Control joint calculator
Concrete cracks. Control joints decide where. The spacing rule is straightforward — in feet, use 2 to 3 times the slab thickness in inches — and joint depth should be a quarter of the slab thickness so the slab has a defined plane to crack along.
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This calculator needs JavaScript. The reference table below covers the common cases.
| Thickness | Spacing | Cut depth |
|---|---|---|
| 4 in | 8–12 ft | 1 in |
| 5 in | 10–15 ft | 1.25 in |
| 6 in | 12–18 ft | 1.5 in |
| 8 in | 16–24 ft | 2 in |
The formula
spacing (ft) = 2–3 × thickness (in) · joint depth = thickness ÷ 4
Worked example
A 4 in slab: joints every 8 to 12 ft, cut 1 in deep. A 6 in slab: joints every 12 to 18 ft, cut 1.5 in deep.
Reference table
| Thickness | Spacing | Cut depth |
|---|---|---|
| 4 in | 8–12 ft | 1 in |
| 5 in | 10–15 ft | 1.25 in |
| 6 in | 12–18 ft | 1.5 in |
| 8 in | 16–24 ft | 2 in |
Assumptions
- Keep panels as square as possible. Long, narrow panels crack across the middle.
- Saw cutting is typically done within 6 to 18 hours of placement; earlier with a soft-cut saw.
- Joint spacing tightens for mixes with higher shrinkage or where the subgrade restrains movement.