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# Calculate Concrete Development Length to AS 3600:2018
> Calculate tension and compression development lengths for reinforcement to AS 3600:2018 (Amdt 2), with code references and modification factors.
AustraliaAS 3600:2018 (Amdt 2)
Calculate tension and compression development lengths for reinforcement to AS 3600:2018 (Amdt 2), with code references on every output. Handles hooked and straight bars, and applies the standard's modification factors automatically.
## Method & scope
| Property | Detail |
| ---------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | AS 3600:2018 (Amdt 2) |
| Regions | Australia & New Zealand |
| What it checks | Basic development length in tension (AS 3600:2018, Cl. 13.1.2.2), Refined development length in tension (AS 3600:2018, Cl. 13.1.2.3), Development length in compression (AS 3600:2018, Cl. 13.1.5.3) |
#### Calculation method
The Concrete Development Length calculator computes tension and compression development lengths for reinforcing bars to AS 3600:2018 (Amendment 2), Section 13. It calculates both basic development lengths and refined development lengths, accounting for bar geometry, transverse reinforcement, cover, and stress conditions.
##### Basic development length in tension (AS 3600:2018, Cl. 13.1.2.2)
The basic tensile development length L\_sy,tb is the minimum length required for a straight bar to develop yield strength, assuming minimum cover and transverse reinforcement:
**L\_sy,tb = k\_1 × k\_3 × f\_sy × d\_b / (k\_2 × sqrt(f'c))**
Where:
* **k\_1**, bar position factor (1.3 for top bars with more than 300mm concrete below, 1.0 otherwise)
* **k\_2**, concrete density modification factor
* **k\_3**, bar size factor: (132, d\_b) / 100
Yield strength is limited to f'c ≤ 65 MPa. Bundled bars in tension are not covered.
##### Refined development length in tension (AS 3600:2018, Cl. 13.1.2.3)
The refined development length L\_sy,t applies modification factors for transverse confinement and transverse compression:
**L\_sy,t = k\_rdl × L\_sy,tb**
Where k\_rdl combines factors k\_4 (transverse confinement using the weighted average effectiveness factor lambda) and k\_5 (transverse compression pressure factor). The transverse confinement factor lambda = (A\_tr × n\_f, 0.25 × d\_b) / d\_b accounts for the number and area of fitment legs.
For bars that do not need to reach yield, a refined development length for unyielding bars L\_st = max(sigma\_st / f\_sy × L\_sy,t, 12 × d\_b) is also reported.
##### Development length in compression (AS 3600:2018, Cl. 13.1.5.3)
Basic compression development length L\_sy,cb is the greater of:
* 0.22 × f\_sy × d\_b / sqrt(f'c)
* 0.0435 × f\_sy × d\_b
Refined compression length L\_sy,c applies factor k\_6 = 0.75. For unyielding bars, L\_sc uses the actual bar stress sigma\_s rather than yield.
##### Outputs
The calculator reports L\_sy,tb, L\_sy,t, L\_st, L\_sy,cb, L\_sy,c, and L\_sc. The maximum development length L\_s,max across all conditions is also shown. All factor values and governing AS 3600:2018 clause references appear in the output.
##### Assumptions
Reinforced concrete beam with yield strength limited to 65 MPa. Bundled bars are not used in tension. No multiplication factor for bends or standard hooks in compression is applied.
## How to use it
Open it from **Run calc** in the About this calculator panel above.
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
## Common questions
The calculator applies AS 3600:2018 incorporating Amendment 2 for development length calculations. It implements the provisions of AS 3600:2018 Section 13, Development and splices of reinforcement, including the basic development length formula and all applicable modification factors (k1 through k7).
Key inputs are concrete compressive strength (f'c), bar diameter and grade (N or L reinforcement), cover to the bar being developed, transverse reinforcement details (bar size and spacing), bar geometry (straight or standard hook), and application type (top bar, bottom bar, or compression). For hooked bars, the hook geometry and cover details are also required.
Outputs include the basic development length (Lsy.t or Lsy.c) and the final design development length after applying all applicable modification factors. For hooked bars, the development length to the back of the hook and the minimum embedment are also reported. All AS 3600:2018 clause references and factor values are shown in the output.
The calculator applies the AS 3600:2018 Section 13 modification factors: k1 (bar position, top bars with more than 300mm concrete below), k2 (concrete density), k3 (bar size and transverse reinforcement), k4 (transverse confinement pressure), and k5 (excess reinforcement). For compression bars, the equivalent compression factors are applied.
Development length is the basis for lap splice design per AS 3600:2018 Section 13.2.3. The design lap length is calculated as the development length multiplied by a factor for the proportion of bars spliced (1.0 for 50% or less spliced, 1.3 for more than 50%). Enter the development length from this calculator to determine the required lap length for your splice configuration.
## Next steps
Complete list of Calcs.com design calculators available for Australian and New Zealand projects (AS 3600, AS 4100, AS 1720, AS/NZS 1170, and related standards).
Design concrete pad footings to AS 3600:2018 (Amdt 2) with instant moment, shear and punching shear results.
Fix footings that fail development length checks: switch to plain concrete, adjust thickness, or develop the rebar.
Design rectangular and circular reinforced concrete columns to AS 3600:2018 (Amdt 2), with P-M interaction, biaxial bending, slenderness and shear.
