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REBAR & STEEL · REBAR DEVELOPMENT LENGTH CALCULATOR

Development Length of #7 Rebar

A #7 bar (0.875 in) in 4,000 psi concrete with Grade 60 steel needs a tension development length of 41.5 in (47.4 bar diameters) by the ACI 318-19 simplified formula, for uncoated bottom bars with good spacing and cover. Top bars need 54.0 in, and a Class B tension lap is 54.0 in.

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Code & bar
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psi
psi
Development lengthDevelopment length 41.5 in41.5 insupport / concretemyconstructioncalculator.comNot to scale
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Results

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Development length in tension
41.5in
In bar diameters47.4 × db
Development length in compression16.6 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 ÷ (20·λ·√f'c) × db = 47.4 db = 1054 mm (41.5 in), min 12 in
  3. Compression: ldc = max(fy ÷ (50λ√f'c), 0.0003 fy) × db ≥ 8 in = 422 mm (16.6 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 ÷ (20 × λ × √f'c) × db     (No. 7 and larger, 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 #7 bar (db = 0.875 in), Grade 60, 4,000 psi normal-weight concrete, uncoated bottom bar:


    

  1. √4,000 = 63.25 psi
    2. 

  2. ld = 60,000 ÷ (20 × 63.25) × 0.875 = 41.5 in (47.4 db) → 12 in minimum does not govern
    3. 

  3. Top bar: × 1.3 = 54.0 in
    4. 

  4. Class B tension lap: 1.3 × 41.5 = 54.0 in
    5. 



Development Length of #7 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
47.9 in
62.3 in
62.3 in
19.2 in




4,000 psi
41.5 in
54.0 in
54.0 in
16.6 in




5,000 psi
37.1 in
48.3 in
48.3 in
15.8 in






More Development Lengths by Bar Size
Frequently Asked Questions
What is the development length of a #7 bar?
41.5 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 47.9 in, and in 5,000 psi it is 37.1 in.
How long is the development length of a #7 top bar?
54.0 in in 4,000 psi concrete, against 41.5 in for a bottom bar. Bars with more than 12 in of fresh concrete cast below them bond less well, because water and air rise under the bar, so ACI 318 multiplies their development length by ψt = 1.3.
How long is a Class B lap for a #7 bar?
54.0 in for a bottom bar in 4,000 psi concrete. Development length (41.5 in) is the embedment one bar needs to reach its full strength; a Class B tension lap, the usual case, joins two bars and is 1.3 × ld, at least 12 in.
Can a #7 bar be hooked instead of run straight?
Yes, where there is no room for 41.5 in of straight embedment. A bar ending in a standard 90° or 180° hook uses the hooked-bar development length ldh from ACI 318 §25.4.3, calculated separately and normally shorter than the straight length.
References
  • ACI 318-19 Table 25.4.2.3: ld = fy ψt ψe ψg ÷ (20 λ √f'c) × db for No. 7 and larger, 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