Free Concrete Volume Calculator with Overdig & Waste Factors

How It Works

1. Select Your Pour Shapes

   Choose from 8 shape types: rectangular slabs (with optional thickened edges), circular pads, triangles, footings, walls, columns, steps, or custom area. Add multiple shapes if your pour combines elements like a slab with thickened edges and column pads.

2. Enter Dimensions

   Input length, width, depth, diameter, or whatever the shape requires. The calculator shows an SVG preview with your dimensions labeled. Double-check depth units - entering 6 feet instead of 6 inches will order 12 times too much concrete.

3. Account for Overdig

   Is your subgrade at exact grade? If not, add average overdig depth (typically 0.5-2 inches). The calculator shows exactly how many extra cubic yards this adds. This is the step that separates a $200 mistake from a correct order.

4. Apply Waste Factor

   Waste happens on every pour. The calculator auto-selects waste factors by pour type: 7% for slabs, 12% for footings in dirt, 4% for formed walls. You can override, but it warns you if you go below safe minimums.

5. Review Your Order

   See total volume broken down by base, overdig, and waste. The calculator rounds UP to the next half-yard and gives you a final order number. This is the number you call into the ready-mix plant.

6. Check Delivery Details

   See truck capacity info, short load fee warnings if under 3-4 yards, and an estimated cost breakdown. Plan for extra concrete with practical suggestions.

Built For

• Contractors bidding slabs for garages, driveways, patios, and shop floors
• Concrete crews sizing pours for commercial foundations and footings
• DIY homeowners planning patio slabs, sidewalk sections, and carport pads
• Framers calculating footing volumes for decks, pergolas, and post-frame buildings
• Masons estimating concrete for retaining wall footings, column bases, and step pours
• Pool builders planning shell pours, equipment pads, and decking edges
• Agricultural builders sizing pads for equipment sheds, livestock shelters, and grain bins

Features & Capabilities

Overdig Allowance

The feature that separates this from basic calculators. Subgrade is never perfectly flat. Adding 0.5-1 inch average overdig can add 10-20% to your order. The calculator shows you exactly how much in cubic yards so there are no surprises on pour day.

Pour-Specific Waste Factors

Slabs on grade waste less (5-8%) than footings dug in dirt (10-15%). Formed walls waste even less (3-5%). Steps waste more (8-12%) due to complex screeding. The calculator auto-selects based on your shapes and explains the reasoning.

Multi-Shape Combining

Real pours aren't always simple rectangles. Combine a slab with thickened edges, add column pads, throw in a step section. The calculator sums all volumes and applies appropriate waste factors to the combined pour.

Short Load Fee Warning

Most ready-mix plants charge $30-50 per yard for orders under their minimum (typically 3-4 yards). The calculator flags this and shows the estimated fee so you can decide whether to combine pours or round up.

Thickened Edge Support

Garage slabs and building pads often have thickened perimeter edges that act as integral footings. Specify the edge width and extra depth to include this volume automatically instead of calculating it separately.

Visual Shape Previews

Each shape displays an SVG preview with your dimensions labeled. Helps you verify you entered the right numbers before committing to an expensive concrete order. Catches the classic "6 feet instead of 6 inches" mistake.

Comparison

Assumptions

• Volume calculated using standard geometric formulas with user-entered dimensions assumed accurate to the nearest inch
• Overdig allowance applied as uniform additional depth across the entire pour area
• Waste factors based on ACI field experience data: 5-8% for slabs, 10-15% for footings in earth, 3-5% for formed walls
• Concrete yield assumed at 27 cubic feet per cubic yard (standard ready-mix truck measure)
• Subgrade assumed reasonably compacted and graded — soft spots or uncompacted fill increase actual volume
• Thickened edge volumes calculated as trapezoidal cross-sections integrated along the perimeter length
• Final order rounded up to the nearest half-yard to account for measurement tolerance and minor site variations

Limitations

• Does not account for rebar or embedded items displacing concrete volume (negligible for most residential pours)
• Cannot verify subgrade conditions — actual overdig and soft spots may vary significantly from the entered estimate
• Does not calculate mix design, water-cement ratio, or specify concrete strength (PSI) for the order
• Irregular shapes must be approximated using available geometric primitives or the custom area input
• Does not estimate pump truck requirements, chute reach limitations, or site access logistics
• Sloped pours (driveways on grade, ramps) where thickness varies across the area require manual average depth estimation
• Does not account for concrete shrinkage, which reduces volume by approximately 0.5-1% after curing

References

• ACI 318 — Building Code Requirements for Structural Concrete (minimum thickness and reinforcement standards)
• ACI 332 — Residential Code Requirements for Structural Concrete
• ACI 304R — Guide for Measuring, Mixing, Transporting, and Placing Concrete
• Portland Cement Association (PCA) — Design and Control of Concrete Mixtures, 16th Edition
• ASTM C94 — Standard Specification for Ready-Mixed Concrete (batch tolerances and yield requirements)
• IRC Section R402 — Residential Concrete Foundation Requirements

Frequently Asked Questions