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Concrete Calculator

Professional-grade concrete estimator. Calculate volume, bag counts, rebar requirements, and costs for slabs, footings, columns, and stairs. Includes 25+ mix presets.

User Rating 0.0 ★★★★★
Total Usage 1 times
Category Foundation & Concrete
10%
Total Volume Required 0.00 yd³ 0.00 ft³
Est. Weight 0 lbs

Material BOM (Bill of Materials)

80lb Bags
0
Est. $0
60lb Bags
0
Est. $0
Ready-Mix Truck
0.0
Cubic Yards
Est. $0
#
Reinforcement Estimate

Based on standard grid spacing for selected projects.

0 ft
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About

Precision in concrete estimation is the difference between a profitable job and a logistical nightmare. This tool is designed for contractors and homeowners who need to account for every variable: from variable subgrade depths to specific aggregate densities.

Unlike basic calculators, this engine considers the compressive strength (psi) of different mixes, automatically estimates rebar reinforcement based on project type, and aggregates multiple shapes - allowing you to calculate a driveway, sidewalk, and porch footings in a single bill of materials.

We utilize the standard industry density of 145 lb/ft³ as a baseline but offer a database of 25+ specific mix types (including lightweight and high-strength) to ensure your bag count is accurate to the decimal.

concrete cement rebar foundation slab estimator construction cost

Formulas

Total volume Vtotal incorporates the Waste Factor W (typically 0.05 to 0.10) to account for spillage and uneven subgrades.

Vtotal = (n∑i=1 vi) × (1 + W)

Cylinder / Column Volume: Used for Sonotubes and post holes.

vcyl = π × (d2)2 × h

Bag Requirement: Calculated by dividing total weight by bag weight, rounded up.

Bags = ceil( Vft³ × DensityWeightbag )

Reference Data

Concrete ApplicationTypical PSIThickness (t)Rebar / Mesh Std.Density (lb/ft³)
Residential Driveway3000 - 40005 in#4 @ 18in OC145
Commercial Sidewalk40004 in#3 @ 24in OC145
Heavy Equip. Pad5000+8 - 12 inDouble Mat #5150
Countertop (GFRC)6000+1.5 inFiber Mesh135
Fence Post Setting2500N/ANone142
Lightweight Deck30003 inMesh100 - 115
Foundation Footing350012+ in#4 Continuous145
Hot Tub Slab45006 in#4 @ 12in OC145

Frequently Asked Questions

For a standard rectangular slab on a well-prepared base, 5% is sufficient. If excavating into uneven dirt, pouring deep footings, or using a pump truck (which leaves material in the hose), increase this to 10%. Complex shapes with many curves may require 15%.
The tool assumes a standard grid pattern (e.g., 18 inches on center) based on the project type selected. It calculates total linear feet of bar required, adding a 10% overlap margin for tying bars together.
Yes. Select "Stairs / Steps" from the shape menu. You will need to input the Rise (height), Run (depth), and Width of the stairs, along with the number of steps. The calculator includes the volume for the solid mass beneath the steps.
It is not just weight. The yield (volume produced) depends on the mix density. An 80lb bag of standard concrete yields approximately 0.60 cubic feet, while an 80lb bag of sand-mix might yield less. This tool adjusts based on the specific "Mix Type" density you select.
The tipping point is usually around 1.5 to 2.0 Cubic Yards. Mixing 90+ bags of 80lbs each is physically exhausting and time-consuming, risking a "cold joint" (where the first batch hardens before the last is poured). If the calculator shows > 1.5 CY, a truck is often the better choice despite short-load fees.