Technology Readiness Levels (TRL) Explained: 9-Level Reference Guide

What TRL measures

Technology Readiness Levels are a scale for how mature a technology is. They run from TRL 1, basic research, to TRL 9, a technology in everyday use. Innovate UK, UKRI, the Aerospace Technology Institute and most other UK funders use the same nine-level scale when they ask applicants to state the starting and target TRL of a project.

The level is not a measure of how clever the idea is. It measures evidence: how far the technology has been proven in a real or representative environment. That is why the same product can contain components at very different TRLs.

TRL quick reference: the nine levels

TRL 1: basic principles observed and reported.

TRL 2: technology concept or application formulated.

TRL 3: experimental proof of concept demonstrated.

TRL 4: technology validated in a laboratory environment.

TRL 5: technology validated in a relevant environment.

TRL 6: system or subsystem demonstrated in a relevant environment.

TRL 7: system prototype demonstrated in an operational environment.

TRL 8: actual system completed and qualified through test and demonstration.

TRL 9: actual system proven in successful operational service. The sections below explain what each level looks like in practice for a UK grant application.

TRL 1 to 3: from idea to proof of principle

TRL 1 is basic research. The underlying principles are being observed and reported, often in academic literature, but no one has yet tried to apply them to the specific problem.

TRL 2 moves into applied research. A team starts to formulate how the research might become a practical solution, usually on paper or in simulation.

TRL 3 is proof of concept or proof of principle. An experiment or model shows that the key idea can work in a controlled setting. For example, a new battery chemistry might demonstrate the expected voltage and cycle life in a coin cell made by hand in a lab. It is not yet a product, but the uncertainty has moved from whether the science works to whether it can be engineered.

TRL 4 to 6: validation in the lab and beyond

TRL 4 is technology validation in a laboratory environment. The component or subsystem is built and tested under controlled conditions that mimic some aspect of the final application. A sensor might be validated on a bench with synthetic samples rather than in a real process line.

TRL 5 is validation in a relevant environment. That usually means real materials, real operating conditions, or integration with other real subsystems. A medical device prototype might be tested with ex vivo tissue or early clinical samples rather than just simulant.

TRL 6 is system or subsystem demonstration in a relevant environment. The technology is now being shown as part of a realistic system. For a robotics project, this could be a prototype operating on a factory-like test rig rather than in a clean lab bay.

TRL 7 to 9: demonstration, deployment and use

TRL 7 is system prototype demonstration in an operational environment. The technology works in the setting where it is meant to be used, even if the product itself is not yet final. An agri-tech sensor might be trialled on several real farms across a growing season.

TRL 8 is the actual system completed and qualified through test and demonstration. The product is essentially finished and has been shown to meet its specification under operational conditions.

TRL 9 is the system proven in successful operational service. It is in use with paying customers or end users, with performance data from the field. Very few grant-funded projects aim for TRL 9 within the grant period; most stop at TRL 6, 7 or 8 and leave the final scale-up to commercial investment.

Why a new project in a mature product can still be low TRL

Founders often assume that because their company has a mature product, any new project they propose must be high TRL. That is a costly mistake. A new sensor, algorithm, manufacturing process or formulation added to an existing platform starts its own TRL journey from the bottom.

Imagine a company with a TRL 8 medical imaging device. The team wants to add a new AI reconstruction module. The device is mature, but the module is at TRL 3 or 4: it has shown promise in offline testing but has not been integrated into the live imaging workflow. The grant application should describe the project as starting at TRL 3 and targeting TRL 6 or 7, not as a minor upgrade to an already-commercial platform.

Assessors reward honesty here. Claiming a high starting TRL for unproven work damages your credibility. Claiming a low starting TRL for work that is already well evidenced wastes the project's apparent ambition.

