Concrete
How to Calculate Concrete Yardage
Learn exactly how to calculate cubic yards of concrete for any slab, footing, or pour. Includes the formula, worked examples, and a link to our free calculator.
The Concrete Yardage Formula
Concrete yardage is a volume calculation. The formula is length in feet multiplied by width in feet multiplied by depth in feet, then divided by 27. The division by 27 matters because one cubic yard contains 27 cubic feet. Most mistakes happen at the depth step because slabs are usually described in inches. A 4 inch slab is 4 divided by 12, or 0.333 feet. Once all three dimensions are in feet, the formula is straightforward. This works for slabs, pads, footings, sidewalks, and many rectangular pours. For irregular shapes, break the project into simple rectangles, calculate each one separately, and add the cubic yards together.
Worked Example: 20ft x 10ft x 4in
A 20 foot by 10 foot slab that is 4 inches thick starts with the depth conversion. Four inches divided by 12 equals 0.333 feet. Multiply 20 by 10 by 0.333 and the slab contains about 66.7 cubic feet of concrete. Divide 66.7 by 27 and the slab needs about 2.47 cubic yards before waste. If you add a 10% waste buffer, the order becomes about 2.72 cubic yards. In the real world, most contractors would round this to a practical order amount based on the ready-mix supplier minimum and the confidence they have in the forms and subgrade.
Why Concrete Is Ordered in Cubic Yards
Ready-mix concrete is batched and delivered by volume, and cubic yards are the standard trade unit in the United States. A cubic yard is easier to use for truck delivery than cubic feet because slabs and footings quickly become large numbers in cubic feet. For example, a modest patio can be 80 cubic feet, but that is only 2.96 cubic yards. Suppliers, batch plants, and delivery tickets are built around yardage. Bagged concrete is different because each bag lists yield in cubic feet. That is why a good estimate should show both cubic yards and cubic feet, especially when you are deciding between ready-mix delivery and bags.
Bags vs Ready-Mix Delivery
Small repairs, fence posts, and very small pads can be handled with bagged concrete. Larger slabs are usually better suited to ready-mix because mixing dozens of bags is slow and physically demanding. As a rough rule, projects under one cubic yard may be reasonable with bags if labor is available. Projects over one cubic yard often deserve a ready-mix quote. A truck can place material faster, the mix is consistent, and the crew can focus on screeding and finishing instead of feeding a mixer. Cost still varies by region, short-load fees, delivery access, and minimum order size, so compare both options before committing.
Check the Estimate Before Ordering
Measure the inside of the forms, check the depth in several spots, and add waste before ordering. Concrete is unforgiving when a pour runs short. A cold joint from a late second batch can weaken the slab and leave a visible line. Extra concrete costs money, but being short costs more in labor, finish quality, and schedule risk. Use the SpecMath Concrete Slab Calculator to check your estimate instantly before ordering material.
Use the Concrete Calculator
Use our Concrete Slab Calculator to check your estimate instantly.
FAQ
What is the formula for calculating concrete yardage?
The formula is length in feet multiplied by width in feet multiplied by depth in feet, divided by 27. The depth must be converted from inches to feet before multiplying. Use the SpecMath Concrete Slab Calculator to confirm the yardage for your exact dimensions.
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27 to convert to cubic yards. One cubic yard equals 27 cubic feet because it is 3 feet by 3 feet by 3 feet. This conversion is built into the SpecMath calculator.
How many cubic yards does a concrete truck hold?
Many ready-mix trucks hold about 8 to 10 cubic yards of concrete. Smaller loads may be available, but short-load fees can apply. Ask the local supplier about minimums before ordering.