Everyone knows that a Requirements Document (RD) is one of the keys to developing a product that has product market fit. Without product market fit, a positive ROI is very unlikely.
But what exactly should be in a RD? The answer is simple but not easy: everything that is necessary for the product to have product market fit. True, but it is not very useful, so here is a list of the categories that are most often in RD we develop:
Functional Requirements: What functions must the product perform.
Performance: How well must the product perform these functions.
Compliance: Does the product need to conform to any standards: FCC, UL, CE, etc.
Environmental: What environment does the product need to operate in: temperature, vibration, shock, etc.
Power: If the product is electronic, how will it be powered
Input/Outputs: What comes into the product (UI, signals, etc.) and what comes out.
Costs: Unit Cost/COGS, development budgets, total cost of ownership, etc.
Schedules: When does everything have to be completed by
Typically each requirement is numbered and lists the testing method that is acceptable for proving that the product does meet the requirement and gets everyone on the same page about the Design Verification Test.
BTW, our Requirements Document Template is here.