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Specify Requirements

Key Info

  • Design requirements state the important characteristics that your design must meet in order to be successful.
  • One of the best ways to identify the design requirements for your solution is to use the concrete example of a similar, existing product, noting each of its key features. Here is how to analyze:
  • To complete the requirements step of the design process, you should write a design brief; a document that holds all of the key information for solving your problem in one place. Here is a Design Brief Worksheet to help you develop your own.

Design Requirements

Design requirements state the important characteristics that your solution must meet to be successful.

For example, imagine that your problem statement relates to grocery store bags. You want to design a better grocery store bag--one that uses less expensive material than the paper and plastic bags that already exist. Your design requirements are the important characteristics that your bag must meet to be successful. Based on your problem statement, a successful bag would use less expensive material than existing bags and function properly as a grocery bag. Examples of some of your design requirements might be that the bag needs to:

  • Have handles so that shoppers can carry multiple bags of groceries.
  • Hold up to five pounds of food without breaking.
  • Cost less than five cents to make.
  • Collapse so that it can be stored in large quantities at grocery stores.

Effective design requirements are:

  • Needed to solve your design problem. If it is not needed, leave it out. You'll have enough other things to work on!
  • Feasible. A good design requirement is not just a wish. Ask if you have the time, money, materials, tools, and knowledge to make it happen.
  • Subject to change as you do more research and design. Always ask yourself, is this requirement needed and feasible? If your answers to those questions change, it is OK to change the requirement.

Design requirements can fall into many different categories, such as size, cost, ease of use, and environmental impact, to name just a few. Here is a more complete list of Design Requirement Examples.

One of the best ways to identify the design requirements for your project is to use the concrete example of a similar, existing product. Examine it in detail-take pictures, and take it apart if you have permission. Analyze how and why it works the way it does. Every single feature of the existing project represents a potential requirement for your design. (Of course, your design will have changes and improvements, so the requirements will not be identical.)

When you analyze an existing product, you build a mental library of techniques, mechanisms, and clever tricks. You acquire building blocks that you can use to construct your own designs. As you analyze more products, you can gain additional building blocks to use in your design. All designers do this!

These examples show how to analyze an existing product:

How many design requirements should you have? For a school project, three to five will often be a good number. For large, complex projects, there may be hundreds or even thousands of requirements. Here is more information about How Many Design Requirements? you should have.

First, as a group, your list of design requirements should provide a complete description of the key features that will make your design successful. Ask yourself, is anything missing?

Second, as a group, your list of design requirements should be feasible. Individually, your requirements might be feasible, but all together they might not be. For example, you might have time (or money or resources) to make one of them happen, but not all of them. Another potential problem might be that it is impossible to meet two or more of your requirements at the same time. For example, imagine that you are designing a toaster for a bagel shop. Two of your design requirements might be that the toaster needs to be large enough to toast ten bagels at a time, and it needs to fit on the bagel shop's counter. What if a toaster large enough to hold ten bagels at a time will not fit on the shop's counter? In cases like this, you must make a trade-off, a compromise or change in one or more requirements so that they can be met at the same time. In the toaster example, you would need to decide which is more important: toasting ten bagels at once or fitting the toaster on the counter? If the changes to your requirements make it impossible to solve your problem, you should look for a different problem to work on.

The Design Brief

To complete the requirements step of the design process, you should write a design brief. A design brief gathers all the key information for solving your problem in one place. It should contain:

  • A description of your target user.
  • A definition of the problem you intend to solve. [Who] need(s) [what] because [why].
  • A description of how existing products are used and why they fail to address the problem.
  • A list of all the requirements for your design.

For complex products with dozens of requirements or more, engineers supplement the design brief with detailed specifications such as a product requirements document (PRD) or a product design specification (PDS).

Design Brief Worksheet

Here's a Design Brief Worksheet to help you develop your own.

Design Brief Checklist

Answer the questions in the quick checklist below to grade your design brief.

What Makes a Good Design Brief? For a Good Design Brief, You Should Answer "Yes" to Every Question
Does it define the problem you intend to solve? [Who] need(s) [what] because [why]. Yes / No
Does it describe how existing products are used and why they fail to address the problem? Yes / No
Does it describe your target user? Yes / No
Does it list all of the requirements for your design? Yes / No
Is each design requirement needed to solve your problem? If it is not needed, leave it out. You'll have enough other things to work on! Yes / No
Is each design requirement feasible? Ask if you have the time, money, materials, tools, and knowledge to make it happen. If you have conflicts between your requirements, have you investigated making trade-offs among them? Yes / No