Concrete Control Joint Spacing
Where to cut contraction (control) joints in a slab.
Example
You enter
- Slab thickness (in) 4
- Spacing factor (ft/in) 2.5
- Max spacing (ft) 18
- Slab length (ft, optional) 40
- Slab width (ft, optional) 24
You get
- Joint spacing 10.0 ft
- Saw-cut depth 1.00 in
- Panels 12
Checked against published worked examples from: NRMCA.
Details, formula, and sources
ScopeThe spacing in feet (about 2-3 times the slab thickness, capped), the saw-cut depth (a quarter of the slab), and the panel grid with an aspect-ratio check.
Formula or tableSpacing = min(factor x thickness, cap); depth = 0.25 x thickness; panels = ceil(length/spacing) x ceil(width/spacing); aspect kept under ~1.5:1.
Source and editionACI 302.1R / 360R slab-on-ground guidance (by name).
Free accessACI documents licensed; the rule of thumb is public practice.
What governsEstimate. AHJ and licensed professional govern.
API field namesslab_thickness_in, spacing_factor, max_spacing_ft, slab_length_ft, slab_width_ft, spacing_ft, depth_in, panels
- Spacing factor and cap ~2.5 ft per inch of thickness, capped ~15-18 ft (editable)ACI 302.1R / 360R