The Locolory toolkit / Concrete & Masonry Estimator
Concrete Slab, Rebar & Material Estimator
Calculate cubic yards of concrete, premix bag counts, rebar grid requirements, and base aggregate tonnage for slabs, footings, and driveways.
Concrete Slab, Rebar & Material Estimator is a free browser-based utility that calculate cubic yards of concrete, premix bag counts, rebar grid requirements, and base aggregate tonnage for slabs, footings, and driveways.
- Core logic: calculate slab volume, bag equivalents, reinforcement grid lengths, and compacted base material from entered dimensions.
No software download, login, or server upload required. Computations execute locally on device.
Concrete material estimator
● Calculated locally
Waste margin
Example starting dimensions. Replace them with verified field measurements.
Material summary
Includes 10% wasteTotal concrete volume1.96 yd³1.50 cubic meters
Bag yields and aggregate density are planning assumptions. Rebar excludes laps, hooks, chairs, and dowels.
How to estimate concrete slab volume and bag counts accurately
For imperial measurements, use length × width × thickness in feet, then divide cubic feet by 27 for cubic yards. For a 4-inch slab, convert depth to 4 ÷ 12 feet first.
Bag counts divide total cubic feet by the manufacturer's stated yield—this estimate uses 0.60 ft³ for 80-lb bags and 0.45 ft³ for 60-lb bags. Unlike a saw cut list there is no kerf, but uneven subgrade, form movement, spillage, and handling create equivalent material loss. Apply a measured waste allowance.
Ordering and reinforcement notes
Ready-mix is usually ordered by cubic yard or cubic meter, while small placements may be practical with premix. Confirm minimum-load charges and whether the supplier rounds to quarter-yard increments.
Rebar output is a grid-length estimate, not a structural design or cutting schedule. Lap splices, hooks, chairs, openings, thickened edges, and dowels require additional material.
Planning reference
Concrete Thickness & Rebar Spacing Guide Table
General examples only—soil, loads, climate, code, and engineering govern the final design.
| Typical use | Common thickness | Example reinforcement |
|---|---|---|
| Walkway / patio | 4 in | #4 at 18–24 in |
| Passenger driveway | 5–6 in | #4 at 12–18 in |
| Heavy equipment pad | 6–8+ in | Engineered layout |
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Good questions. Clear answers.
How many 80-pound bags of concrete make one cubic yard?
An 80-pound premix bag typically yields about 0.60 cubic feet, so one cubic yard requires about 45 bags before waste. Product yields vary by mix and manufacturer; use the yield printed on the bag for purchasing.
How thick should a concrete patio or driveway slab be poured?
A residential patio or walkway is commonly 4 inches thick over a prepared base. Passenger-vehicle driveways are often 5–6 inches, while heavy vehicles or equipment pads may require 6–8 inches or an engineered design.
Why is a 10% waste buffer recommended when ordering ready-mix concrete?
Excavation and subgrade are rarely perfectly level, forms can bow, dimensions can vary, and a small amount remains in handling. A 10% allowance reduces the risk of a costly short load, though large, accurately formed pours may use a smaller verified margin.
What grid spacing should I use for rebar in a residential slab?
Number 4 rebar at 18–24 inches on center is a common planning range, but slab load, soil, thickness, joints, frost conditions, and local code can change the design. Structural reinforcement should follow the project drawings or an engineer's specification.