Function Points Cheat Sheet
Quick reference for Function Point Analysis (FPA) including counting rules, complexity assessment, and calculations.
Function Point Components
1. External Inputs (EI)
Definition: Data or control information provided by the user to the application
Examples:
- Add customer record
- Update inventory item
- Delete employee
- Login authentication
- File upload
Complexity Assessment:
| Complexity | Data Elements | File Types | Complexity Points |
|---|---|---|---|
| Low | 1-4 | 0-1 | 3 |
| Average | 5-15 | 2 | 4 |
| High | 16+ | 3+ | 6 |
2. External Outputs (EO)
Definition: Data or control information sent to the user from the application
Examples:
- Customer report
- Invoice generation
- Email notifications
- Dashboard charts
- Export files
Complexity Assessment:
| Complexity | Data Elements | File Types | Complexity Points |
|---|---|---|---|
| Low | 1-5 | 0-1 | 4 |
| Average | 6-19 | 2-3 | 5 |
| High | 20+ | 4+ | 7 |
3. External Inquiries (EQ)
Definition: Online inputs that result in the retrieval of data
Examples:
- Customer lookup
- Product search
- Account balance inquiry
- Order status check
- Help system queries
Complexity Assessment:
| Complexity | Data Elements | File Types | Complexity Points |
|---|---|---|---|
| Low | 1-5 | 0-1 | 3 |
| Average | 6-19 | 2-3 | 4 |
| High | 20+ | 4+ | 6 |
4. Internal Logical Files (ILF)
Definition: User identifiable group of logically related data maintained within the application
Examples:
- Customer master file
- Product catalog
- Employee records
- Order database
- Configuration settings
Complexity Assessment:
| Complexity | Record Types | Data Elements | Complexity Points |
|---|---|---|---|
| Low | 1 | 1-19 | 7 |
| Average | 2-5 | 20-50 | 10 |
| High | 6+ | 51+ | 15 |
5. External Interface Files (EIF)
Definition: User identifiable group of logically related data used by the application but maintained by another application
Examples:
- Third-party payment gateway
- External user directory
- Vendor catalog feeds
- Government tax tables
- Partner inventory systems
Complexity Assessment:
| Complexity | Record Types | Data Elements | Complexity Points |
|---|---|---|---|
| Low | 1 | 1-19 | 5 |
| Average | 2-5 | 20-50 | 7 |
| High | 6+ | 51+ | 10 |
General System Characteristics (GSC)
Rate each characteristic from 0-5:
- 0: No influence
- 1: Incidental influence
- 2: Moderate influence
- 3: Average influence
- 4: Significant influence
- 5: Strong influence throughout
GSC Factors
| # | Characteristic | Weight | Description |
|---|---|---|---|
| 1 | Data Communications | 1 | Distributed processing, online data entry |
| 2 | Distributed Data Processing | 1 | Application runs on multiple processors |
| 3 | Performance | 1 | Response time, throughput requirements |
| 4 | Heavily Used Configuration | 1 | Utilization of computing resources |
| 5 | Transaction Rate | 1 | How frequently transactions are executed |
| 6 | Online Data Entry | 1 | Interactive input of data |
| 7 | End-User Efficiency | 1 | Human factors, ease of use |
| 8 | Online Update | 1 | Online update of internal logical files |
| 9 | Complex Processing | 1 | Complex algorithms, extensive calculations |
| 10 | Reusability | 1 | Code designed and developed for reuse |
| 11 | Installation Ease | 0.5 | Ease of installation and setup |
| 12 | Operational Ease | 0.5 | Automated operations, error recovery |
| 13 | Multiple Sites | 1 | Application designed for multiple locations |
| 14 | Facilitate Change | 1 | Ease of modification and enhancement |
Calculation Process
Step 1: Count Unadjusted Function Points (UFP)
UFP = (EI × 3/4/6) + (EO × 4/5/7) + (EQ × 3/4/6) + (ILF × 7/10/15) + (EIF × 5/7/10)
Step 2: Calculate Total Degree of Influence (TDI)
TDI = Σ(GSC Rating × Weight) for all 14 characteristics
Step 3: Calculate Value Adjustment Factor (VAF)
VAF = 0.65 + (TDI × 0.01)
Range: 0.65 to 1.35
Step 4: Calculate Adjusted Function Points (AFP)
AFP = UFP × VAF
Counting Guidelines
What to Count as Separate Functions
