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Rectangular slab · Last reviewed 2026-07-12

Concrete slab and patio volume calculator

Use this mode when you already know a rectangular slab's length, width, and thickness. It keeps geometric volume separate from added waste and lets the same measured footprint start a gravel-base estimate.

SLAB OR PATIO

Slab or patio 1

Enter the rectangular slab measurements from your project plan.

Measurements

Length
Width
Thickness

Material quantities

No current result.

Complete every measurement with a valid value. Previous results stay hidden.

LINKED MATERIAL

Gravel base

Reuse this slab footprint without entering length or width again.

Formula and worked example

Area = length × width. Exact cubic feet = area × thickness in feet. Exact cubic yards = exact cubic feet ÷ 27. Waste volume is shown separately before the adjusted order quantity.

Example: 10 ft × 12 ft × 4 in gives 120 ft² and 40 ft³ (1.481481… yd³). At 10% waste, 4 ft³ is added for 44 ft³ (1.629629… yd³).

Assumptions, source, and limits

The concrete waste percentage is editable for this zone. Its linked gravel base reuses this footprint while keeping depth, compaction, waste, and density assumptions separate. Delivery, site preparation, drainage, tax, equipment, and labor are not modeled.

Source: Concrete Cal planning presets · Reviewed 2026-07-11.

Feet and inches are normalized once before the formula runs. The engine retains full precision and rounds only the displayed result.

Rectangular slab formula

Exact ft³ = length ft × width ft × (thickness in ÷ 12); order ft³ = exact ft³ × (1 + waste%)

Length times width gives square feet. Dividing thickness inches by 12 converts thickness to feet before it is multiplied by area. Divide cubic feet by 27 to show cubic yards.

Waste is a visible purchase allowance, not a structural safety factor. It never changes the exact geometric volume.

Worked example: 10 ft × 12 ft patio

For a 4 in slab, thickness is 4 ÷ 12 = 0.3333 ft. Area is 10 × 12 = 120 ft², so exact concrete is 120 × 0.3333 = 40.00 ft³, or 1.48 yd³.

At 10% waste, the allowance is 4.00 ft³ and the order volume is 44.00 ft³, or 1.63 yd³. This is normative Fixture A in the calculation specification.

Inputs and assumptions

Concrete waste starts at 10% and is editable. Thickness has no recommended default: enter the dimension from your own plan or project requirements.

Linked gravel stays off until you enable it. When enabled, it reuses only length and width; gravel depth and aggregate assumptions remain independent.

Reuse the measurement

After the slab result is valid, enable a linked gravel base to carry the same footprint into a separate compacted-depth calculation without typing length and width again.

Rectangular quantity boundary

This calculator does not model circular or irregular slabs, thickened edges, grade beams, slopes, or excavation variation.

It does not choose thickness, strength, reinforcement, joints, structural suitability, or code requirements.

Sources and review dates