Structural Design

Functional Requirement

A functional requirement describes what a system, product, service, or component must do to support a user, business, or operational need.

Concept facts

A functional requirement describes what a system, product, service, or component must do to support a user, business, or operational need.

Also known as
System function, feature requirement, behavioural requirement, capability requirement.
Used in
Requirements engineering, product delivery, software development, service design, acceptance criteria, QA, and release planning.
Interpret with
User requirement, business requirement, non-functional requirement, acceptance criteria, use case, user story, and release readiness.

Plain-language explanation

A functional requirement states a required behaviour or capability. Functional requirements help delivery teams understand expected actions, flows, rules, and system responses.

Why it matters

Functional requirements turn needs and policy decisions into buildable service behaviour. If unclear, teams may implement the wrong capability or miss important conditions.

Use contexts

  • specifying system or service capabilities
  • planning forms, dashboards, workflows, and integrations
  • defining actions users or staff can perform
  • describing eligibility, verification, payment, or status functions
  • preparing acceptance criteria

Application guidance

Write functional requirements in clear, testable language. State who or what performs the action, what the system must do, and under what conditions. Check edge cases and exception flows.

Practical example

A public grievance portal needs to route complaints to the correct municipal department. A functional requirement states: “The service must assign each submitted complaint to a department based on selected issue type and location.” The UX consequence is fewer wrongly routed complaints, reduced staff triage burden, faster operational response, and better citizen trust.

Interpretive boundaries

A functional requirement should not be confused with a design mockup, user story, or acceptance criterion. It says what must happen, but not always exactly how the interface should look.

Applied at Userhub

Userhub uses functional requirements to connect research findings, user needs, business rules, and delivery decisions. In UX Lab work, functional-requirement review helps identify gaps between intended service behaviour and real user task success.

See Userhub UX Lab for applied UX research and evaluation context.

Sources and references

ISO/IEC/IEEE. (2018). ISO/IEC/IEEE 29148:2018 Systems and software engineering — Life cycle processes — Requirements engineering. International Organization for Standardization. https://www.iso.org/standard/72089.html

Wiegers, K., & Beatty, J. (2013). Software requirements (3rd ed.). Microsoft Press.

International Institute of Business Analysis. (2015). A guide to the Business Analysis Body of Knowledge (BABOK Guide) (Version 3). International Institute of Business Analysis.

Cite this entry

APA

Userhub. (2026). Functional Requirement. UX Reference. https://userhub.com.bd/reference/functional-requirement/