Specification Limits

The allowable range around the process mean on a control chart that represents the customer's required performance for a product or service. This requirement-based band can be wider or narrower than the statistical control limits.

Key Points

  • Set by the customer, contract, or standard and expressed as LSL (lower specification limit) and USL (upper specification limit).
  • Different from control limits, which are calculated from process variation and show statistical control.
  • May be tighter or looser than control limits; a process can be in control yet still produce outputs outside specs, or vice versa.
  • Used in capability analysis (e.g., Cp, Cpk) to judge whether the process can consistently meet requirements.

Example

A machining process targets a 10.00 mm shaft diameter. The customer specifies 9.95 mm (LSL) to 10.05 mm (USL) as acceptable. The control chart shows the process mean at 10.00 mm with control limits based on natural variation at 9.92 mm and 10.08 mm. Even if the process is stable (within control limits), parts between 10.05 mm and 10.08 mm are out of spec and must be reworked or rejected.

PMP Example Question

Which statement best describes specification limits in quality management?

  1. The statistically computed boundaries (about +/-3 sigma) that indicate expected process variation.
  2. The customer-defined tolerance band that determines which outcomes are acceptable (LSL and USL).
  3. The approved range of the project budget variance allowed by the sponsor.
  4. The set of thresholds used to categorize risks on a probability-impact matrix.

Correct Answer: B — Customer-defined tolerance band (USL and LSL)

Explanation: Specification limits reflect customer or standard requirements, while control limits reflect process behavior based on statistical variation.

AI-Prompt Engineering for Strategic Leaders

Stop managing administration and start leading the future. This course is built specifically for managers and project professionals who want to automate chaos and drive strategic value using the power of artificial intelligence.

We don't teach you how to program Python; we teach you how to program productivity. You will master the AI-First Mindset and the 'AI Assistant' model to hand off repetitive work like status reports and meeting minutes so you can focus on what humans do best: empathy, negotiation, and vision.

Learn the 5 Core Prompt Elements-Role, Goal, Context, Constraints, and Output-to get high-quality results every time. You will build chained sequences for complex tasks like auditing schedules or simulating risks, while navigating ethics and privacy with human-in-the-loop safeguards.

Move from being an administrative manager to a high-value strategic leader. Future-proof your career today with practical, management-focused AI workflows that map to your real-world challenges. Enroll now and master the language of the future.



Become an AI-First Agile Leader!

HK School of Management empowers you to master AI as your most powerful co-pilot—without the complexity. Transform your agile leadership with practical, prompt-based workflows and proven strategies designed for real-world scrum challenges. For the price of lunch, you get the tools to automate mundane tasks, refine backlogs with precision, and drive unprecedented efficiency in your team. Backed by our 30-day money-back guarantee—zero risk, real impact.

Learn More