Write A Good Product Requirements Specification

Updated: Jan 28, 2020

From Idea to Success

Product requirements specification (PRS) or Product requirements document (PRD) is one of the most important documents in the hardware development process. PRS defines how professionally, qualified (these need to be adverbs but qualified doesn’t have a smooth transition here) and fast you will develop your product. Our practice shows that a well-prepared PRS saves time and client (not the client’s) money. "Many engineers waste time and effort because they don’t have a clear technical specification of their product. They start with the design and keep adjusting as they discover more. They end up redoing part of the design because old architecture does not hold good for the new requirements. This is a huge waste of time, effort and cost."

1. If you think that you have already adequately described your product, that’s most likely not the case. In 8 of 10 cases, we receive just a few sentences as product description/requirements and the client thinks that it's all the information needed for the development. But once the client understands the necessary but unmentioned details, the document size easily increases 10, 20 fold or more. 2. Even really small details matter. When it comes to professional development, many of the details which may seem unimportant at first glance - make a huge difference here. The shape of the product, placement of a button or color of the LED may have a significant impact on development, so make sure that you included even the smallest details. 3. Even if you think you have described everything well - draw it. The visual effect can show much more than a dry text description, so include as many possible links, photos, videos and drawings in PRS to describe functions, placement, behavior or even competitors’ products. 4. Know your product. When it comes to consumer electronics or other devices that interacts with a human, you really want to know your customer as well as possible. One thing that distinguishes a good product from just an ordinary product is understanding how this product is going to be used in daily life. Even a “idiot-proof“ feature can make your device more robust and protect it from frequent and even negligent use. Customers like devices that are not easily broken. Because a good engineer is also a good adviser, we often must show a client potential weaknesses and possible improvements in design. 5. Don't rush - double check to confirm you haven’t missed any details. There is always some missing information in your first version but in your interest, it is best to keep that list of missing details as short as possible. As we said in the beginning - a thorough PRS saves time and money. All too often, when clients receive the first prototype that is when they recognize how many details were missed.

Remember - don’t rush and make sure you list every detail. 6. Describe all peripheral parts. The best-case scenario when something is connected or inserted into a device is to make sure you have described this part in detail. Often devices have a USB connection, battery or power supply connection. Check if you added all the specs and datasheets of each connected part.

7. Do not ask silly questions. The real life example of silly request - "I want to make a vape with 4 heads into one body and also controlled by Bluetooth. Moreover, the temperature can be controlled too. Feel free to ask any questions you have." All the professionals will skip your request because no one wants to spend their time when you don't want to spend yours. You need to understand that good estimates (time and budget) require our time which is usually free of charge. 8. Ask smart questions. It's normal if you don't know some of the technical details or how to define requreiments. What we usually suggest to do is to put questions aside from the information you know and during review we can clearly see them and easily answer on them. In case if you are not confident in some decisions you may indicate that we can define those parts by our self. 9. Describe deliverables. Clearly describe what exactly you expect as the output of development process. This is a mandatory part which must be included in any PRS, so make sure you created a list of outputs and tasks. 10. Add mechanical design requirements. Most of the cases you have any requirements to the size or shape, position, physical specifications of any electronic part or PCBA itself. This is mostly related to mechanical designer and you may consider having one during design process. We usually provide a STEP file of PCBA which you can use for validation of overall design. This is quite helpful to check that everything fits inside construction.

11. Add preferred and max/min allowed specs.

Sometimes you might have challenging requirements which could be not achievable, so what we recommend to do is to specify the best and worst-case scenario which still can be acceptable for you. That will help us to understand how flexible is your PRS and suggest you the optimal solution.


It's pretty much all we wanted to point your attention and below you can find attached template where you just need to fill required details. We hope you liked this post and waiting for your requests. Pulse Prototyping LTD. Link for downloading.