Add rectangular slabs, cylinders, triangular pours, L-shapes, and circular rings in any combination. Get combined total volume and per-shape breakdown for your entire project.
Free to use
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No sign-up required
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5 shape types supported
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Imperial & metric supported
✓ Unlimited shapes per estimate✓ Per-shape volume breakdown✓ Cost estimator included✓ Last verified May 2026
Longest dimension of the pour area.Enter a valid length.
Shorter dimension of the pour area.Enter a valid width.
Slabs: 4–6 in typical. Footings: as designed.Enter a valid thickness.
Helps identify shapes in the breakdown.
⬭ Cylinder / Column / Post Hole
Sonotube/form diameter, or column width.Enter a valid diameter.
Post hole depth or column height.Enter a valid height.
Helps identify shapes in the breakdown.
△ Triangular Slab
The full width of the triangular base.Enter a valid base.
Perpendicular distance from base to apex.Enter a valid run.
Slab thickness.Enter a valid depth.
Helps identify shapes in the breakdown.
⌐ L-Shape — Two Rectangular Sections
Enter Section A and Section B separately. Both share the same depth. The calculator adds the two rectangles and avoids any overlap at the corner automatically (enter non-overlapping rectangles).
Enter a valid length.
Enter a valid width.
Enter a valid length.
Enter a valid width.
Same thickness applies to both sections.Enter a valid depth.
Helps identify shapes in the breakdown.
◎ Circular Ring — Hollow Cylinder
Outside edge of the concrete ring.Enter a valid outer diameter.
Diameter of the hollow center (pipe/void).Enter a valid inner diameter.
Depth of the ring or wall thickness height.Enter a valid height.
Helps identify shapes in the breakdown.
Add 10% for most pours. Add 15% for complex shapes or first-time pours.
$
Leave blank to skip cost estimate. US average: $100–$150/yd³.
Add multiple shapes, then click "Calculate Total" below to combine them.
Shapes Added (0)
Combines all shapes with your waste factor.
Combined Concrete Estimate
Total Concrete Volume (with waste)
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Cubic Yards (yd³)
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Cubic Feet (ft³)
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Cubic Meters (m³)
Per-Shape Breakdown (no waste)
#
Label / Shape
Dimensions
Net Volume (yd³)
Net Total (before waste)
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—Shapes
—Waste Factor
—Net yd³
—Waste Added (yd³)
Estimated Material Cost
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Concrete material cost only. Add labor, delivery, forming, and finishing for full project budget. Use our Full Project Estimator for a complete breakdown.
Final Volume = Net Total × (1 + waste% ÷ 100)
All dimensions converted to feet before calculation.
How to Use This Multi-Shape Concrete Calculator
Select the shape type and enter its dimensions.
Choose Rectangle, Cylinder, Triangular, L-Shape, or Circular Ring from the shape buttons. Enter measured dimensions in whatever unit is most convenient — the calculator converts everything internally. For cylinders, enter the form diameter (not radius) and depth. For L-shapes, break your slab into two non-overlapping rectangles and enter each section separately.
Click "Add This Shape to Estimate."
The shape appears in your running list with its individual volume. Repeat for every distinct shape in your project — a driveway with a curved apron, a deck with round footings, or a patio with an L-shaped pad and a separate rectangular walkway. Each shape is stored and can be removed individually if you make an error.
Set your waste factor and click "Calculate Total."
The default 10% waste factor is appropriate for most jobs. Increase to 15% for complex multi-shape pours where spillage and subgrade irregularities compound across shapes. Once all shapes are added, click the dark blue "Calculate Total" button to combine them and generate your final estimate.
Use the breakdown table to verify your order.
The per-shape breakdown shows net volume for each element — useful when ordering separate truck loads or when different shapes require different mix designs (e.g., structural columns at 4,500 PSI vs. a slab at 3,500 PSI). Give the cubic yards total to your ready-mix supplier or use the bag guidance to plan a bagged-concrete pour.
⚠ Pro Tip: When a project mixes shapes — like a slab with post holes for a deck — don't subtract the cylinder volumes from the slab. The post holes are in the ground, not in the slab. Add every distinct concrete pour as its own shape and let the calculator sum them. Mixing subtractions and additions is the most common calculation error on complex projects.
