Slab-on-grade thickness reference
Pick a use and see the typical slab-on-grade thickness and reinforcement contractors plan around — labeled planning values, not a structural or geotechnical design.
Calculator
For a Residential slab / patio / sidewalk, a slab-on-grade is typically 4" over a compacted sub-base. Labeled planning values — a licensed engineer sizes load-bearing concrete.
How thick should a slab-on-grade be? The honest answer is that a licensed engineer sizes load-bearing concrete for your soil, loads and climate — but there are widely-used planning typicals that tell you what a normal residential slab looks like before you talk to a pro. This reference lets you pick a use and shows the thickness and reinforcement contractors commonly plan around, so you can sanity-check a quote or budget a pour.
These are labeled industry planning values, not a structural or geotechnical design. They do not account for your soil bearing, frost depth, expansive clay, point loads or local code. Treat them as a starting point for a conversation with a professional, never as an engineered specification.
Formula
This is a lookup, not a calculation: choose a use and the tool returns the labeled thickness band and the typical reinforcement.
residential slab / patio / sidewalk → ~4"
garage / shed slab → ~4–5"
driveway / heavy load → ~5–6"
reinforcement (typical) → #3–#4 rebar or WWM @ 12–18" o.c.
Thicker slabs and closer reinforcement spacing go with heavier and more concentrated loads — but the specific build for a load-bearing slab is an engineering decision.
Worked example
Choosing Residential slab / patio / sidewalk returns a typical thickness of 4" with #3–#4 rebar or welded wire mesh at 12–18" on center over a compacted sub-base. Choosing Driveway / heavy load steps the typical thickness up to 5–6". These bands come straight from the site’s labeled reference data.
Thickness in context
Thickness interacts with the rest of the build. A well-compacted, uniform sub-base does more for a slab’s performance than an extra inch of concrete over poor prep — see the gravel / sub-base calculator to size the base and the rebar calculator for a linear-foot reinforcement quantity at your chosen spacing. Control joints, cut at roughly 24–36 times the slab thickness in feet, help cracks form where you want them.
Because the values here are planning typicals and stable conventions — not prices and not code — this page never goes out of date. But it also never replaces engineering: for a slab that carries a structure, vehicles, or heavy equipment, or on questionable soil, have a licensed engineer specify the thickness, reinforcement and footings, and confirm against your local building code. When you are ready to price the pour, the concrete slab cost and garage / shed slab cost tools take it from here.
Reference table
Labeled slab-on-grade thickness typicals (NOT a structural design):
| Use | Typical thickness |
|---|---|
| Residential slab / patio / sidewalk | 4" |
| Garage / shed slab | 4–5" |
| Driveway / heavy load | 5–6" |
Typical reinforcement: #3–#4 rebar or welded wire mesh at 12–18" on center. A licensed engineer sizes load-bearing concrete.