Fence Calculator
Setting fence posts in concrete? Estimate posts, rails, pickets, and concrete bags per post for your fence project.
Calculate Fence MaterialsConcrete Calculator
Work out exactly how much concrete you need for a slab, footing, column, or circular footing/cylinder. Pick a shape, enter your dimensions, and get an instant estimate in cubic feet, cubic yards, and cubic meters — with cubic yards front and center, since that's how ready-mix concrete is usually ordered.
Required Concrete
— cu yd
Concrete type—
Quantity—
Calculated volume (cu ft)—
Calculated volume (cu m)—
Waste allowance—
Required concrete (cu ft)—
Required concrete (cu m)—
How this calculator works
Every shape reduces to the same idea — figure out the volume of concrete needed, then add a waste allowance so you don't come up short partway through a pour.
Slab & footing — both are treated as a rectangular box:
Volume = Length × Width × Depth
Column — a rectangular post multiplied by its height:
Volume = Cross-section Length × Cross-section Width × Height
Circular footing / cylinder — uses the formula for the volume of a cylinder:
Volume = π × (Diameter ÷ 2)² × Depth
Whichever shape you choose, if you're calculating more than one (e.g. 6 footings or 4 columns), the volume is multiplied by the quantity you enter.
Waste allowance — extra material to cover spillage, uneven subgrade, and small measurement errors:
Required Concrete = Calculated Volume + (Calculated Volume × Waste % ÷ 100)
The final volume is then converted into cubic feet, cubic yards, and cubic meters. Cubic yards is shown as the headline result because that's the standard unit ready-mix concrete suppliers use for ordering in the US.
Example calculation — using this calculator's default slab values: a 10 ft × 10 ft slab, 4 inches deep, 1 slab, with a 10% waste allowance:
Depth = 4 in ÷ 12 = 0.333 ft
Volume = 10 × 10 × 0.333 × 1 = 33.33 cu ft
Waste Allowance = 33.33 × (10 ÷ 100) = 3.33 cu ft
Required Concrete = 33.33 + 3.33 = 36.67 cu ft ≈ 1.36 cu yd
With these inputs, you'd want to order about 1.36 cubic yards of ready-mix concrete — most suppliers will round this up to the nearest quarter yard when you place the order.
Factors That Affect Your Concrete Estimate
Depth accuracy
Depth has an outsized effect on volume since it's a direct multiplier. A small measurement error — or forgetting to switch the depth unit from inches to feet — can throw off your total significantly. Double-check the depth unit dropdown matches how you measured.
Waste percentage
10% is a reasonable default for a straightforward, well-formed pour. Uneven excavation, irregular shapes, or hand-mixing on site typically justify a higher percentage, since more material is lost to spillage and over-excavation.
Subgrade condition
An uneven or unexcavated subgrade means the actual poured depth often varies across the slab, using more concrete than a perfectly level calculation would suggest. Rough or sloped ground increases real-world usage.
Shape selection
Slabs and footings use the same rectangular-box formula, while columns and circular footings use different formulas. Make sure you've selected the shape that actually matches your project for an accurate volume.
Quantity
If you're pouring multiple identical footings, columns, or slabs, the quantity field multiplies your total directly — double-check this number, since it's an easy field to overlook or mistype.
Tips for a More Accurate Estimate
Round up to the nearest quarter yard
Ready-mix suppliers typically sell and deliver in quarter-yard increments and often charge a "short load" fee for small orders. Rounding your total up avoids a shortfall mid-pour and may help you avoid extra fees.
Double-check your depth unit
Slab and footing depth are commonly measured in inches while length and width are measured in feet — make sure the depth unit dropdown is set correctly before calculating, since this is the most common source of a large error.
Measure the actual excavated area
Where possible, measure the depth and dimensions of your excavation or formwork directly rather than relying solely on your project plans, since real-world digging rarely matches blueprints exactly.
Talk to your supplier about delivery minimums
Many ready-mix suppliers have minimum order sizes. If your calculated volume is small, ask about minimums and short-load fees in advance so there are no surprises on pour day.
Limitations of This Estimate
This calculator estimates raw concrete volume based on the dimensions you enter — it doesn't account for rebar, wire mesh, or other embedded materials, though their displacement is usually small enough to be covered by a normal waste allowance. It also assumes a uniform depth across the entire pour, while real subgrades are rarely perfectly level.
It doesn't include delivery fees, short-load charges, pump truck costs, or the price difference between various concrete mix strengths (PSI ratings) — those affect your budget but not the volume calculation itself. For structural pours (footings supporting a building, load-bearing columns, etc.), always confirm depth and volume requirements with a structural engineer or your local building code before ordering.
Frequently Asked Questions
Ready-mix concrete trucks in the US deliver and price concrete by the cubic yard, so it's the number you'll actually use when placing an order. Cubic feet and cubic meters are shown too for reference and for metric users.
10% is a typical starting point for most pours. Uneven or unexcavated ground, irregular shapes, and hand-mixing (versus truck delivery) can all justify a higher percentage — some contractors use 15–20% for tricky sites.
Mathematically they're calculated the same way (length × width × depth) — the distinction is just so you can label your project correctly and use realistic default dimensions for each.
Yes — most ready-mix suppliers sell in quarter-yard increments and charge a short-load fee for small orders, so it's common practice to round your final cubic yard figure up.
Select "Circular Footing / Cylinder" as the concrete type and enter the diameter and depth. The calculator uses the cylinder volume formula (π × radius² × depth) automatically — you don't need to calculate it by hand.
Standard residential slabs are commonly poured 4 inches deep, while driveways that need to support vehicle weight are often poured 5–6 inches deep. Check your local building code or a structural professional for load-bearing requirements.
No — rebar and wire mesh displace a small amount of concrete volume, but it's generally negligible and covered by a normal waste allowance. This calculator estimates raw concrete volume only.
Take the "Required concrete (cu ft)" result and check your specific bag's yield — most 80 lb bags yield about 0.6 cu ft, and most 60 lb bags yield about 0.45 cu ft. Divide your total cubic feet by the bag yield to get the number of bags.
Many ready-mix suppliers charge an extra fee for deliveries below a minimum volume (often around 3–5 cubic yards), since sending a full truck for a small order is inefficient. If your project is small, ask your supplier about this fee before ordering.
This calculator estimates one shape at a time. To get a combined total for a project with multiple shapes (e.g., footings plus a slab), calculate each shape separately and add the "Required concrete" results together before placing your order.
Depth is often measured in smaller units (inches or centimeters) than length and width, since slabs and footings are typically much thinner than they are wide. Selecting the correct depth unit ensures the calculator converts your measurement accurately.
It's accurate for planning purposes based on the dimensions and waste percentage you enter, but real pours can vary due to subgrade unevenness, formwork imperfections, and site conditions. For large or structural pours, confirm your final order with your concrete supplier or contractor.
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