5-10% extra.

5. Check the Weather Forecast

Never pour concrete if:

Rain is forecast within 24 hours
Temperature will drop below 40°F within 48 hours
It’s above 90°F without proper curing plans

I’ve seen too many DIYers ignore this and end up with ruined slabs.

6. Have a Backup Plan for Extra Concrete

If you over-order, have a plan:

Small walkway section
Equipment pads
Stepping stones (use cardboard forms)

I keep some quick forms in my truck for exactly this reason.

Common Mistakes to Avoid

After watching countless pours (and making plenty of early mistakes myself), here are the errors I see most often:

Mistake #1: Measuring Width Instead of Length

Sounds silly, but it happens. Double-check your measurements, especially on complex shapes.

Mistake #2: Forgetting to Convert Inches to Feet

If you use 4 inches instead of 0.333 feet in your calculation, you’ll order 12 times too much concrete. I’ve seen this happen.

Mistake #3: Not Accounting for Ground Irregularities

Even with a proper sub-base, you’ll have slight variations. The 10% waste factor covers this, but if your excavation is sloppy, increase it to 15%.

Mistake #4: Using Online Calculators Blindly

Calculators are great for verification (like our concrete calculator), but always understand the math yourself. I’ve caught calculator errors that would’ve cost me money.

Mistake #5: Ordering Too Late

Ready-mix plants book up, especially in spring and summer. Order at least 3-5 days ahead, and confirm the morning of your pour.

Example Calculation: Real-World Patio Project

Let me walk you through a recent job I quoted:

Project: Backyard patio, 16 ft × 20 ft, 4 inches thick

Step 1 - Square Footage: 16 × 20 = 320 sq ft

Step 2 - Convert Thickness: 4 inches ÷ 12 = 0.333 ft

Step 3 - Cubic Feet: 320 × 0.333 = 106.56 cubic feet

Step 4 - Cubic Yards: 106.56 ÷ 27 = 3.95 cubic yards

Step 5 - Add 10% Waste: 3.95 × 1.10 = 4.34 cubic yards

What I Ordered: 4.5 cubic yards

What We Actually Used: 4.25 yards (had a small amount left over for a walkway patch)

Perfect execution. The 10% buffer saved us, and the extra quarter-yard filled a cracked section of existing sidewalk the homeowner wanted fixed.

Frequently Asked Questions

How much concrete do I need for a 10×10 patio?

For a standard 4-inch thick patio:

10 × 10 = 100 sq ft
100 × 0.333 = 33.3 cubic feet
33.3 ÷ 27 = 1.23 cubic yards
Plus 10% waste: 1.35 cubic yards

I’d order 1.5 yards to ensure you have enough.

Can I use a concrete patio calculator instead of doing the math?

Absolutely. Digital tools like the EstimationPro.AI concrete calculator are great for speed and accuracy, especially with complex shapes. I use them to verify my hand calculations on every job. But understanding the math yourself helps you catch errors and make field adjustments when needed.

How thick should a concrete patio be?

4 inches is the standard for residential patios with a properly compacted gravel base. Go thicker (5-6 inches) if you have poor soil, heavy furniture, or the patio will see vehicle traffic. Never go thinner than 3.5 inches for a patio.

How much does a yard of concrete cost?

As of 2025, ready-mix concrete costs $125-150 per cubic yard in most areas, including delivery. Prices vary by region, concrete strength (PSI), and additives (fiber mesh, accelerators, color). Small loads under 3 yards often have surcharges. Always get quotes from 2-3 local suppliers.

Should I include the sub-base in my concrete calculations?

No. Calculate concrete based on the slab thickness only (typically 4 inches). The sub-base is separate—usually 4-6 inches of compacted gravel installed before the pour. The sub-base supports the concrete but isn’t part of your concrete order.

Final Thoughts

Knowing how to calculate concrete for a patio is one of those skills that separates professionals from amateurs. Take your time with measurements, use the formulas I’ve outlined, add your waste factor, and verify with digital tools when needed.

Over my 20+ years in the business, accurate estimating has saved me thousands of dollars and countless headaches. Whether you’re pouring a simple 10×12 slab or a complex curved patio, the math is straightforward once you understand the steps.

Before you order, I recommend:

Measure twice (at minimum)
Calculate using the step-by-step method above
Verify with a concrete calculator
Add 10% for waste
Round up to the nearest quarter or half yard

And remember: it’s always better to have a wheelbarrow of concrete left over than to run short mid-pour.

Ready to calculate your patio? Use our free concrete calculator to get an instant estimate for your project, no matter the shape or size.

For a complete breakdown of what concrete patios cost including labor, base prep, rebar, and finish options, see our guide on concrete patio cost per square foot. And to check current ready-mix pricing in your area, use our Concrete Cost Per Yard calculator.

If you are comparing free calculators for your concrete work, our review of the best concrete calculators in 2026 tests and compares the top five options. For a broader look at concrete volume calculations covering slabs, footings, posts, and walls beyond just patios, the contractor guide on how much concrete do I need goes deep on every common pour type.

Brad is a licensed contractor with over 20 years of experience in residential and commercial concrete work. He’s the founder of EstimationPro.AI, helping contractors and DIYers estimate projects accurately.