Multi-Shape Concrete Volume Formulas
Each shape uses its own geometric volume formula. All dimensions are converted to feet before calculation, then divided by 27 to convert cubic feet to cubic yards. The waste factor is applied once to the combined total — not per shape.
Shape
Formula (ft³)
Example
Result (yd³, no waste)
Rectangle / Slab
L × W × T
12 ft × 10 ft × 0.333 ft (4 in)
1.48 yd³
Cylinder / Column
π × r² × H
12 in dia × 48 in deep (r=0.5 ft, H=4 ft)
0.116 yd³
Triangular Slab
0.5 × Base × Run × Depth
10 ft × 8 ft × 0.333 ft
0.49 yd³
L-Shape
(L₁×W₁ + L₂×W₂) × T
(16×10 + 8×6) ft × 0.333 ft
2.67 yd³
Circular Ring
π × (R_outer² − R_inner²) × H
OD=48 in, ID=36 in, H=12 in
0.204 yd³
All examples use no waste factor. Add your waste factor to the final combined total before ordering.
Common Multi-Shape Project Reference Table
Pre-calculated totals for typical combined projects — 10% waste included.
Project Type
Shapes Included
Net yd³
With 10% Waste
Deck with 4 footings
Slab 16×12×4 in + 4× Cylinder 12 in dia × 48 in
3.03 yd³
3.33 yd³
L-shaped driveway + apron
L-shape (24×10 + 12×8)×6 in + Rect 12×10×6 in
8.67 yd³
9.53 yd³
Garage slab + 2 columns
Slab 24×24×6 in + 2× Cylinder 16 in dia × 96 in
11.34 yd³
12.47 yd³
Patio with triangular corner
Rect 20×14×4 in + Triangle base 8 ft run 6 ft × 4 in
4.46 yd³
4.91 yd³
Septic ring + slab lid
Ring OD 72 in ID 60 in H 18 in + Rect 7×7×4 in
1.10 yd³
1.21 yd³
8 post holes (standard deck)
8× Cylinder 10 in dia × 42 in deep
0.68 yd³
0.74 yd³
Walkway + landing pad
Rect 40×3×4 in + Rect 6×5×4 in
1.85 yd³
2.04 yd³
Volumes independently verified. Use as a sanity check for your own project, not as a substitute for calculating exact dimensions.
Which Shape Type Should I Use?
The most common error with multi-shape calculators is picking the wrong shape type for the pour. Use this guide to match your physical structure to the correct geometry.
Shape type selection guide — match your structure to the right formula.
Use only the perpendicular height, not the hypotenuse
L-shaped slab, U-shaped footing, wraparound pad
L-Shape
Both sections: length, width; shared depth
Do not overlap the sections — measure each arm separately
Manhole ring, pipe surround, hollow column
Circular Ring
Outer diameter, inner diameter (void), height
Inner diameter must be smaller than outer diameter
Irregular shape not covered above
Multiple rectangles
Break into rectangles, add each separately
For L, U, T shapes — break into non-overlapping rectangles
For cylindrical post holes, measure the sonotube's inside diameter — that's what gets filled with concrete. Sonotube labels show nominal outside diameter; the inside is typically 1/4 inch smaller. For an 8-inch tube, use 7.75 inches in the calculator for accuracy on large quantities.
Common Mistakes When Using a Multi-Shape Concrete Calculator
⚠️
Subtracting shapes that don't share the same pour.
A post hole sits in the ground, not inside a slab. A slab with columns through it is rare in residential work. Almost always, each concrete element should be added, not subtracted. If you find yourself trying to subtract a cylinder from a slab, stop and verify that the cylinder is actually a void in the slab plane itself — not a separate below-grade element.
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Using the hypotenuse instead of the perpendicular height for triangular pours.
The triangle formula uses base × perpendicular height, not base × slant length. If you measure the slant side of a right-triangle corner fillet, your volume will be too high by a factor of cos(θ). Always use the straight-across measurement from base to apex — the perpendicular run.
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Applying the waste factor once per shape instead of once to the total.
Waste factor applies to your ordering decision, not to each individual calculation. If you manually calculate each shape and add 10% to each one, then add them up, you haven't made a mathematical error — but your ordering will be correct only if the over-order is consistent. Apply the waste factor to the combined total, which is what this calculator does.
📏
Entering radius instead of diameter for cylinders and rings.