How assessors judge TRL in grant applications

Assessors rarely take your stated starting TRL at face value. They check it against the evidence elsewhere in the application: the track record of the team, what has actually been built, what testing has been done and with whom. A claim of TRL 5 with no named trial partner, no test data and no prototype photographs reads as TRL 2 or 3.

Three things move an assessor's view of your starting TRL. First, integration evidence: has the technology run inside or alongside a real system, or only on a bench? Second, environment evidence: has it faced real materials, real users or real operating conditions, or simulations and synthetic data? Third, independent evidence: has anyone outside your team validated a result, such as a trial partner, a test house or a prospective customer?

Consider two applications for the same TRL 4 to TRL 7 competition. One states that its sensor is at TRL 4 and will reach TRL 7 through a workpackage called 'demonstration'. The other states that its sensor has been validated at TRL 4 on a bench with synthetic samples, has a signed trial agreement with a water utility to test on two live treatment works in months 7 to 18, and will reach TRL 7 through that trial plus a certification pathway with a named test house. The second application scores higher because the TRL claim is falsifiable and evidenced.

TRL claims also interact with your route to market. If you claim you will reach TRL 8 in 24 months, assessors expect to see who certifies the system, who buys the first units and what the manufacturing plan is. A target TRL without a route to it is treated as an ambition, not a plan.

Writing the TRL section of your Innovate UK application

Innovate UK application forms usually give you a question on the current state of the technology, sometimes alongside a question on the target state at project end. Weak answers name the level only. Strong answers give the level, the evidence for it, and the work that will move it to the target level.

A strong starting-TRL statement looks like this: 'The technology is at TRL 4. A working prototype has been validated in laboratory conditions against BS EN test protocols, with results independently reviewed by the National Physical Laboratory. It has not yet operated in a live environment, which is the purpose of workpackage 2.' Compare that with a weak version: 'Our technology is at TRL 4 and will be TRL 7 by the end of the project.' The first tells the assessor what exists and what does not. The second tells them nothing.

Match your target TRL to the competition brief. If a Collaborative R&D call asks for projects starting at TRL 3 and ending at TRL 6, a project proposing to reach TRL 8 will be marked down for scope, not ambition. Equally, a project already at TRL 6 applying to a TRL 3 to 6 call is likely to be judged as low innovation.

Finally, keep the TRL story consistent across the whole application. The state-of-the-art answer, the project description, the workpackage descriptions and the risk register should all agree on the starting and target levels. Assessors read every question, and an internal contradiction on TRL is one of the fastest ways to lose marks on project assurance.

How funders use TRL

Most Innovate UK competitions specify an eligible starting and target TRL range. A Collaborative R&D call might want projects that start at TRL 3 and reach TRL 6. An EIC Accelerator project might need to start at TRL 5 or above and reach TRL 7 or 8. If your project sits outside the range, it is usually ineligible regardless of how good the idea is.

TRL also shapes the budget and the risk profile. Lower TRL projects need more research spend and carry higher technical risk. Higher TRL projects need more demonstration and scale-up spend, and the risk shifts towards market and manufacturing execution.

UKRI publishes a clear table of the activities associated with each TRL, which is a useful reference when you are deciding where your project honestly sits.

TRL is only half the story

A technology can reach TRL 7 and still fail because no one will pay for it. That is where Commercial Readiness Levels come in. TRL answers whether the technology can work. CRL answers whether a customer will buy it, whether the market is understood, and whether the business model is proven.

If you are preparing a grant application, state your TRL clearly and honestly, then use the rest of the application to show that the commercial readiness is rising alongside the technical readiness. We cover the commercial side in our companion article on Commercial Readiness Levels.

Sources and further reading

UKRI publishes a table of the activities typically associated with each TRL, which is the reference most UK funders follow. The Aerospace Technology Institute also provides applicant guidance on the nine-level scale. For the commercial side, see our article on Commercial Readiness Levels, which draws on the Curtinnovation Readiness Levels and KTH Innovation Readiness Level model.