Cubic Feet to Yards of Concrete Calculator
Quickly convert concrete volume from cubic feet to cubic yards, estimate ordering quantity, and add a waste factor so you can plan slabs, footings, posts, walkways, and small pours with greater accuracy.
How to use a cubic feet to yards of concrete calculator
A cubic feet to yards of concrete calculator helps convert one of the most common jobsite measurements into the unit that ready-mix suppliers usually quote and deliver. Homeowners, contractors, masons, and remodelers often figure dimensions in feet because forms, tape measures, framing layouts, and site plans are commonly expressed that way. However, concrete is typically ordered in cubic yards. That mismatch is why this conversion matters. If you know your project needs a certain number of cubic feet of concrete, you need to divide by 27 to determine cubic yards.
The calculator above automates that process and also gives you the option to add a waste factor and round the order up for practical scheduling. On a real pour, exact math is only part of the story. Spillage, uneven subgrade, form bulges, overexcavation, and jobsite access issues can all affect the amount of concrete you actually need. Ordering slightly short can be expensive because a second trip or a small short-load delivery can add significant cost. Ordering too much is also wasteful. A good calculator helps you find the middle ground.
The core formula is simple:
For example, if your forms hold 81 cubic feet of concrete, the exact conversion is 81 ÷ 27 = 3 cubic yards. If you add a 10% waste factor, the adjusted amount becomes 3.30 cubic yards. Depending on the supplier and project type, you may then round up to 3.5 yards or another practical increment.
Why concrete is ordered in cubic yards
Concrete trucks and batch plants typically work in cubic yards because it is a practical large-volume unit for estimating, production, dispatch, and billing. A cubic yard equals 27 cubic feet, which is large enough to describe significant material volume without creating oversized numbers. For instance, saying a driveway takes 5.5 cubic yards is easier for dispatch and pricing than saying it needs 148.5 cubic feet. This standardization also helps when comparing quotes from suppliers and planning labor, placement time, and finishing operations.
For small projects, bagged concrete may be more economical or easier to manage than ordering ready-mix. But even then, cubic yard conversions remain useful because they help you compare bag yields to total job volume. Once you know your required cubic yards, you can estimate how many bags would be needed if you choose a dry mix product instead of truck-delivered concrete.
Basic conversion steps
- Measure the total volume of the forms or holes in cubic feet.
- Divide the cubic feet by 27 to convert to cubic yards.
- Add a waste factor based on project complexity and site conditions.
- Round the result up to a practical ordering increment.
- Confirm minimum order requirements and delivery policies with your supplier.
Common concrete volume examples
Different project types create different estimating patterns. A slab usually starts with length × width × thickness, while post holes may involve cylinders or square holes repeated many times. Footings can be continuous linear forms, and retaining wall fills often include a mixture of rectangular and irregular sections. Because of that, many people first calculate the total volume in cubic feet, then use a cubic feet to yards calculator to convert the result into order-ready units.
| Project Example | Approximate Dimensions | Volume in Cubic Feet | Exact Cubic Yards |
|---|---|---|---|
| Small patio slab | 12 ft × 12 ft × 4 in thick | 48.0 ft³ | 1.78 yd³ |
| Single-car driveway panel | 10 ft × 20 ft × 4 in thick | 66.7 ft³ | 2.47 yd³ |
| Garage slab section | 20 ft × 20 ft × 4 in thick | 133.3 ft³ | 4.94 yd³ |
| Sidewalk run | 4 ft × 50 ft × 4 in thick | 66.7 ft³ | 2.47 yd³ |
| Fence posts, 12 holes | 12 holes at about 1.6 ft³ each | 19.2 ft³ | 0.71 yd³ |
These examples show how quickly cubic feet turn into more practical order quantities in yards. They also illustrate why a waste factor matters. A slab with clean forms and easy access may only need a small allowance. A set of irregular footings, however, can vary enough that adding 10% to 15% might be prudent.
Formula details for slabs, footings, and post holes
Rectangular slab formula
For a rectangular slab, first convert the thickness to feet. A 4-inch slab is 4 ÷ 12 = 0.333 feet thick. Then calculate:
Once you have cubic feet, divide by 27 to get cubic yards. For example, a 15 ft × 20 ft slab at 4 inches thick contains about 100 cubic feet, which equals about 3.70 cubic yards before adding waste.
Continuous footing formula
Footings are usually estimated by total length multiplied by width and depth. If a footing runs 40 feet long, is 2 feet wide, and 1 foot deep, the volume is 80 cubic feet. Divide 80 by 27 and you get 2.96 cubic yards. If the trench walls are rough or the excavation is slightly oversized, adding 10% can be very reasonable.
Post hole formula
Post holes are often estimated one hole at a time and then multiplied by the number of holes. For a cylindrical hole, use the formula for cylinder volume. In practical field estimation, many people use standard charts or a post-hole calculator, then sum the cubic feet. Once that total is known, this cubic feet to yards calculator makes the order conversion easy.
How much waste factor should you add?
There is no single perfect waste factor for every project. The right allowance depends on form quality, grading precision, reinforcement congestion, placement method, and whether you are pumping, chute-pouring, or moving concrete manually. The better your site prep and measurement accuracy, the lower your waste factor may be. On residential work, a 5% to 10% allowance is common. On irregular work, or when excavation dimensions are difficult to control, 10% to 15% may be safer.
- 0% to 5%: Best for highly controlled forms and very accurate dimensions.
