Reinforcement Overlap Calculator
Works with simple rules: length = base × bar diameter × factors. Choose unit system.
Units
Metric (mm)
US (in)
Lap type
Tension lap
Compression lap
Base rule
Simple: T=40d, C=30d
Tight tie: T=36d, C=24d
Poor tie: T=48d, C=36d
Custom base (enter below)
“d” is bar diameter
Bar diameter
mm (Metric) · in (US)
US rebar size (helper)
—
#3 (3/8 in)
#4 (1/2 in)
#5 (5/8 in)
#6 (3/4 in)
#7 (7/8 in)
#8 (1 in)
#9 (1.128 in)
#10 (1.27 in)
#11 (1.41 in)
Sets diameter for US units
Custom base for Tension (×d)
Custom base for Compression (×d)
Epoxy coated?
No
Yes (+20%)
Top bar?
No
Yes (+30%)
Top bar: more than ~300 mm / 12 in fresh cover
Tie / confinement
Good (×1.00)
Poor (+20%)
Seismic / high ductility
No
Yes (+20%)
Minimum lap length
Default used if empty
Round to
No rounding
Nearest 5 mm / 1/8 in
Nearest 10 mm / 1/4 in
Bar diameter d
Base × d
Total factor
Raw lap
Min lap rule
Final lap
This is a quick rule-of-thumb tool. Always follow your code and project specs.