Lap length calculator

Lap Length & Development Length Calculator

Compute L_d (development length) and tension/compression lap lengths. Formula: L_d = φ × 0.87 fy / (4 × t_bd)

Bar diameter φ (mm)

Yield stress fy (N/mm²)

Concrete grade (select for suggested t_bd) -- select -- M20 M25 M30 M35 M40

Bar type Deformed / RR bars (typical) Plain / smooth (rare for reinforcement)

Design bond stress t_bd (N/mm²) — override or use suggested

Suggested values are convenience presets — verify with IS/Project specs.

Development length L_d (mm)

Lap lengths (mm)

Tension lap (min) →

Compression lap (min) →

Step-by-step calculation

Thumb rules used: Tension lap = max(L_d, 30 × φ), Compression lap = max(L_d, 24 × φ). Always stagger laps to avoid weak sections.

If you have project/IS values for t_bd use those. Presets are only for quick checks.