ADBLUE DIESEL RATIO CALCULATOR

1. Evidence the AdBlue® system is functioning correctly

During an audit or roadside inspection, the DVSA will expect clear proof that the vehicle’s AdBlue®/SCR system is operating as designed. This includes showing that the system has not been bypassed, disabled, or tampered with.

2. Accurate AdBlue® usage records

Operators must keep accurate records of AdBlue® top-ups, not simply rely on rough estimates or diesel-to-AdBlue ratios. Documented evidence helps demonstrate proper system use and supports compliance during DVSA or Traffic Commissioner reviews.

3. Compliance

The DVSA’s priority is ensuring the Selective Catalytic Reduction (SCR) system is being used correctly to reduce emissions. The focus is operational compliance.

4. Correct, lawful use — no cheat devices

The DVSA expects operators to use AdBlue® legitimately to meet emissions standards. Any attempt to disable the SCR system or use an AdBlue® “cheat device” is illegal and will trigger enforcement action, prohibitions, and potential operator-licence consequences.

The Fleet Operator Recognition Scheme (FORS) expects operators to monitor and record their AdBlue® usage — including the diesel-to-AdBlue® ratio — to ensure vehicles meet emissions standards and that SCR systems are being used correctly. There is no single mandatory ratio, as consumption varies by vehicle, but operators must demonstrate that the system is functioning as intended.

Key FORS requirements

1. Monitoring and recording usage

Your organisation must have clear policies and procedures detailing how fuel data — including AdBlue® — is captured, monitored, and reviewed.
If an AdBlue®-to-diesel ratio is not calculated and monitored, auditors will record a minor action during assessment.

2. Operator responsibility

It is the operator’s responsibility to ensure that all AdBlue® and SCR systems work correctly and comply with legislative requirements such as Euro 6 emissions standards.

3. Identifying anomalies

AdBlue® usage data must be monitored regularly to spot unusual patterns.
Sudden increases or decreases may indicate:

• A system fault

• A blocked injector

• Incorrect usage

• Potential tampering

These anomalies must be investigated and resolved promptly.

4. Compliance evidence

Keeping accurate vehicle-by-vehicle records of AdBlue® dispensed provides evidence of correct use. This supports compliance for both FORS audits and DVSA inspections.

5. Documentation and best practice

The FORS Fuel Management Guide outlines recommended processes, data collation methods, and tools to help operators manage fuel and AdBlue usage effectively and meet accreditation standards.

Our free tool provides:

• Instant ratio calculation

• Pass/fail indicators vs expected ranges

• Downloadable audit-ready records

• A simple way to meet FORS & DVSA expectations

No. AdBlue® must never be mixed with diesel.
It must only go into its dedicated AdBlue® tank.

High usage may indicate:

• Faulty NOx sensors

• SCR or injector issues

• Heavy load cycles

• Incorrect or contaminated AdBlue®

If consumption regularly exceeds 10%, a mechanical check is advised.