Requirements · Comparison
The three common requirements documents compared, what each contains and which one a small project needs.
Last updated: October 2026. Written by Athar Ahmad, Certified Bubble.io Developer and Tech Architect, Simple Automation Solutions.
Quick answer
A BRD (business requirements document) explains why the business wants something and the outcome it needs, a PRD (product requirements document) describes what the product should do, for whom and in what order, and an SRS (software requirements specification) details how the system must behave, often formally. For most small and medium no-code projects a clear PRD with user stories and acceptance criteria is enough; large or regulated systems may need all three.
Key takeaways
- BRD = why; PRD = what; SRS = how, in detail.
- A PRD with user stories and acceptance criteria usually suffices for small projects.
- Good documents are specific, testable, prioritised and state what is out of scope.
- Names are used loosely; check what a document actually contains.
- The $345 Discovery Sprint delivers a PRD within 24 hours.
In this guide
Why are there so many requirements documents?
Projects use several documents with similar names because requirements exist at different levels: why the business wants something, what the product should do and how the system will behave in detail. The three most common are the business requirements document (BRD), the product requirements document (PRD) and the software requirements specification (SRS). Teams and companies use the names loosely, so check what a given document actually contains.
BRD vs PRD vs SRS
| BRD | PRD | SRS | |
|---|---|---|---|
| Full name | Business Requirements Document | Product Requirements Document | Software Requirements Specification |
| Main question | Why are we doing this, and what business outcome do we need? | What should the product do, for whom? | How exactly must the system behave? |
| Typical author | Business owner or analyst | Product owner or founder, with the builder | Technical analyst or engineer |
| Typical content | Goals, benefits, stakeholders, scope, constraints | Users, features, user flows, priorities, scope, success measures | Detailed functional and non-functional requirements, interfaces, data, constraints |
| Level of detail | High level | Medium | High, sometimes formal |
| Typical audience | Executives and sponsors | Product and delivery teams | Engineers and testers |
| Best for | Getting approval and aligning stakeholders | Guiding what is built | Formal or complex systems needing precision |
What does each contain?
Business requirements document
- Problem or opportunity.
- Business objectives and success measures.
- Stakeholders.
- Scope and constraints.
- Expected benefits and costs.
- Risks and assumptions.
Product requirements document
- Product overview and the problem.
- Users and roles.
- First-release scope and what is out of scope.
- User flows and stories.
- Data and rules.
- Integrations.
- Security and platform decisions.
- Success measures, cost and timeline.
Software requirements specification
- Functional requirements, each uniquely identified and testable.
- Non-functional requirements: performance, security, availability, accessibility.
- Interface and integration specifications.
- Data definitions and constraints.
- Acceptance criteria and traceability.
Which do you need for a small project?
For most small and medium no-code projects, a clear PRD is enough: it states what to build, for whom and in what order, in language that both the business and the builder understand. A BRD can be a short section within it, and the SRS-level detail is mostly captured in user stories, acceptance criteria and the data model. Formal SRS documents suit large, regulated or contract-driven projects. See what to cut before you build and our Discovery Sprint.
| Project | Suggested documents |
|---|---|
| Small app or portal | PRD, with user stories and acceptance criteria |
| Medium product with several stakeholders | Short business case, then PRD |
| Large or regulated system | BRD, PRD and SRS, with formal change control |
| Quick prototype | A one-page brief |
What makes any requirements document good?
- Specific enough that two builders would build similar products.
- States what is out of scope.
- Written in plain language.
- Testable: you can tell when each requirement is met.
- Prioritised.
- Kept up to date as decisions change.
What are common mistakes?
- Writing a long document nobody reads.
- Mixing why, what and how without structure.
- Vague words such as fast, easy or intuitive with no measure.
- Skipping the out-of-scope list.
- Treating the document as frozen. Agree a change process. See how to avoid scope creep.
Builds at Simple Automation Solutions start at $3,500, and the $345 Discovery Sprint delivers a PRD within 24 hours, credited toward the build.
Frequently asked questions
What is the difference between a BRD and a PRD?
A BRD explains why the business wants something and what outcome it needs. A PRD describes what the product should do, for whom and in what order.
What is an SRS?
A software requirements specification: a detailed, often formal description of how a system must behave, including functional and non-functional requirements.
Which document do I need for a small app?
Usually a PRD with user stories and acceptance criteria.
Is a PRD the same as a specification?
Not quite. A PRD focuses on what the product does and why. A specification typically goes into more technical detail.
Who writes the PRD?
You supply the business knowledge, and an experienced builder or consultant supplies structure, architecture and a realistic estimate.
Need a requirements document for your project?
Email us your idea. We will help you produce a clear PRD with scope, flows, data and cost.
Athar Ahmad, Certified Bubble.io Developer and Tech Architect, Simple Automation Solutions
About Simple Automation Solutions (SA Solutions)
Simple Automation Solutions is a Bubble.io development studio led by Athar Ahmad, a Certified Bubble.io Developer and Tech Architect. It builds web and mobile apps, client portals and SaaS products for founder-led businesses such as law firms, accounting firms, boutique agencies and consultants. Services include a free 30-minute Idea Audit, a $345 Discovery Sprint (a Product Requirements Document delivered within 24 hours, credited toward the build) and builds starting at $3,500. Website: sasolutionspk.com.
