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REBAR & STEEL · REBAR DEVELOPMENT LENGTH CALCULATOR

Development Length of #4 Rebar

A #4 bar (0.5 in) in 4,000 psi concrete with Grade 60 steel needs a tension development length of 19.0 in (37.9 bar diameters) by the ACI 318-19 simplified formula, for uncoated bottom bars with good spacing and cover. Top bars need 24.7 in, and a Class B tension lap is 24.7 in.

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Code & bar
Materials & conditions
psi
psi
Development lengthDevelopment length 19.0 in19.0 insupport / concretemyconstructioncalculator.comNot to scale
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Results

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Development length in tension
19.0in
In bar diameters37.9 × db
Development length in compression9.5 in
Compression in bar diameters19.0 × db

Uses the simplified code equations. Your structural drawings and the engineer of record govern: they may specify longer laps, different splice classes, or seismic detailing.

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Working
  1. ψt = 1, ψe = 1, ψg = 1, λ = 1, √f'c = 63.2 psi (≤ 100)
  2. ld = fy·ψt·ψe·ψg ÷ (25·λ·√f'c) × db = 37.9 db = 482 mm (19.0 in), min 12 in
  3. Compression: ldc = max(fy ÷ (50λ√f'c), 0.0003 fy) × db ≥ 8 in = 241 mm (9.5 in)
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formula


ld  = fy × ψt × ψe × ψg ÷ (25 × λ × √f'c) × db     (No. 6 and smaller, good spacing and cover)
      at least 12 in
ψt  = 1.3 for top bars, 1.0 otherwise;   ψe = 1.0 uncoated
ψg  = 1.0 for Grade 60;   λ = 1.0 normal-weight concrete
Lap = 1.3 ld (Class B) or 1.0 ld (Class A), at least 12 in


Worked Example


A #4 bar (db = 0.5 in), Grade 60, 4,000 psi normal-weight concrete, uncoated bottom bar:


    

  1. √4,000 = 63.25 psi
    2. 

  2. ld = 60,000 ÷ (25 × 63.25) × 0.5 = 19.0 in (37.9 db) → 12 in minimum does not govern
    3. 

  3. Top bar: × 1.3 = 24.7 in
    4. 

  4. Class B tension lap: 1.3 × 19.0 = 24.7 in
    5. 



Development Length of #4 Rebar by Concrete Strength


Grade 60, uncoated, normal-weight concrete, good spacing and cover.






Concrete
ld, bottom bar
ld, top bar
Class B lap, bottom bar
ldc, compression






3,000 psi
21.9 in
28.5 in
28.5 in
11.0 in




4,000 psi
19.0 in
24.7 in
24.7 in
9.5 in




5,000 psi
17.0 in
22.1 in
22.1 in
9.0 in






More Development Lengths by Bar Size
Frequently Asked Questions
What is the development length of a #4 bar?
19.0 in for an uncoated bottom bar in 4,000 psi concrete with Grade 60 steel and good spacing and cover. In 3,000 psi concrete it is 21.9 in, and in 5,000 psi it is 17.0 in.
Why do top bars need a longer development length?
Bars with more than 12 in of fresh concrete cast below them bond less well, because water and air rise under the bar. ACI 318 multiplies their development length by ψt = 1.3.
What is the difference between development length and lap length?
Development length is the embedment one bar needs to reach its full strength. A tension lap joins two bars and is a multiple of it: Class A = 1.0 ld and Class B (the usual case) = 1.3 ld, at least 12 in.
Does a hook shorten the development length?
Usually, yes. A bar ending in a standard 90° or 180° hook uses the hooked-bar development length ldh, calculated separately by ACI 318 §25.4.3, which is normally shorter than the straight-bar length.
References
  • ACI 318-19 Table 25.4.2.3: ld = fy ψt ψe ψg ÷ (25 λ √f'c) × db for No. 6 and smaller, at least 12 in
  • ACI 318-19 §25.4.9: compression development length ldc, at least 8 in
  • ACI 318-19 §25.5.2: tension lap splices, Class A = 1.0 ld and Class B = 1.3 ld, at least 12 in