TryBuildCalcLap Length Calculator IS 456 lap splice length estimator
Calculate rebar development length and lap splice length per IS 456:2000.
🕒 Last updated: August 13, 2026
Bar & Material Details
For a 16 mm Fe415 bar in M20 concrete, the development length is 752.2 mm (47.0φ) and the lap length is 1,504.4 mm (94.0φ).
Development Length (Ld)
Length: 752.2 mm
As a multiple of diameter: 47.0 × φ
Design bond stress used: 1.920 N/mm²
Design stress in bar (0.87 × fy): 361.05 N/mm²
Lap (Splice) Length
Length: 1,504.4 mm
As a multiple of diameter: 94.0 × φ
Governed by 2×Ld or 30×diameter, whichever is greater.
| Force / Splice Type | Development Length | Lap Length |
|---|---|---|
| Flexural Tension (beams, slabs, footings) | 752.2 mm (47.0φ) | 752.2 mm (47.0φ) |
| Direct Tension (ties, hangers, tension members) | 752.2 mm (47.0φ) | 1,504.4 mm (94.0φ) |
| Compression (columns, piles) | 601.8 mm (37.6φ) | 601.8 mm (37.6φ) |
Assumptions Used
IS 456:2000, Clause 26.2.1 & 26.2.5.1 | Deformed (HYSD/TMT) bars — design bond stress increased 60% over plain bars, per Clause 26.2.1.1 (Table 26) | Design stress in bar = 0.87 × fy | Straight bar development assumed (no hook/bend anchorage credit)
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Development Length Calculator.
Lap (splice) length reference
This page focuses on lap (splice) length — pre-selected to direct tension, which needs roughly double the development length since neither spliced bar can rely on the other for confinement.
Edit the force/splice type, bar diameter, or grades above and the lap length, development length, and worked example all update from the active selections.
- Direct tension lap length = greater of 2 × Ld or 30 × diameter.
- Flexural tension lap length = greater of Ld or 30 × diameter.
- Compression lap length = greater of Ld (compression) or 24 × diameter.
How Is Development Length & Lap Length Calculated?
Per IS 456:2000, Clause 26.2.1 (development length) and Clause 26.2.5.1 (lap length).
Step 1 — Design Bond Stress (τbd)
Base τbd (plain bars, tension) — from Clause 26.2.1.1 (Table 26) by concrete grade
Deformed (HYSD/TMT) bar τbd = Base τbd × 1.6
Compression τbd = Tension τbd × 1.25
Design bond stress depends on the concrete grade and whether the bar is a plain or deformed (ribbed) bar — deformed bars get a 60% higher allowable bond stress since their ribs mechanically interlock with the surrounding concrete. Bars in compression get a further 25% increase, since a compressed bar bears directly against the concrete at its end in addition to bond along its length.
Step 2 — Development Length (Ld)
Design Stress in Bar (σs) = 0.87 × fy
Ld = (Diameter × σs) ÷ (4 × τbd)
This is the minimum straight embedment length beyond a critical section needed for the bar to safely reach its full design stress through bond with the surrounding concrete. As a sanity check, a Fe415 bar in M20 concrete under flexural tension works out to Ld ≈ 47 × diameter — a commonly cited reference figure.
Step 3 — Lap (Splice) Length
Flexural Tension: greater of Ld or 30 × Diameter
Direct Tension: greater of 2 × Ld or 30 × Diameter
Compression: greater of Ld (compression) or 24 × Diameter
The required overlap when splicing two bars end-to-end depends on how the bar is loaded — a direct-tension splice needs roughly double the development length since neither spliced bar can rely on the other for confinement, while a compression splice can be shorter since the bar also bears directly at its end.
Worked Example
This example walks through your current selections above, using the same steps as the Formula section.
Selections Used
| Selection | Value | Why it is used |
|---|---|---|
| Bar diameter | 16 mm | Ld and lap length both scale directly with diameter |
| Steel grade | Fe415 | Sets the design stress in the bar (0.87 × fy) |
| Concrete grade | M20 | Sets the base design bond stress from Clause 26.2.1.1 (Table 26) |
| Force / splice type | Direct Tension (ties, hangers, tension members) | Determines the τbd used (tension vs. compression) and the lap length formula |
Step 1 — Design Bond Stress
| Calculation | Result |
|---|---|
| Design bond stress used (τbd) | 1.920 N/mm² |
| Design stress in bar (σs = 0.87 × fy) | 361.05 N/mm² |
Step 2 & 3 — Development Length and Lap Length
| Force / Splice Type | Development Length | Lap Length |
|---|---|---|
| Flexural Tension (beams, slabs, footings) | 752.2 mm (47.0φ) | 752.2 mm (47.0φ) |
| Direct Tension (ties, hangers, tension members) | 752.2 mm (47.0φ) | 1,504.4 mm (94.0φ) |
| Compression (columns, piles) | 601.8 mm (37.6φ) | 601.8 mm (37.6φ) |
Therefore, a 16 mm Fe415 bar in M20 concrete needs a development length of 752.2 mm (47.0φ) and a lap length of 1,504.4 mm (94.0φ) for direct tension (ties, hangers, tension members).
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.