Concrete Pour Volume Calculator (Footing/Slab)
Calculate the concrete volume needed for a rectangular footing or slab pour. Enter the footing length in feet plus the width and depth in inches, and get the result in cubic yards.
Calculate Concrete Volume for Slab or Footing Pours
Concrete Pour Volume Formula
Where:
- \(Q\) — concrete volume required (yd³)
- \(D\) — length of the footing or slab run (ft), entered in the Diameter field
- \(W\) — width of the footing (in)
- \(H\) — depth or thickness of the pour (in)
- \(12\) — converts inches to feet
- \(27\) — converts cubic feet to cubic yards (1 yd³ = 27 ft³)
This formula computes the volume of a rectangular footing or slab strip: length × width × depth. The width and depth are converted from inches to feet before multiplying, and the total is divided by 27 to express the result in cubic yards, the standard unit for ordering ready-mix concrete.
Concrete Pour Volume – Calculation Example
Example: a deck footing trench runs 10 feet, with a width of 24 inches and a depth of 18 inches.
\[ W = \frac{24}{12} = 2 \text{ ft}, \quad H = \frac{18}{12} = 1.5 \text{ ft} \]
\[ Q = \frac{10 \cdot 2 \cdot 1.5}{27} = \frac{30}{27} \approx 1.11 \text{ yd}^3 \]
Result: about 1.11 cubic yards of concrete are needed for this pour. With a 10% waste allowance, order roughly 1.25 yd³.
How to use the calculator
- Enter the total length of the footing or slab run in feet in the Diameter field (e.g. 10).
- Enter the Width of the footing in inches (e.g. 24).
- Enter the Depth or thickness of the pour in inches (e.g. 18).
- Read the result under Footing pours, shown in cubic yards — the unit used by ready-mix suppliers.
What the calculator tells you
A footing is the concrete strip or pad that sits below a wall, deck post, or column and spreads the load onto the soil. A slab is the flat concrete surface used for floors, patios, and driveways. Both are poured as simple rectangular volumes, so the amount of concrete they need is the enclosed space: length times width times depth.
Ready-mix concrete in most markets is sold by the cubic yard, and suppliers typically have a minimum order (often around 1 yd³) plus delivery charges. Knowing your volume before you call lets you compare quotes, schedule a single delivery, and avoid paying for a short load fee or running short mid-pour — a cold joint between two batches is one of the weakest points a pour can have.
For the default values (10 ft × 24 in × 18 in), the result is 1.11 yd³. If you are mixing by hand or with a portable mixer, that is about 30 cubic feet of mixed concrete — a substantial job, which is why most footings of this size are ordered as ready-mix. For estimating bagged mix, one 80 lb bag yields roughly 0.6 ft³, so this pour would take about 50 bags.
If your footings are round pads or tubes rather than rectangular strips, the math changes: a circular footing uses \( \pi r^2 \) for the cross-section. The Concrete Column Fill calculator handles round shapes, and the Concrete Footing Volume calculator covers other footing configurations.
Assumptions, limitations and practical tips
- The pour is treated as a perfect rectangular prism. It assumes uniform width and depth along the whole run. Trenches dug slightly wide, uneven bottoms, or sloped sites will all take more concrete than calculated.
- Add a waste allowance of 5–10%. Spillage, over-excavation, and residue left in the truck or mixer all consume material. On the 1.11 yd³ example, ordering 1.25 yd³ is a safe margin.
- Units are fixed by the field labels. The length (Diameter field) must be in feet, while width and depth must be in inches. Mixing the units up is the most common source of error — a 24 entered as feet instead of inches would overestimate the pour by a factor of 12.
- This is volume only, not strength. The calculator does not check whether the footing size meets your local building code or soil conditions. For load-bearing footings, confirm dimensions with your engineer or code official.
- Each pour is calculated separately. For multiple footings of the same size, multiply the result by the number of pours, or run the calculator once with the combined total length.
For other project shapes, see the Concrete Yardage calculator for general slabs and pads, or the Concrete Slab Pour Volume calculator for slab-specific pours.
Frequently Asked Questions
How do I calculate concrete volume by hand for a footing or slab?
Multiply length × width × depth to get cubic feet, then divide by 27 to convert to cubic yards. Make sure all three dimensions are in feet first — divide any inch measurements by 12. For example, a 12 ft run that is 16 in wide and 8 in deep is \( 12 \times 1.33 \times 0.67 \approx 10.7 \) ft³, or about 0.40 yd³.
How many 80 lb bags of concrete equal one cubic yard?
One 80 lb bag of quikrete-style mix yields roughly 0.6 ft³ of concrete, so it takes about 45 bags per cubic yard. A 60 lb bag yields about 0.45 ft³, needing around 60 bags per yard. Bagged mix only makes sense for small pours — a full yard is a heavy, time-consuming job to mix by hand, and ready-mix is usually cheaper above roughly 1 yd³.
What size concrete footing do I need for a deck post or wall?
Footing size depends on the load, soil bearing capacity, and frost depth, which local building codes regulate. Common residential deck footings are 12–24 inches in diameter and extend below the frost line. This calculator only computes volume — it does not verify that your dimensions are adequate. Confirm footing sizes with your local code official or an engineer before pouring.
How do I convert the result to cubic feet or cubic meters?
Multiply cubic yards by 27 to get cubic feet, or by 0.7646 to get cubic meters. So the default result of 1.11 yd³ equals about 30 ft³ or 0.85 m³. Going the other way, divide cubic feet by 27 or cubic meters by 0.7646 to get back to cubic yards, the unit ready-mix suppliers quote.
How much extra concrete should I order beyond the calculated volume?
Add 5–10% for spillage, uneven trench bottoms, and residue left in the truck. On a calculated 1.11 yd³, that means ordering about 1.25 yd³. On sloped or rocky sites where the trench runs wide, lean toward 10%. Running short mid-pour is worse than a small leftover — a cold joint between two batches weakens the footing.
Why is my concrete estimate way too high or too low?
Almost always a unit mix-up. The length field must be in feet, while width and depth must be in inches. Entering 24 feet instead of 24 inches overestimates the pour by a factor of 12. Also check that you entered the total combined length for multiple footings, and that you didn't include the depth below grade twice if the trench is only partly filled.
How do I calculate concrete for multiple footings of the same size?
Run the calculator once for a single footing and multiply the result by the number of footings, or enter the combined total length of all runs at once — the math is identical. For example, eight footings each 2 ft long at 0.10 yd³ each total 0.80 yd³. For footings of different sizes, calculate each one separately and add the volumes.