Design Specifications
Definition
Design Specifcation
A design specification is a detailed list of requirements, constraints, and important considerations that a product must meet.
The Role of Design Specifications
- Translate research findings into actionable design criteria.
- Define the boundaries of the solution.
- Allow for clear evaluation and testing of the final product.
- Ensure the product meets both user needs and technical feasibility.
Note
Design specifications are not just technical requirements. They also include aesthetic, ergonomic, and sustainability considerations.
Constructing Design Specifications
Step 1 - Conduct Research
- Primary Research: Use interviews, surveys, observations, and user testing to understand needs directly from users.
- Secondary Research: Analyse existing products, material data, safety standards, and industry trends to provide wider context.
Step 2 - Identify Success Criteria
- Essential Criteria: Critical for function, safety, and usability. Without these, the product fails to meet its purpose.
- Desirable Criteria: Non-critical features that improve comfort, appeal, or convenience based on user preferences.
Step 3 - Prioritise Criteria
- Not all specifications carry the same weight.
- Rank each specification as High, Medium, or Low priority.
- Consider importance to the user, technical feasibility, cost, and production limits.
- Be ready to make trade-offs if needed during development.
Step 4 - Document Specifications
- Record your criteria clearly and measurably.
- Use concise, unambiguous language.
- Include measurable terms (e.g. “under 500g”, “IPX4 water-resistant”, “fit in a 30x20 cm space”).
- Link each specification back to your research findings.
Tip
Avoid vague terms like "around" or "approximately." Instead, use clear and measurable values. For example:
- Say "maximum of 100 cm" instead of "around 1 meter"
- Use "between 90–95 cm" or "90 cm ±1 cm" to show acceptable ranges
| Poorly Written Specification | Well Written Specification |
|---|---|
| The overall width of the product must be 50mm. | The overall width of the product must be between 40 and 50mm to reflect the 50th percentile user. |
| The product should be aesthetically pleasing. | The aesthetics of the product must appeal to the target audience of students aged 15–24 years. |
| The aesthetics of the product must appeal to the target audience of students aged 15–24 years. | The height of the product must be 90mm ±1mm to ensure suitability to the client. |
| The material should be wood as it's most suitable for the outdoors. | 4.1: The material must be lightweight, with a maximum weight of 20kg to allow easy transport. / 4.2: The material must be durable and moisture-resistant for outdoor use. |
| The chair should be suitable for the 50th percentile. | 5.1: The width of the chair seat must be between 400 mm and 420 mm to comfortably accommodate the 50th percentile user. / 5.2: The height of the chair seat must be between 430 mm and 460 mm to ensure ergonomic seating posture for the average adult. |
| The target market is everyone who sits on a chair. | The target market is elderly people aged 70+ who need extra comfort and support. |
| The product should work correctly. | The product must reduce water usage by at least 50%. |
| The product should be easy to use. | The force required to turn the product must not exceed [X] Nm of torque. |
Example
- Specification: The product must weigh no more than 500 grams to ensure portability for daily use.
- Type: Essential
- Priority: High
- Justification: Based on user interviews, 85% of respondents reported discomfort carrying heavier models during extended periods, particularly students and commuters.
Self review
Identify three essential and three desirable criteria for a product you use daily.
