How Do You Write Design Specifications?

Write design specifications as clear, justified, and testable criteria that a successful design must satisfy. Each criterion should come from research into the user, context, and constraints rather than personal preference.

Building Effective Specifications

In B2.1 The design process, specifications translate research and analysis into criteria for developing and evaluating design ideas. They define what the outcome must achieve without prescribing one final solution.

A strong specification contains three elements:

1. Requirement: What the design must achieve.
2. Justification: Why the requirement matters, supported by research.
3. Testing method: How compliance will be checked objectively.

Instead of writing “The chair must be comfortable,” write: “The seat height must be adjustable between $400\text{ mm}$ and $520\text{ mm}$ to accommodate the anthropometric range identified in target-user research; this will be tested using a measuring tape and user trials.”