Rebar Lap Splice Length Calculator

Plan safe splices with a practical, standards-inspired calculation approach for field use. Adjust for epoxy coating, top bars, and transverse reinforcement conditions with ease. Switch between units, bar sizes, and splice classes as needed. Review formulas used and stepwise guidance before exporting professional reports with confidence. Fast accurate results for your reinforcing design tasks.

Input Parameters
Conceptual presets set default factors/minimums; verify with actual code.
psi
Typical: 60,000 psi (US) or 420 MPa (SI)
psi
50% spliced at section
Enabled when Auto Class is off.
Result
Computed Lap Splice Length
Length (US)
— in
Length (SI)
— mm
Example Data
UnitsTypeBarfyf'cTopEpoxySpacingConf.ClassLightweightAction
UStension#5600004000nonogoodnormalAno
UStension#8600003000yesyespoornormalBno
SIcompression#650030nonogoodexcessAyes
Click “Load” to populate the form with a row's values.
Formula Used (standards-inspired approximation)

This tool implements a simplified, standards-inspired method resembling common practice. It is intended for preliminary sizing and education. Always verify with governing codes, project specifications, and a licensed engineer.

  1. Tension development length
    Approximate form:
    ld = (3 · ψt · ψe · ψs · fy) / (40 · λ · √f'c) · db
    Minimum check: ld ≥ 12 in (305 mm).
  2. Lap splice length in tension
    Ls,t = γclass · ld
    γclass = 1.0 (Class A) or 1.3 (Class B) in ACI preset.
  3. Compression lap splice (simplified)
    Ls,c = max(0.0009 · fy · db / (λ · √f'c), m·db)
    m depends on preset (e.g., 21 for ACI; see preset notes).
  4. Factors
    • ψt: 1.3 if top bar else 1.0 (ACI preset)
    • ψe: 1.2/1.5 when epoxy, else 1.0 (ACI preset)
    • ψs: 0.8 with excess transverse reinforcement else 1.0
    • λ: 0.75 for lightweight concrete, else 1.0

All lengths are reported in both inches and millimeters for convenience.

How to Use
  1. Select the unit system, code preset, splice type, and bar size.
  2. Enter strengths and choose conditions; enable Auto Class if desired.
  3. Press Calculate to compute the required lap splice length.
  4. Review governing factors then export to CSV or PDF.
US Bar Schedule (Informational)
BarDiameter (in)Diameter (mm)Area (in²)Weight (lb/ft)Action
#30.3759.50.110.376
#40.50012.70.200.668
#50.62515.90.311.043
#60.75019.10.441.502
#70.87522.20.602.044
#81.00025.40.792.670
#91.12828.71.003.400
#101.27032.31.274.303
#111.41035.81.565.313
Rounded informational values. Use mill certs and local standards for projects.
FAQs

A lap splice transfers force between adjacent bars by overlapping them sufficiently so that bond to concrete develops the required stress.

Class A typically applies when a smaller fraction of bars are spliced at a section; Class B is more conservative when a larger proportion is spliced. Confirm with detailing requirements.

Epoxy reduces bond, so factors increase development and splice lengths. The increase depends on cover and spacing conditions around the bar.

Minimums guard against variability in construction, bond conditions, and local stress concentrations, ensuring reliable force transfer under design actions.

Yes. “Top” bars cast with more than 12 in of concrete below tend to have higher required lengths because bleed water can reduce bond near the top surface.

No. Use this as a quick study tool. Always verify with the governing building code edition and project specifications.

Dual reporting aids international collaboration and reduces errors when exchanging details across unit systems.

Related Calculators

Aluminum Weight CalculatorBoard and Batten CalculatorBrick CalculatorDecking CalculatorDIY Shed Cost CalculatorFire Glass CalculatorFraming CalculatorFrench Drain CalculatorGlass Weight CalculatorGravel Calculator

Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.