- 5% to 10%: Common for slabs, sidewalks, and straightforward residential pours.
- 10% to 15%: Better for trenches, irregular footings, rough excavation, and difficult access.
When in doubt, discuss your estimate with the supplier. They may recommend a rounding convention based on truck sizes, dispatch policies, and the likelihood of underordering. Some suppliers can help validate your dimensions before you finalize delivery.
| Input Cubic Feet | Exact Cubic Yards | With 5% Waste | With 10% Waste | With 15% Waste |
|---|---|---|---|---|
| 27 ft³ | 1.00 yd³ | 1.05 yd³ | 1.10 yd³ | 1.15 yd³ |
| 54 ft³ | 2.00 yd³ | 2.10 yd³ | 2.20 yd³ | 2.30 yd³ |
| 81 ft³ | 3.00 yd³ | 3.15 yd³ | 3.30 yd³ | 3.45 yd³ |
| 108 ft³ | 4.00 yd³ | 4.20 yd³ | 4.40 yd³ | 4.60 yd³ |
| 135 ft³ | 5.00 yd³ | 5.25 yd³ | 5.50 yd³ | 5.75 yd³ |
Ready-mix concrete versus bagged concrete
Once you know the cubic yards required, the next question is often whether to order ready-mix or use bagged concrete. The answer depends mainly on total volume, site accessibility, labor costs, and timeline. Ready-mix is generally the better choice for larger pours because it saves labor, improves consistency, and reduces mixing time. Bagged concrete may make sense for small projects, repairs, deck footings, or locations where a truck cannot reach.
As a rule of thumb, very small projects under about 1 cubic yard can sometimes be handled with bagged concrete if labor is available and placement is manageable. Above that, ready-mix often becomes more efficient. Even if the material cost per unit appears similar, labor, cleanup, and quality control can heavily favor truck-delivered concrete.
Practical ordering tips
- Confirm whether the supplier has a minimum load requirement or short-load fee.
- Check if the quoted quantity is billed to the nearest quarter-yard or by exact metered volume.
- Ask about truck washout procedures and site access requirements.
- Plan labor and finishing tools before the truck arrives.
- Have reinforcement, base prep, and forms fully complete before delivery day.
Real-world measurement and construction references
Concrete estimating should always be paired with sound construction guidance. For dimensions, thickness requirements, and project details, refer to recognized building or engineering resources whenever possible. Helpful public references include the U.S. General Services Administration, which provides design and construction guidance at gsa.gov. For broader building research and structural guidance, universities such as Purdue provide engineering education materials at purdue.edu. You may also consult federal transportation and pavement resources from the U.S. Department of Transportation at fhwa.dot.gov for concrete pavement and infrastructure information.
These sources are not direct order calculators, but they are highly valuable for understanding thickness, placement standards, and the broader construction context. The more accurately you define the physical dimensions of your project, the more reliable your cubic feet to yards conversion will be.
Frequently asked questions
How many cubic feet are in one yard of concrete?
One cubic yard contains exactly 27 cubic feet. That is the standard conversion used in concrete estimating.
How do I convert cubic feet to cubic yards quickly?
Divide the cubic feet by 27. If you have 54 cubic feet, the answer is 2 cubic yards. If you have 13.5 cubic feet, the answer is 0.5 cubic yard.
Should I always round up my order?
In most cases, yes. Concrete shortages are usually more disruptive than having a small surplus. The right rounding amount depends on supplier practices and project complexity. Many people round to the nearest quarter-yard for practical ordering.
What if I measured in inches for slab thickness?
Convert inches to feet before calculating cubic feet. Divide the thickness in inches by 12. For example, 6 inches equals 0.5 feet, while 4 inches equals about 0.333 feet.
Can this calculator help with footings and post holes?
Yes. As long as you know the total volume in cubic feet, the calculator will convert that amount to cubic yards and can apply waste and rounding for ordering guidance.
Best practices for more accurate concrete estimates
To improve estimate accuracy, measure every dimension twice, pay close attention to thickness variations, and account for any grade changes. A slab rarely has perfect subgrade everywhere, and trenches may widen slightly in soft or loose soil. If your forms include curves, recesses, thickened edges, or integrated footings, split the project into smaller shapes, calculate each volume separately, and then combine them. This method is usually more accurate than trying to estimate the entire pour as one rough shape.
It is also wise to think through placement logistics. A difficult path from truck to forms can increase spillage and timing pressure. Pumping concrete can improve placement but may change job costs and setup needs. Hot weather, cold weather, and windy conditions can also affect finish timing and crew efficiency, although they do not change the pure volume math.
Finally, remember that this calculator is a planning tool. It is excellent for converting cubic feet into cubic yards and giving a realistic ordering estimate, but your final order should still reflect site conditions, supplier guidance, and your tolerance for waste versus shortage risk.
Bottom line
A cubic feet to yards of concrete calculator solves one of the most important concrete estimating tasks: converting field-measured volume into supplier-ready ordering units. Since 1 cubic yard equals 27 cubic feet, the basic math is easy, but jobsite conditions make planning more nuanced. By adding a waste factor and rounding appropriately, you can create a more dependable concrete order and reduce the chance of costly delays.
Use the calculator above whenever you have total cubic feet and need a practical concrete yardage estimate. Whether you are pouring a patio, driveway, footing, walkway, or set of post holes, converting correctly and ordering thoughtfully can save time, money, and frustration.