COCOMO Quick Reference

Comprehensive reference for the Constructive Cost Model (COCOMO) family of estimation models.

Basic COCOMO

Model Equations 

Effort (Person-Months) = a × (KLOC)^b
Duration (Months) = c × (Effort)^d
Team Size = Effort / Duration

Project Types and Constants

Project Mode a b c d Description
Organic 2.4 1.05 2.5 0.38 Small teams, familiar problem
Semi-detached 3.0 1.12 2.5 0.35 Medium teams, mixed experience
Embedded 3.6 1.20 2.5 0.32 Complex systems, tight constraints

Project Mode Selection Criteria

Organic Projects:

  • Team size: 2-8 people
  • Application domain: Familiar
  • Requirements: Stable and well-understood
  • Environment: Stable tools and methods
  • Examples: Business applications, data processing

Semi-detached Projects:

  • Team size: 8-30 people
  • Application domain: Mixed familiarity
  • Requirements: Mix of familiar and new
  • Environment: Some new tools/methods
  • Examples: Operating systems, DBMS, complex web apps

Embedded Projects:

  • Team size: Often > 30 people
  • Application domain: Unprecedented
  • Requirements: Complex, changing
  • Environment: Tight hardware/software constraints
  • Examples: Real-time systems, avionics, telecommunications

Intermediate COCOMO

Effort Multipliers

Product Attributes

| Attribute | Very Low | Low | Nominal | High | Very High | Extra High | |———–|———-|—–|———|——|———–|————| | RELY (Reliability) | 0.75 | 0.88 | 1.00 | 1.15 | 1.40 | - | | DATA (Database Size) | - | 0.94 | 1.00 | 1.08 | 1.16 | - | | CPLX (Complexity) | 0.70 | 0.85 | 1.00 | 1.15 | 1.30 | 1.65 |

Hardware Attributes

| Attribute | Very Low | Low | Nominal | High | Very High | Extra High | |———–|———-|—–|———|——|———–|————| | TIME (Execution Time) | - | - | 1.00 | 1.11 | 1.30 | 1.66 | | STOR (Main Storage) | - | - | 1.00 | 1.06 | 1.21 | 1.56 | | VIRT (Virtual Machine) | - | 0.87 | 1.00 | 1.15 | 1.30 | - | | TURN (Turnaround Time) | - | 0.87 | 1.00 | 1.07 | 1.15 | - |

Personnel Attributes

| Attribute | Very Low | Low | Nominal | High | Very High | |———–|———-|—–|———|——|———–| | ACAP (Analyst Capability) | 1.46 | 1.19 | 1.00 | 0.86 | 0.71 | | AEXP (Applications Experience) | 1.29 | 1.13 | 1.00 | 0.91 | 0.82 | | PCAP (Programmer Capability) | 1.42 | 1.17 | 1.00 | 0.86 | 0.70 | | VEXP (Virtual Machine Experience) | 1.21 | 1.10 | 1.00 | 0.90 | - | | LEXP (Language Experience) | 1.14 | 1.07 | 1.00 | 0.95 | - |

Project Attributes

| Attribute | Very Low | Low | Nominal | High | Very High | |———–|———-|—–|———|——|———–| | MODP (Modern Practices) | 1.24 | 1.10 | 1.00 | 0.91 | 0.82 | | TOOL (Software Tools) | 1.24 | 1.10 | 1.00 | 0.91 | 0.83 | | SCED (Schedule Constraint) | 1.23 | 1.08 | 1.00 | 1.04 | 1.10 |

COCOMO II

Scale Factors

Used to calculate the scale exponent: E = B + 0.01 × Σ(Scale Factors) where B = 0.91

Scale Factor Very Low Low Nominal High Very High
PREC (Precedentedness) 6.20 4.96 3.72 2.48 1.24
FLEX (Development Flexibility) 5.07 4.05 3.04 2.03 1.01
RESL (Architecture Risk Resolution) 7.07 5.65 4.24 2.83 1.41
TEAM (Team Cohesion) 5.48 4.38 3.29 2.19 1.10
PMAT (Process Maturity) 7.80 6.24 4.68 3.12 1.56

COCOMO II Equation 

Effort = A × (Size)^E × Π(EMi)
Duration = C × (Effort)^F

Where:

  • A = 2.94 (calibration constant)
  • Size = software size in KSLOC or unadjusted function points
  • E = scale exponent
  • EMi = effort multipliers
  • C = 3.67 (schedule constant)
  • F = D + 0.2 × (E - B) = D + 0.2 × (E - 0.91), where D = 0.28

Effort Multipliers (COCOMO II)

