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.
4in
Use 4 inSidewalk
3,000–4,000 PSI
Joints every 4 to 5 feet. Four inches on compacted gravel is the usual residential call.
4in
Use 4 inPatio
4,000 PSI
Four inches is the standard. Go to 5 if a pickup or a hot tub will sit on it.
5in
Use 5 inDriveway, cars
4,000 PSI
Four inches can live on a honest base. Five inches sleeps better under daily cars.
6in
Use 6 inDriveway, 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.
4in
Use 4 inGarage slab
4,000 PSI
Four inches in the field. Thicken the edges to 8–12 inches where a wall bears.
4in
Use 4 inShed 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.
6in
Use 6 inHot tub pad
4,000 PSI
Six inches with mesh or fiber. Water is heavy and it never moves.
4in
Use 4 inBasement floor
3,500–4,000 PSI
Four inches over a vapor barrier. This is a thickness note, not a waterproofing spec.
Not a slab
Footings are width times depth times the run, not a photo of a pad. 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.