How Do I Figure Out Concrete Yardage

How Do I Figure Out Concrete Yardage?

You've got a project. It's easy to walk away thinking you'll just "grab a few bags" from the hardware store. Maybe it's pouring a new slab for your garage, building a planter box, or filling a small hole in your driveway. On top of that, you stand in the space, looking at it, and the first real question hits: how much concrete do I actually need? But here's what most people learn the hard way—buying too little means multiple trips and delays, while buying too much wastes money and creates excess you don't need.

The good news? Figuring out concrete yardage isn't rocket science. It's math, but simple math that anyone can do with a tape measure and a calculator.

What Is Concrete Yardage?

When we talk about "yardage," we're referring to cubic yards—the unit concrete suppliers use when they deliver bulk concrete. That said, one cubic yard equals 27 cubic feet (it's based on a cube that's 3 feet long, 3 feet wide, and 3 feet tall). Ready-mix concrete typically comes in quantities measured in cubic yards, whether you're ordering a full truckload or just a fraction of one.

If you're using pre-mixed bags from the store, you'll still need to calculate in cubic yards to figure out how many bags you need, since bag instructions often reference coverage in cubic feet or yards.

Why It Matters

Getting the right amount isn't just about convenience—it affects your budget, timeline, and whether your project succeeds. Order too little, and you're stuck waiting for delivery while your concrete sets. Order too much, and you've got leftover concrete that's difficult to dispose of properly. Concrete that sits too long can be unusable, and breaking up extra slabs to reuse the material is a headache most DIYers don't want.

On larger projects, even small miscalculations become expensive. A mistake of half a cubic yard might seem minor, but at $150-$200 per cubic yard, that's real money on the line.

How to Calculate Concrete Yardage

Step 1: Measure Your Area

Grab a tape measure (or a long string and a measuring tape if you're working with irregular shapes). You need three dimensions:

• Length: How long is the area?
• Width: How wide is it?
• Depth: How deep does the concrete need to be?

For circular areas, measure the diameter instead of length and width. For irregular shapes, break the space into rectangles and circles you can measure separately.

Step 2: Convert Everything to Feet

Your measurements probably aren't in feet—they're in feet and inches. Here's the conversion trick: take your inches and divide by 12.

To give you an idea, if your slab is 12 feet long, 8 feet wide, and 4 inches deep:

• Length: 12 feet
• Width: 8 feet
• Depth: 4 ÷ 12 = 0.33 feet

Step 3: Multiply for Cubic Feet

Multiply length × width × depth. This gives you the volume in cubic feet.

Using our example: 12 × 8 × 0.33 = 31.68 cubic feet

Step 4: Convert to Cubic Yards

Divide your cubic feet result by 27 to get cubic yards.

31.68 ÷ 27 = 1.17 cubic yards

The Quick Formula

Here it is all together:

(Length × Width × Depth in feet) ÷ 27 = Cubic Yards

Most people round up to the nearest quarter or half yard when ordering, since suppliers rarely deliver fractions smaller than that.

Special Cases and Calculations

Circular Areas

For circles, use this formula:

π × radius² × depth ÷ 27

Where π is approximately 3.14. The radius is half the diameter.

Say you're filling a circular hole that's 18 inches across (9 inches radius) and 24 inches deep:

• Radius in feet: 9 ÷ 12 = 0.75 feet
• Depth in feet: 24 ÷ 12 = 2 feet
• Calculation: 3.14 × 0.75² × 2 ÷ 27 = 0.

Irregular Shapes

Break complex areas into simpler shapes. Calculate each one separately, then add them together.

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For an L-shaped patio base, measure the long rectangle and the short rectangle separately, calculate each volume, then sum them up.

Sloped or Contoured Areas

If you're filling a sloped area, measure the depth at several points along the length. Use the average depth for your calculation. For significant slopes, you might need to estimate more carefully or consult with your concrete supplier.

What Most People Get Wrong

Forgetting About Air Voids

When concrete is delivered, it's mixed with water and often includes air-entraining agents. The actual volume you place will be slightly less than what's ordered due to air pockets. Most suppliers build this into their pricing, but if you're calculating for bags, consider adding 5-10% extra.

Not Accounting for Waste

Spillage happens. On the flip side, formwork shifts. Worth adding: measurements get rounded. Industry practice is to add 10-15% to your calculated amount for typical projects. For precision work like garage slabs, you might need less. For messy jobs with lots of corners, add more.

Confusing Depth with Thickness

I see this mistake often with DIYers. They measure from the top of the form to the finished surface grade, forgetting that the concrete needs to extend below grade in some areas. Check your local building codes—basement footings and driveways often need specific thicknesses below the surface.

Mixing Up 80-Pound Bags with 60-Pound Bags

Different bag sizes cover different amounts. An 80-pound bag typically makes about 0.6 cubic feet (0.Because of that, 022 cubic yards). A 60-pound bag makes about 0.In practice, 45 cubic feet (0. Practically speaking, 017 cubic yards). Using the wrong conversion throws off your entire calculation.

Practical Tips That Actually Work

Always Round Up

Concrete suppliers won't deliver 0.Also, they work in 0. 17 cubic yards. On the flip side, 17 yards, order 1. If your math says you need 1.5. This leads to 25-yard increments minimum. It's cheaper to have a little extra than to make two trips.

Ask Your Supplier About Minimum Orders

Some suppliers have minimum order quantities (often 1-2 cubic yards). If your project is small, you might need to combine it with a neighbor's project or find a supplier with lower minimums.

Check Coverage Charts on Bag Packaging

Before you start measuring, flip over that bag of concrete mix. 6 cubic feet at 3 inches thick. For 80-pound Quikrete, one bag covers about 0.Which means it'll tell you exactly what size area a bag covers at various thicknesses. Use this as a cross-check to your calculations.

Use a Concrete Calculator App

There are dozens of reliable apps and online calculators that walk you through the process. But understand the math first—then use the tool to double-check your work.

Consider Delivered vs. Bagged Concrete

For anything over half a cubic yard, delivered concrete is usually cheaper per unit than bags. So you'll save on labor (mixing), time, and often money. But you need space to receive the pour and a way to move it from the truck to your forms.

Frequently Asked Questions

How many 80-pound bags equal a cubic yard?

One cubic yard equals 27 cubic feet. Since one 80-pound bag yields about 0.Which means 6 cubic feet, you need roughly 45 bags per cubic yard. That's a lot of bags to mix!

What if my measurements are in inches?

Convert everything to feet first. Divide inches by 12 to get feet. So 36 inches = 3 feet, 6 inches = 0.5 feet.

Can I just estimate?

For small projects, sure. Day to day, for anything involving a delivery or significant investment, double-check your math. A small error becomes expensive quickly.

What thickness should I use?

Check local building codes and manufacturer recommendations.