Accuracy and calibration of food thermometers

A thermometer that is off by several degrees can make a safe food appear unsafe or, more seriously, make food appear adequately cooked or held when it is not. Food managers need the right device, an accuracy check, and a probe suited to the product being measured.

Accuracy requirement and device choice

The 2026 FDA Food Code applies its accuracy requirement to food temperature measuring devices generally: ±1°C for Celsius or dual-scale instruments and ±2°F for Fahrenheit-only instruments, within the intended range of use. The model also requires suitable devices to be readily accessible and a small-diameter probe for thin foods such as patties and fish fillets. A device’s display resolution is not the same as its accuracy: showing tenths of a degree does not prove the measurement is correct. Check that the thermometer is designed for the temperatures and foods where employees will use it, and follow the jurisdiction’s adopted code.

Calibrate before relying on a reading

Common reference checks use an ice-water slurry or boiling water, but the correct method depends on the thermometer’s design and manufacturer instructions. An ice-point check should use a well-mixed slurry of ice and water, with the sensing area immersed without touching the container. Water boils at a temperature that changes with altitude, so a boiling-point check must use the expected local value or an approved reference. Some digital devices allow adjustment; others require calibration by the manufacturer or removal from service. Record the result if the establishment’s procedure requires a calibration log.

Place the probe correctly

For a bimetallic stem thermometer, the sensing area is along the stem, not just at the tip; immerse it to the marked sensing zone and avoid touching the pan or bone. A thin food may require a smaller-diameter probe to measure accurately. Allow the reading to stabilize and measure the coldest or thickest portion when checking cooking or holding temperature, as the procedure requires.

Keep calibration separate from cleaning

Calibration addresses measurement accuracy; cleaning and sanitizing prevent contamination. A thermometer can be accurately calibrated and still transfer pathogens or allergens if the probe is not cleaned between foods. Maintain both controls and record checks when the facility procedure or regulator requires it.

Key takeaway

Choose a suitable thermometer, verify its accuracy, calibrate it as directed, and use the sensing area correctly. Accuracy and sanitation are separate controls that both support safe food decisions.

Choose the probe for the product

The sensing zone and probe size determine whether a reading represents the food. A bimetallic stem thermometer senses along an area of the stem, so it needs enough depth to immerse that zone. In a thin patty or filet, the stem may not fit without touching the pan or passing through the food. A small-diameter thermocouple or thermistor probe is designed for these thin masses. For a large roast or dense casserole, place the probe in the thickest portion and avoid bone, fat pockets, container walls, or other surfaces that could distort the result. Follow the cooking or holding procedure for the exact location and number of readings.

Treat calibration, sanitation, and corrective action separately

Calibration checks whether the instrument measures accurately; cleaning and sanitizing protect food from contamination. Clean and sanitize a probe between foods and after any contact that could transfer pathogens or allergens. If a device is damaged, gives inconsistent readings, or falls outside its accuracy specification, stop relying on it and adjust or replace it according to the manufacturer’s directions. Recheck the affected food with a working thermometer and take the appropriate holding, cooking, or discard action under the facility procedure. A calibration record supports the process, but it cannot make an inaccurate reading safe.

Use a simple verification routine

A practical routine names the devices employees may use, identifies which probe fits each food, specifies when to check calibration, and explains what to do when a thermometer fails. Train employees to wait for a stable reading and to check the food rather than relying only on the refrigerator or hot-holding unit display. A manager can compare readings from a reference check, inspect probes for damage, and review temperature logs for patterns that suggest drift. The frequency and method should follow manufacturer specifications, the adopted code, and the establishment’s written procedure rather than an arbitrary daily rule.

Set up an ice-point check correctly

When the manufacturer allows an ice-point check, use a clean container filled with crushed ice and enough clean water to fill the spaces. Stir the mixture, place the sensing area in the slurry, and keep it away from the container’s sides and bottom. Wait for the display to stabilize and compare it with the reference temperature specified by the manufacturer. Add or remove ice as needed to keep a dense slurry rather than a cup of mostly water. If the device cannot be adjusted to specification, mark it out of service and use a verified replacement. Do not use a single reference check to assume accuracy across every temperature in the instrument’s range unless the manufacturer’s procedure supports that conclusion.

A boiling-water check is another possible reference, but it is sensitive to elevation and local conditions. Water boils below 212°F at higher elevations, so comparing the thermometer with 212°F everywhere can create a false failure or false pass. Use a reliable local reference value and the thermometer’s intended range. If the device is meant only for refrigeration temperatures, a boiling check may be outside its specified range and may not verify its useful performance. The goal is a valid check over the temperatures where the establishment relies on the instrument.

Respond when a check fails

If a thermometer fails its reference check, do not quietly record a correction and continue using it unless the manufacturer’s process permits an adjustment and a second check confirms the result. Identify the device, adjust or replace it, and verify that the replacement meets specification. Review foods measured since the last acceptable check when the error could have affected a critical decision. Recheck current products with a reliable instrument and apply the establishment’s corrective-action procedure. This sequence connects calibration to food control: a log records what happened, while a reliable measurement supports the actual safety decision.