The calculator uses diameter as input — the full width of the tube or column, not the half-width. If you have a 6-inch sonotube, enter 6, not 3. A common mistake is to enter radius because "that's what's in the formula" — but this calculator already handles the r = diameter/2 conversion internally.
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Overlapping the sections of an L-shape.
When decomposing an L-shape into two rectangles, the sections must share no overlap. If your L-shape is 20×4 + 8×4 with the short arm extending off the long arm, define them so neither section covers the same square footage. If you include the corner in both rectangles, you'll overestimate volume.
Frequently Asked Questions
Calculate the volume of each shape separately using its geometric formula, convert all volumes to cubic yards, sum them to get your net total, then apply a single waste factor (typically 10%) to the combined total. This is exactly what this calculator does — add each shape one at a time and click Calculate Total when done. Never apply the waste factor per shape, as that distorts the proportional over-order.
Volume of a cylinder in cubic feet = π × (diameter ÷ 2)² × depth. Divide by 27 to get cubic yards. For example, an 8-inch diameter hole at 36 inches deep: radius = 4 in = 0.333 ft; depth = 3 ft; volume = 3.14159 × 0.333² × 3 = 1.047 ft³ = 0.039 yd³. For 10 such holes, you need about 0.39 yd³ net — roughly half a cubic yard with a 10% waste factor. Use the cylinder shape type in this calculator to skip the manual math.
Yes. Use the L-Shape type for L- or U-shaped slabs by entering two rectangular sections with the same depth. For a U-shape, decompose it into either two parallel arms (two rectangles), or one large rectangle minus a rectangular void — the latter requires you to calculate the void separately using Rectangle and subtract it from your total manually before entering. For most L-shapes, the two-rectangle approach is exact. For U-shapes, two parallel arm rectangles is typically easier.
Circular ring volume (ft³) = π × (R_outer² − R_inner²) × height, where R is radius in feet. For example, a manhole ring with a 48-inch outer diameter, 36-inch inner diameter, and 12-inch height: R_outer = 2 ft, R_inner = 1.5 ft; V = 3.14159 × (4 − 2.25) × 1 = 5.497 ft³ = 0.204 yd³. This shape appears in culvert collars, cistern walls, septic rings, pipe surrounds, and decorative circular garden features.
Only if different sections require different mix designs (different PSI, air entrainment, or fiber content) or if there's a time gap between pours that would create a cold joint. For most residential projects — a slab plus footings, or a walkway plus landing pad — pour everything in a single truck order. Ready-mix plants charge short-load fees for orders under 3–4 cubic yards, so combining shapes into one pour is almost always more economical than splitting into multiple deliveries.
An 80 lb bag yields 0.60 cubic feet of concrete. A standard 10-inch diameter hole at 36 inches deep is about 1.64 ft³, so you'd need 3 bags of 80 lb concrete per hole. A 12-inch hole at 48 inches deep is 3.77 ft³ — roughly 6–7 bags. Post holes for deck footings are typically sized to match the frost line depth in your region. For 8 or more holes, consider ready-mix if the volume totals over 1 cubic yard — it's faster and you'll get a more consistent mix.
Yes, by decomposition. Any polygon can be broken into a combination of rectangles and triangles. Add each piece as a separate shape in this calculator. For a hexagonal pad, divide it into 6 equilateral triangles. For a trapezoid, use one rectangle plus one or two right triangles. The more shapes you add, the more accurate your total. This technique is standard practice in estimating — surveyors and contractors use it on paper plans before CAD software became common.
Use 10% for straightforward multi-shape pours where each section is clearly defined and easy to form accurately. Increase to 12–15% when shapes are complex, forms are custom-built (rather than rented prefab), or when you're working with curved or irregular elements. Never go below 8% even on simple rectangular pours — subgrade is never perfectly flat and transit mixing results in small volume loss. For first-time pours or projects with multiple triangular or cylindrical shapes, 15% is not excessive.
This calculator does not automatically handle corner overlap — it's your responsibility to enter two non-overlapping rectangles. The standard approach: define Rectangle A as the full-length arm of the L (from end to end), then define Rectangle B as the perpendicular arm excluding the shared corner. For example, an L-shape that is 12 ft long × 4 ft wide with a 6 ft × 3 ft arm: enter Rect A as 12×4 and Rect B as 6×3 with the 3 ft not overlapping the 4 ft width. Sketch your L on paper and mark each section's boundaries before measuring.
