When to use: Use for NFPA 13 density/area method preliminary hydraulic calculations. Select occupancy hazard class to get the required design density (GPM/ft²) and remote design area, then compute total system water demand including hose allowance. Use to size fire pumps, city connections, and determine if available water supply meets NFPA 13 requirements. Full hydraulic calculations require computer software per NFPA 13.