What Is the Difference Between FAT, SAT, and UAT?
Each test serves a different purpose and takes place at a different stage. Understanding the distinction helps reduce acceptance risk.
FAT, SAT, and UAT are common terms in engineering, technology, automation, infrastructure, and IT projects. Although all three relate to testing and acceptance, they serve different purposes and normally occur at different stages of the project lifecycle.
FAT — Factory Acceptance Test
FAT is generally performed before equipment or systems leave the manufacturer or assembly facility. Typical objectives include verifying that equipment complies with specifications, critical functions operate correctly, basic configuration is correct, and major defects are identified before shipment.
SAT — Site Acceptance Test
SAT is performed after the system has been installed at the actual operating location. It typically verifies installation, power, network, interfaces, communications, site environment, integration, and performance under actual site conditions.
UAT — User Acceptance Test
UAT evaluates the system from the perspective of actual users and business or operational processes. The key question is no longer simply “Does the system function?” but “Does the system support the real user and business requirements that were agreed?”
- User workflows
- Business processes
- Permissions
- Reporting
- Usability
- Real operational scenarios
- Exception cases
The Difference at a Glance
FAT
Location: Manufacturer / Factory
Focus: Product or system before shipment
“Was the system built according to the specification?”
SAT
Location: Actual site
Focus: Installation, integration, and site environment
“Does the system operate correctly after installation?”
Primary perspective: End user
Focus: User and business requirements
“Does the system support actual operational use?”
Passing Tests Does Not Always Mean the System Is Ready for Final Acceptance
- Outstanding defects
- Punch-list items
- Documentation
- Training
- Backup arrangements
- Cybersecurity
- Spare parts
- Warranty
- Support contacts
- Maintenance plans
- Operational readiness
Conclusion
FAT → verifies what was built, SAT → verifies what was installed, UAT → verifies what users actually need to use. When these stages are linked to requirements and acceptance criteria established earlier in the project, the final acceptance decision becomes more evidence-based, traceable, and defensible.