Keeping Your Thermometer Accurate
Learn how often to calibrate your instruments, what equipment you need, and what checkpoints to choose. Keep your instruments accurate, compliant and audit-ready.
Need certified calibration? View our learn more about our calibration services or view our price list.
What is Calibration?
A calibration test compares your thermometer readings with those of a traceable device or reference thermometer. The test is carried out using a known temperature source, such as ice water at 0 °C.
Regular calibration is essential to ensure your thermometers are still reading accurately and to determine whether they need adjusting.
What is a Calibration Certificate?
A calibration certificate shows the results of your calibration test and certifies the instrument’s accuracy.
Obtaining a calibration certificate for your instrument demonstrates to auditors that it is performing correctly.
Traceable Calibration Certificate
Confirms your instrument has been calibrated against recognised standards, with measurements linked through an unbroken chain back to national or international references.
UKAS Calibration Certificate
Issued by a UKAS-accredited laboratory, providing independent, accredited proof that your instrument meets defined accuracy standards. Ideal for audits and quality assurance processes where compliance is essential.
Learn more about how our UKAS-accredited laboratory works.
What Are Calibration Points?
Calibration points are the temperatures at which the thermometer has been calibrated. The number of checkpoints you choose depends on your requirements, and we can complete as many as you need.
Tips for Choosing Calibration Points
More Points, More Confidence
A 5-point certificate is ideal for applications where high accuracy is critical, as it gives confidence across a range of temperatures.
3 Points is a Common Choice
A 3-point certificate is a good amount for a range of applications.
Calibrate at Temperatures You Use
For example, if you use a probe to check refrigerated foods, calibrate at 0 °C, 5 °C and 8 °C.
How Often to Calibrate Your Instruments?
How often you check your thermometer accuracy depends on:
- How often you use your thermometer, and what you use it for.
- How precise you need your thermometer to be.
- Industry standards and compliance requirements.
General advice for industries like food service is to check your thermometers at least once a month. You can do this yourself using calibration equipment such as ice baths.
It’s recommended to send your thermometer to a laboratory for certification every 12 months. Keeping a calibration record is essential for demonstrating compliance with regulatory requirements.
When it’s time for certification, explore our Calibration Services or request a quote.
How to Calibrate a Thermometer
The simplest way to calibrate a thermometer is to use an ice water bath.
- Fill a container to the top with crushed ice.
- Add water until it reaches about ½ inch below the top of the ice.
- Let it sit for a minute. If ice rises from the bottom of the container, remove some water and add more ice.
- Place your thermometer probe tip into the centre of the ice slurry and mix gently.
- Your thermometer should read 0 °C + your thermometer’s specified accuracy.
- For example, a thermometer with an accuracy of ±0.4 °C should read between -0.6 °C and 0.4 °C.
Tip: Using a high-accuracy reference thermometer to compare with the thermometer you’re testing will give additional confidence that you have made your ice bath correctly.
How to Recalibrate Your Thermometer
If your thermometer has fallen outside the instrument’s accuracy range, you should send it to a laboratory for recalibration. They will adjust it so that the accuracy is within the specified range for the instrument, and provide a fresh calibration certificate to prove this has been done.
View our price list to send your instruments to our UKAS laboratory.
Frequently asked questions
How do I calibrate an infrared thermometer?
To calibrate an infrared thermometer, you’ll need a stable temperature source such as a thermometer comparator or black body calibrator to get an accurate reading. Compare the reading on your infrared thermometer with a high-accuracy reference thermometer.
Read our full guide to calibrating an infrared thermometer to learn more.
How do I check the accuracy of a thermometer instrument (without a probe)?
For thermometers with detachable probes, you’ll need to check your instrument accuracy on its own, as well as with a probe.
For this, you can use a temperature simulator or test cap which is compatible with your sensor type:
- Thermocouples — microcal temperature simulator.
- Thermistors — thermistor test caps.
- PT100 units — PT100 test caps.
Shop calibration equipment.
Are there alternatives to ice bath calibration?
Yes. If you need a more accurate way to check your thermometers, you have a large quantity that need testing often, or you want to calibrate your thermometer at different temperatures, there are other options.
- Calibration water bath — checks from 25 °C to 95 °C.
- Dry well heat source calibrator — checks from 33 to 250 °C.
- Dry well cool source calibrator — checks from -10 to 110°C.
How much does professional calibration cost?
Calibration in a laboratory depends on your instrument type and how many checkpoints you require. View our calibration price list to see a breakdown of our costs or to request a quote.
What calibration information do I need for audits?
Calibration requirements are usually set out by your compliance plan (for example, HACCP in food safety).
As a general rule, you should have:
A valid calibration certificate showing traceability to recognised standards.
Records of routine checks, including:
- Date of the check.
- Method used (e.g. ice bath test).
- Results and any deviations.
- Action taken if readings were out of tolerance.
Keeping both the certificate and records of routine checks demonstrates compliance and ongoing control.