Critical Ratio

Critical ratio is the dispatch priority metric that compares remaining time until due date with remaining processing time - it highlights lots at highest risk of tardiness.

What Is Critical ratio?

• Definition: Ratio calculated as time remaining to due date divided by remaining work content.
• Interpretation: Values below one indicate likely lateness without priority intervention.
• Decision Role: Lower critical ratio generally receives higher dispatch priority.
• Scope Use: Applied in due-date focused scheduling and service-level control.

Why Critical ratio Matters

• Lateness Prevention: Prioritizes at-risk lots before due-date miss occurs.
• Objective Alignment: Directly supports on-time delivery performance targets.
• Transparency: Provides interpretable urgency score for operators and planners.
• Dynamic Responsiveness: Priority automatically changes as time and queue conditions evolve.
• Portfolio Control: Helps balance urgent and normal lots with quantifiable logic.

How It Is Used in Practice

• Real-Time Calculation: Recompute ratios continuously as queue and due-date states update.
• Rule Integration: Combine with setup and queue-time constraints in weighted dispatch engines.
• Escalation Bands: Define critical-ratio thresholds for automatic hot-lot promotion.

Critical ratio is a practical urgency metric for due-date driven dispatching - ratio-based prioritization improves tardiness control and strengthens delivery reliability in dynamic fab environments.