Quick Answer
For a 24×24 foot slab that is 4 inches thick, you will need approximately 6 cubic yards of concrete. The exact amount can be calculated by multiplying the length x width x thickness of the slab in feet, dividing by 27 to convert cubic feet to cubic yards. For a 24×24 slab that is 4 inches (0.33 ft) thick, the math is:
24 x 24 x 0.33 / 27 = 6 cubic yards
So for this size slab poured at 4 inches thick, plan for 6 yards of concrete to be delivered.
Calculating Concrete Needed for Slabs
When pouring concrete for a slab or foundation, it’s important to estimate the right amount so you don’t run short or end up paying for excess unused concrete. The quantity needed depends on the size and thickness of the slab.
Here are the steps for calculating cubic yards of concrete required:
1. Measure the length, width and thickness of the slab in feet. For example, a 24×24 foot slab that is 4 inches thick.
2. Multiply the length x width x thickness to calculate the volume in cubic feet.
24 x 24 x 0.33 (4 inches converted to feet) = 192 cubic feet
3. Divide the cubic feet result by 27 to convert to cubic yards.
192 cubic feet / 27 = 7.11 cubic yards
4. Round up to the nearest whole cubic yard.
For this example with a result of 7.11, round up to 8 cubic yards.
The formula is:
(Length x Width x Thickness) / 27 = cubic yards of concrete needed
So for any size slab, just input the dimensions in feet and calculate the cubic yards required. 4 inches of thickness is standard for many residential slabs like a patio, garage floor or shed foundation.
Concrete Thickness Guidelines
How thick should a concrete slab be? Here are some general guidelines on slab thickness by application:
– Residential garage slabs: 4 to 6 inches is typical
– Patios, sidewalks: 4 inches is standard
– Driveways: 4 to 6 inches
– Foundations: 6 to 8 inches
– Pole barn slabs: 5 to 7 inches
– Warehouse/commercial slabs: 5 to 7 inches
The thickness depends on the load requirements and what the concrete will be supporting. For light duty residential slabs like a patio or shed, 4 inches is usually adequate. For heavier loads like vehicles in a garage, driveways and commercial buildings, a thickness of 6 inches or more is recommended.
Factoring in Gravel Fill
When installing a concrete slab it’s important to also account for the gravel base that goes beneath the slab. 4 to 6 inches of gravel fill is typically compacted before the concrete is poured.
This gravel fill serves several purposes:
– Creates a stable base and prevents settling cracks
– Allows for drainage under the slab
– Acts as a moisture barrier to prevent groundwater rising up
The gravel layer should be included in the measurements when calculating concrete quantity. For example, with a 4 inch gravel base and 4 inch thick slab, the total depth for concrete calculations would be 8 inches.
Estimating for Waste
It’s always a good idea to add 5-10% extra to your concrete quantity estimate to allow for waste and overages in your actual pour. Having a yard or two extra is better than coming up short.
Some waste can occur from:
– Concrete sticking in the chute or pump during pouring
– Spills, splashes and overpour on the forms
– Testing samples taken from each batch
– Additional touch ups needed during finishing
By budgeting for 5% waste with an extra 1/2 yard included in your order, you can avoid headaches from running short on concrete for the job.
Ordering Concrete
When ordering concrete, you’ll need to specify key details so the ready mix supplier delivers the right amount:
– Quantity in cubic yards – Have your measurements and quantity calculated ahead of time
– Truck size – Order full truckloads when possible, may have minimums like 4-5 yards per truck
– Concrete mix – Strength rating like 3000 psi and any special mixes like fiber reinforced
– Delivery location – Provide clear directions and access for the concrete trucks
– Delivery date/time – Have your forms built and be ready for the pour to avoid delays
– Discharge time – Hourly rate may apply for lengthy pours requiring multiple trucks
Give as much notice as possible to the concrete company, ideally more than a few days ahead for planning. Promptly order add-ons if needed to avoid having too little concrete on site.
Pouring and Finishing the Slab
Once the gravel base is compacted and forms are constructed, you’ll want an experienced concrete contractor to handle the pour and finishing. Proper concrete pouring and finishing techniques are essential to achieve the desired smooth slab with the right pitch or slope. Consider hiring professionals for steps like:
– Setting up forms and reinforcement rebar grid as needed
– Delivering concrete trucks on site and directing unloading
– Spreading, screeding and consolidating the concrete to proper grade
– Floating and troweling for a smooth finish
– Applying control joints for crack control
– Adding desired decorative touches like stamped patterns, exposed aggregate etc
– Performing proper curing to gain strength
DIY is possible for basic slabs, but concrete finishing is tricky work best left to seasoned concrete contractors on larger jobs.
Community Feedback On Yardage Calculations
Getting community feedback from those who have poured concrete slabs can provide helpful insights on calculating and ordering concrete yardage. Here are some tips shared by experienced homeowners and contractors:
Watch Slab Dimensions
“Double and triple check your measurements – it’s easy to be off by a foot or two which can really throw off your concrete calculation. Measure twice to be sure, and add a couple extra inches on the thickness to be safe.”
Account for Rebar And Gravel
“Don’t forget to factor in gravel fill underneath and rebar mats inside the slab into your concrete quantity estimate. An extra few inches of depth makes a big difference in how much concrete you’ll need.”
Order an Extra Yard
“I always tell folks to order an extra yard of concrete even if their calculations seem perfect. It’s cheap insurance in case you need a bit more to finish the job, compared to having a half yard too little.”
Tool and Finishing Loss Add Up
“Between spillage, equipment waste, and touch ups during finishing, you can easily lose 200+ lbs of concrete per yard. Always budget 5-10% extra for finishing loss and miscellaneous waste.”
Don’t Screed Too Thin
“It’s tempting to spread the concrete thinner to make it go farther – don’t! Hold a minimum 4 inch thickness, screeding too thin risks cracking and weak spots down the road.”
Conclusion
Estimating concrete needs for slabs is an essential step before any pour. Be sure to carefully measure slab dimensions, account for fill layers and add extras to be safe. For a typical 24×24 foot residential slab at 4 inches thick, you’ll need approximately 6 yards of concrete delivered. Have your quantities dialed, and you’ll be sure to have just the right amount of concrete for a successful pour. Let our yardage estimate be a helpful starting point for your project!
