Slab Concrete Calculators
Written by Shakeel Alvi · Technically reviewed by Muhammad Qasim, PEC Reg. No. 63430 · Last reviewed: 2026-07-11
This is the largest category on the site — eight calculators — because a slab is the most common concrete pour there is, and the most common reason to need a different output than plain volume: cost, weight, or whether the thing can actually hold the load someone plans to put on it.
Slab Concrete Calculator
Estimate concrete for slabs, patios, and floors.
Concrete Pad Calculator (AC, Shed, Hot Tub, Generator)
Estimate concrete volume, bag counts, and cost for small equipment pads — AC unit, shed, hot tub, and generator presets included.
Monolithic Slab Concrete Calculator (Slab + Thickened-Edge Footing)
Calculate concrete volume for a monolithic slab — slab body plus integral perimeter footing in a single pour. Garage, house foundation, and shed presets with ACI 318 and IRC R403 compliance checks.
Concrete Slab Cost Calculator
Estimate cost of concrete for slabs, patios, and floors.
Concrete Slab Weight Calculator
Estimate weight of concrete for slabs, patios, and floors.
Concrete Slab Load Capacity Calculator
Estimate load capacity of concrete slabs.
Concrete Sidewalk Calculator
Estimate concrete volume, bags, and cost for slabs, patios, and floors.
Concrete Patio Calculator
Estimate concrete volume, bags, and cost for slabs, patios, and floors.
What you're deciding in this category
The first decision most people skip is which output they actually need. A driveway contractor wants cubic yards and a delivered price; an engineer checking an existing garage floor wants load capacity in PSF, a completely different calculation that doesn't touch volume at all. The second is thickness by use — a patio at 4 inches, a garage floor at 5 to 6, and specialty pads sized to what's sitting on them, an AC unit or a hot tub each with a manufacturer-specified footprint and load. The third is whether the slab stands alone or is monolithic with its own footing — a shed slab poured with a thickened perimeter edge in one continuous pour needs a different formula than a flat slab bearing on a separately poured foundation wall, and mixing the two up either double-orders the edge or leaves it thinner than code allows.
Which calculator fits which job
The eight tools split along three lines — general volume, a specialized shape or load case, and an output other than volume entirely; skim for whichever line matches the question you're actually asking.
- Slab Concrete Calculator
- The default entry point for any flat rectangular pour — length, width, and thickness in, cubic yards and bag counts out, with no preset shape or load case applied.
- Concrete Pad Calculator (AC, Shed, Hot Tub, Generator)
- Use this for a small equipment footprint — AC unit, shed, hot tub, generator — where the size is dictated by the equipment's own footprint rather than a room or yard dimension.
- Monolithic Slab Concrete Calculator (Slab + Thickened-Edge Footing)
- Use this when the slab and its perimeter footing pour together in one continuous placement — it adds the thickened-edge volume to the flat slab body instead of treating them as two separate orders.
- Concrete Slab Cost Calculator
- Same geometry as the general slab tool, but the output is a delivered price rather than a bag count — use it once you've settled dimensions and just need a number to compare against a contractor's quote.
- Concrete Slab Weight Calculator
- Use this for shipping, structural, or heavy-load planning where the number that matters is total weight in tons or pounds, not the volume that produced it.
- Concrete Slab Load Capacity Calculator
- An entirely different calculation from the other seven — it doesn't take a footprint at all, it takes thickness and PSI and returns how much distributed load the slab can bear, independent of the volume math elsewhere in this category.
- Concrete Sidewalk Calculator
- Use this for a long, narrow, continuous walkway where the input is a linear run and a fixed width rather than an open rectangular footprint.
- Concrete Patio Calculator
- Similar inputs to the sidewalk tool but built around irregular patio shapes and typical 4-inch residential thickness rather than a public-way width standard.
Standards that govern Slab Concrete
ACI 302.1R — The floor and slab construction guide governing jointing layout, finishing tolerance, and curing — the reason two slabs poured to the identical volume and thickness can perform completely differently depending on control-joint spacing and how the surface was finished.
ACI 318-19 — Sets the minimum thickness and reinforcement for a monolithic slab's integral footing edge — the load-bearing portion of a monolithic pour has to satisfy the same footing rules a separately poured foundation would, even though it's placed in one continuous run.
Treating the load-capacity tool as a check on the volume tool's thickness
It's a natural assumption that whatever thickness the volume calculator suggests must also be enough to carry whatever's parked or stacked on the slab, since both numbers come from the same category. They're not connected. Load capacity depends on compressive strength and subgrade support as much as thickness, and the load-capacity calculator needs those inputs entered separately — running the volume tool alone tells you how much concrete to order, not whether the finished slab will hold a loaded truck or a stack of pallets. Skipping that second calculation is how garages built for a sedan end up cracking under an RV.
Frequently Asked Questions
- How thick should my slab be?
- 4 inches for a patio or sidewalk, 5 to 6 for a garage floor or driveway-adjacent slab, and whatever a manufacturer specifies for an equipment pad — check the pad calculator's presets before defaulting to 4 inches for something heavier than foot traffic.
- What's the difference between the slab calculator and the load-capacity calculator?
- The slab calculator estimates how much concrete to order from a footprint and thickness. The load-capacity calculator is unrelated math — it takes thickness and PSI and returns how much distributed weight the finished slab can bear, and needs its own separate inputs.
- What makes a slab monolithic?
- The slab body and its perimeter footing are poured together in one continuous placement rather than as two separate pours — common on sheds and smaller garages where a full stem-wall foundation isn't required.
- Do I need reinforcement in a 4-inch slab?
- Wire mesh or rebar is strongly recommended even at 4 inches to control cracking, though the slab volume calculators here price concrete only — reinforcement is a separate estimate on the reinforcement hub.
- Why is subgrade prep mentioned so much on slab pages?
- Because a few inches of uneven grading changes the actual pour thickness far more than most people expect, and load capacity depends on subgrade support as much as the slab's own thickness and strength.