TRL 4 vs TRL 5 vs TRL 6: What Is the Difference?

By Dr. Ahmed Mortuza Saleque · Updated November 11, 2026 · How we check our content

The short answer

TRL 4 means the components work together in the lab. TRL 5 means those components have been validated under realistic conditions, called a relevant environment. TRL 6 means a representative prototype of the whole system, not just its components, has been demonstrated in that relevant environment. So 4 to 5 changes the environment, and 5 to 6 changes components into a system.

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Comparison of TRL 4, TRL 5 and TRL 6 showing what is tested, where it is tested and an example for each level — Tap the image to enlarge it. Free to share with a link to this page.

Side by side

	TRL 4	TRL 5	TRL 6
What is tested	Components or breadboard	Components at higher fidelity	Representative prototype system
Where	Laboratory	Relevant environment	Relevant environment
Fidelity	Low: lab parts, ad hoc set-up	Medium: closer to real parts	High: close to final form
Typical evidence	Bench test report	Test report under realistic conditions	Prototype demonstration report

What is a relevant environment?

A relevant environment reproduces the conditions that matter most for the technology, without being the real place of use. For a sensor that goes on a ship, it might be a salt-spray chamber and a vibration table. For software, it is realistic data volumes and loads on hardware like the real system. For a medical device, it might be an animal model or a simulated clinical setting.

The operational environment is the real setting, and testing there is what TRL 7 requires.

Example: a crop-monitoring sensor

TRL 4: the sensor chip, battery and radio are wired together on a lab bench and send readings.
TRL 5: the same components are tested in a climate chamber at field temperatures and humidity, with real soil samples.
TRL 6: a full prototype unit in a weatherproof case runs for a month in a test plot set up to mimic a farm.
TRL 7 would be prototype units working on a real farm through a growing season.

Plot the test readings in the Data Plotter to show reviewers how performance held up as conditions got harder.

Moving up a level

Each step usually costs more than the one before, because test set-ups get more realistic and prototypes get closer to the final design. Plan the tests needed for the next level as work packages on a Gantt chart, and check your current level with the free TRL Assessment before you claim it in a proposal.

Common questions

What is the difference between TRL 4 and TRL 5?

Both test components, but TRL 4 is in the lab and TRL 5 is under realistic conditions in a relevant environment.

What does TRL 6 mean?

A representative prototype system or subsystem has been demonstrated in a relevant environment.

Is a simulation enough for TRL 5?

Usually not on its own. TRL 5 normally needs physical tests under realistic conditions; simulations support the evidence.

What is the difference between TRL 6 and TRL 7?

TRL 6 demonstrates a prototype in a relevant (simulated realistic) environment; TRL 7 demonstrates a near-final prototype in the real operational environment.