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General information on measuring devices, not medical advice. Follow the instructions for use (IFU) that came with your thermometer.
Short answer: you can check many contact thermometers yourself with a single-point ice-point check, but that is a check, not a traceable calibration. A thermometer that must be trustworthy for records (for example vaccine storage) needs a calibration certificate from a testing provider, and an infrared thermometer is not something you adjust at home.
This page is for anyone who owns a digital, dial or infrared thermometer and needs to decide whether to check it themselves, send it out, or replace it. Related background: thermometer accuracy, what calibration is and types of medical thermometer.
What you need
- The thermometer’s IFU, to find out whether the maker allows user adjustment at all.
- Pure ice and clean water, so that solid and liquid coexist in one container (Fluke Calibration, ice point method).
- A container that holds the mixture and lets the probe tip sit in it without touching the sides or bottom.
- For records that others rely on: a calibration certificate from a testing provider (see below).
How to calibrate a thermometer: the ice-point check
The ice-point method compares the thermometer with 0 °C, the temperature of a mixture of pure ice and water in which solid and liquid coexist. Steps as described by Fluke Calibration:
- Prepare a mixture of pure ice and water so that both solid ice and liquid water are present.
- Submerge the probe tip in the mixture without letting it touch the sides or bottom of the container.
- Wait for the reading to stabilise.
- Compare the stable reading with 0 °C.
- If the difference is not acceptable, adjust the thermometer where its design allows, otherwise treat it as out of tolerance (see below).
What this does and does not tell you, per the same Fluke article: it checks one point only. Being right at 0 °C does not guarantee accuracy at higher temperatures, and detecting drift across a range needs a multi-point check. Ice baths can carry uncertainties of up to a few tenths of a degree Celsius, and Fluke states an ice bath by itself does not meet the criteria for ISO 17025 or ITS-90 traceability.
How to calibrate a digital thermometer
Run the ice-point check above, then follow the IFU for any adjustment or offset the model allows. If the IFU offers no user adjustment, the only options are to accept the result, send the unit for calibration testing, or replace it. Battery changes may warrant checking the device against a known, calibrated thermometer (CDC Vaccine Storage and Handling Toolkit).
How to calibrate an infrared thermometer
Do not improvise an adjustment. An infrared thermometer does not read a probe immersed in an ice bath, so the ice-point steps above do not apply to it. Use the procedure and any verification or return-to-maker route in the manufacturer’s IFU, and contact the manufacturer if the unit appears out of specification. For usage, see how to use an infrared thermometer. Note that the CDC does not recommend infrared thermometers for vaccine storage temperature monitoring.
What can go wrong
- Impure ice or water. Trace impurities lower the freezing point of the mixture (Fluke).
- Wrong ice-to-water ratio or large ice pieces destabilise the equilibrium (Fluke).
- Pressure and container. Changes in atmospheric pressure and a poorly insulated container affect the result (Fluke).
- Assuming one point proves everything. A pass at 0 °C says nothing about other temperatures.
- Dropped or damaged device. The CDC says a dropped, hit or potentially damaged thermometer should have its accuracy checked against another calibrated device, and if there is any question, be replaced or sent for calibration testing.
When to get professional help: certificates and replacement
The CDC toolkit says calibration testing should be done every 2 to 3 years or per the manufacturer’s recommended schedule, and applies to vaccine storage monitoring devices. Outside that setting, check your own program’s rules; see calibration interval.
What a calibration certificate should show
The CDC toolkit lists the following indicators (one or more) that a certificate is acceptable: conformity to ISO/IEC 17025; work by a laboratory accredited by an ILAC Mutual Recognition Arrangement signatory body; traceability to NIST standards; ASTM E2877 Tolerance Class F or higher; or another acceptable accuracy validation method, such as comparison to other traceable reference standards or tests at thermometric fixed points. Each certificate should include:
| Field | What the CDC toolkit says |
|---|---|
| Model | Device name or number |
| Serial number | Included on the certificate |
| Date of calibration | Included on the certificate |
| Uncertainty | Recommended uncertainty of ±0.5 °C (±1 °F) or less |
| Result | Confirmation the instrument passed or is in tolerance (some vendors certify only passing units and may not state “passed”; keep the vendor’s statement on file) |
More on reading these documents: ISO 17025 calibration certificate interpretation.
After a failed check
For vaccine storage, the CDC states that if calibration testing shows a device is not accurate within ±0.5 °C (±1 °F), it must be replaced. That limit comes from the vaccine-storage context and should not be assumed to apply to a clinical thermometer. The CDC does not recommend the following for vaccine storage monitoring: alcohol or mercury thermometers, bimetal stem thermometers, food thermometers, chart recorders, infrared thermometers, and any device without a current, valid Certificate of Calibration Testing. Medical supplies for temperature monitoring are listed in the diagnostic, monitoring and imaging category.
FAQ
How often should a thermometer be calibrated?
For vaccine storage monitoring devices, the CDC says every 2 to 3 years or according to the manufacturer’s recommended schedule. For other uses, follow the IFU or your program’s rule.
Can I calibrate a thermometer with ice water?
You can perform an ice-point check at 0 °C, which tests one point only. It is not a traceable calibration, according to Fluke Calibration.
Can I calibrate an infrared thermometer myself?
Only as far as the manufacturer’s IFU allows. The ice-bath method is for immersion probes, so use the maker’s procedure or support.
What if the thermometer fails the check?
Adjust it only if the IFU permits, otherwise send it for calibration testing or replace it. In vaccine storage, a device outside ±0.5 °C (±1 °F) must be replaced.
Sources
- CDC, Vaccine Storage and Handling Toolkit (PDF): cdc.gov/vaccines/hcp/downloads/storage-handling-toolkit.pdf, checked 2026-11-03.
- Fluke Calibration, Ice Point Method Calibration: Overview, Use Cases, Challenges: fluke.com, checked 2026-11-03.