External Inputs (EI):
- Different logical files updated
- Different processing logic
- Different input formats
- Different validation rules
External Outputs (EO):
- Different report formats
- Different calculations
- Different data sources
- Different selection criteria
External Inquiries (EQ):
- Different search criteria
- Different display formats
- Different data sources
- Different access levels
What NOT to Count
- Error messages (part of primary function)
- Help text (unless complex help system)
- System administration functions (unless user-requested)
- Duplicate reports with minor format differences
- Navigation elements (menus, buttons)
Data Element Counting
Count as Data Elements
- User recognizable fields
- System-generated fields (timestamps, IDs)
- Foreign keys when displayed to user
- Calculated fields displayed to user
- Control information (action codes, function keys)
Do NOT Count as Data Elements
- Literal values, headings, titles
- Paging information
- Physical implementation fields not visible to user
- Derived attributes stored for performance only
File Type Counting
Count as File Types Referenced
- Master files read/updated
- Transaction files processed
- Reference tables accessed
- Control files used
- Interface files accessed
Logical vs. Physical Files
- Count logical files, not physical implementation
- Related tables that represent single logical entity = 1 file type
- Junction/intersection tables usually don’t count separately
Common Estimation Patterns
Typical Function Point Distribution
| Component | % of Total FP | Typical Range | |———–|—————|—————| | EI | 20-30% | Simple forms and updates | | EO | 15-25% | Reports and exports | | EQ | 10-20% | Searches and lookups | | ILF | 30-50% | Core business entities | | EIF | 5-15% | External system interfaces |
Complexity Distribution Guidelines
| Complexity | Typical % | When to Use | |————|———–|————-| | Low | 35% | Simple, straightforward functions | | Average | 50% | Standard business functions | | High | 15% | Complex, multi-step processes |
Quick Estimation Techniques
Early Estimation (Requirements Phase)
- Count major business entities → estimate ILFs
- Identify key user processes → estimate EIs
- List important reports → estimate EOs
- Consider search/inquiry needs → estimate EQs
- Identify external systems → estimate EIFs
Rough Sizing Formula
Rough FP = (# of Inputs × 4) + (# of Outputs × 5) + (# of Files × 10) + (# of Interfaces × 7)
Conversion to Other Metrics
Function Points to Lines of Code
See Productivity Benchmarks for language-specific conversion rates
Function Points to Development Effort
| Application Type | Hours per FP | Range | |——————|————–|——-| | Business Applications | 10-20 | Standard complexity | | Web Applications | 8-16 | Modern frameworks | | System Software | 15-30 | High complexity | | Real-time Systems | 20-35 | Embedded constraints |
Quality Assurance Checklist
During Counting
- All user-requested functions identified
- Complexity consistently assessed
- Data elements properly counted
- File references validated
- No double-counting of functions
Final Review
- Function point distribution reasonable
- Complexity distribution follows guidelines
- GSC ratings justified and documented
- Calculations verified
- Results compared to similar projects
Common Pitfalls
Over-counting
- Counting technical functions not visible to users
- Double-counting related functions
- Counting every screen as separate function
- Including infrastructure/framework functions
Under-counting
- Missing batch processing functions
- Forgetting interface/integration functions
- Underestimating complexity factors
- Missing control/administrative functions
Complexity Errors
- All functions rated as “Average”
- Not considering data element counts
- Ignoring file reference counts
- Inconsistent complexity criteria
Function Point Analysis requires practice and consistency. When in doubt, document assumptions and maintain counting standards across projects.