Product Factors

| Factor | Very Low | Low | Nominal | High | Very High | Extra High | |——–|———-|—–|———|——|———–|————| | RELY | 0.82 | 0.92 | 1.00 | 1.10 | 1.26 | - | | DATA | - | 0.90 | 1.00 | 1.14 | 1.28 | - | | CPLX | 0.73 | 0.87 | 1.00 | 1.17 | 1.34 | 1.74 | | RUSE | - | 0.95 | 1.00 | 1.07 | 1.15 | 1.24 | | DOCU | 0.81 | 0.91 | 1.00 | 1.11 | 1.23 | - |

Platform Factors

| Factor | Very Low | Low | Nominal | High | Very High | Extra High | |——–|———-|—–|———|——|———–|————| | TIME | - | - | 1.00 | 1.11 | 1.29 | 1.63 | | STOR | - | - | 1.00 | 1.05 | 1.17 | 1.46 | | PVOL | - | 0.87 | 1.00 | 1.15 | 1.30 | - |

Personnel Factors

| Factor | Very Low | Low | Nominal | High | Very High | |——–|———-|—–|———|——|———–| | ACAP | 1.42 | 1.19 | 1.00 | 0.85 | 0.71 | | PCAP | 1.34 | 1.15 | 1.00 | 0.88 | 0.76 | | PCON | 1.29 | 1.12 | 1.00 | 0.90 | 0.81 | | APEX | 1.22 | 1.10 | 1.00 | 0.88 | 0.81 | | PLEX | 1.19 | 1.09 | 1.00 | 0.91 | 0.85 | | LTEX | 1.20 | 1.09 | 1.00 | 0.91 | 0.84 |

Project Factors

| Factor | Very Low | Low | Nominal | High | Very High | |——–|———-|—–|———|——|———–| | TOOL | 1.17 | 1.09 | 1.00 | 0.90 | 0.78 | | SITE | 1.22 | 1.09 | 1.00 | 0.93 | 0.86 | | SCED | 1.43 | 1.14 | 1.00 | 1.00 | 1.00 |

Size Estimation Guidelines

Lines of Code (SLOC)

  • Physical LOC: Count actual lines in source files
  • Logical LOC: Count executable statements
  • Exclude: Comments, blank lines, data declarations
  • Include: Modified and reused code with effort multipliers

Function Points to SLOC Conversion

| Language | SLOC per FP | Range | |———-|————-|——-| | Assembly | 320 | 213-427 | | C | 128 | 85-171 | | COBOL | 106 | 71-141 | | Java | 53 | 35-71 | | C++ | 53 | 35-71 | | Visual Basic | 32 | 21-43 | | Python | 27 | 18-36 | | SQL | 12 | 8-16 |

Model Selection Guidelines

When to Use Basic COCOMO

  • Early project phases
  • Rough order-of-magnitude estimates
  • Limited project information available
  • Simple, straightforward projects

When to Use Intermediate COCOMO

  • Detailed estimates needed
  • Project characteristics well understood
  • Risk assessment required
  • Budget and schedule planning

When to Use COCOMO II

  • Modern development environments
  • Object-oriented or component-based development
  • Reuse considerations important
  • Process maturity variations

Common Applications

Project Planning

  1. Effort Estimation: Total person-months required
  2. Schedule Estimation: Project duration
  3. Team Sizing: Number of people needed
  4. Cost Estimation: Budget requirements

Risk Assessment

  1. Sensitivity Analysis: Impact of parameter changes
  2. Best/Worst Case: Range of possible outcomes
  3. Critical Factors: Most sensitive parameters
  4. Mitigation Planning: Address high-risk factors

Process Improvement

  1. Benchmark Current Performance: Compare to model predictions
  2. Identify Improvement Areas: Low-performing factors
  3. Track Progress: Monitor improvements over time
  4. Set Goals: Target productivity levels

Model Limitations

Assumptions

  • Stable requirements: Changes increase effort significantly
  • Competent management: Poor management can double effort
  • Reasonable budget and schedule: Extreme constraints reduce productivity
  • Lifecycle consistency: Single development approach throughout

Not Suitable For

  • Maintenance projects: Different effort patterns
  • Very small projects (< 2 KLOC): High overhead percentage
  • Non-procedural languages: Different productivity characteristics
  • Prototyping: Exploratory development

Calibration Guidelines

Organizational Calibration

  1. Collect historical data from completed projects
  2. Calculate actual vs. predicted ratios
  3. Adjust model constants based on organizational factors
  4. Validate calibration on new projects
  5. Update regularly as organization matures

Industry-Specific Adjustments

  • Financial services: +20-30% for regulatory compliance
  • Healthcare: +30-40% for safety requirements
  • Embedded systems: +40-60% for hardware constraints
  • Web applications: -10-20% for rapid development tools

COCOMO models provide a systematic approach to estimation but require calibration to organizational and project-specific factors for maximum accuracy.