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Thickness chart

How thick to pour it

Residential flatwork, not a structural spec. When a wall, a truck, or a code official is involved, the drawing wins over this chart.

Last updated

  • 4in

    Sidewalk

    3,000–4,000 PSI

    Joints every 4 to 5 feet. Four inches on compacted gravel is the usual residential call.

    Use 4 in

  • 4in

    Patio

    4,000 PSI

    Four inches is the standard. Go to 5 if a pickup or a hot tub will sit on it.

    Use 4 in

  • 5in

    Driveway, cars

    4,000 PSI

    Four inches can live on an honest base. Five inches sleeps better under daily cars.

    Use 5 in

  • 6in

    Driveway, trucks & RVs

    4,000–4,500 PSI

    Six inches. The slab is only as good as the gravel under it. Don't pour 6 inches on mush.

    Use 6 in

  • 4in

    Garage slab

    4,000 PSI

    Four inches in the field. Thicken the edges to 8–12 inches where a wall bears.

    Use 4 in

  • 4in

    Shed pad

    3,500–4,000 PSI

    Small pads are often a bag job. Keep it square, keep it 4 inches, and don't forget the waste.

    Use 4 in

  • 6in

    Hot tub pad

    4,000 PSI

    Six inches with mesh or fiber. Water is heavy and it never moves.

    Use 6 in

  • 4in

    Basement floor

    3,500–4,000 PSI

    Four inches over a vapor barrier. This is a thickness note, not a waterproofing spec.

    Use 4 in

Not a slab

Footings are width times depth times the run, not a photo of a pad. Use the footing calculator for those. A thickened edge under a garage wall is not the same as the 4-inch field. Don’t trace those with the slab tool and call it a takeoff. And don’t pour any of this on loose fill. Thickness will not save a bad base.

Base under the slab

Most of these slabs sit on about 4 inches of compacted crushed stone, more for driveways or soft ground. The gravel base calculator tells you how many tons to order.

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