When measuring temperature, two key concepts determine the reliability of a thermometer: accuracy and precision. While they may seem similar, they describe different aspects of measurement quality. Both are influenced by the device (thermometer) and the probe (sensor).

Accuracy: How Close to the True Temperature?

Accuracy refers to how close a measured temperature is to the true or correct value. A thermometer with high accuracy provides readings that are very near the actual temperature.

For example, at sea level, water boils at 100°C (212°F). If a thermometer gives a reading of 100.1°C, it is highly accurate. However, if another thermometer reads 97°C, it is not accurate.

Several factors affect accuracy, including calibration, the quality and sensitivity of the probe, and external influences such as altitude, air pressure, and probe placement.

Precision: How Consistent Are the Readings?

Precision refers to how repeatable and consistent measurements are when taken multiple times. A thermometer is precise if it gives nearly the same reading every time, even if the reading is not accurate.

For example, measuring boiling water five times with a thermometer and getting 97.5°C, 97.6°C, 97.5°C, 97.6°C, 97.5°C indicates very high precision. However, if the actual boiling temperature should be 100°C, the thermometer is consistently wrong but still precise.

Factors that influence precision include the stability of the thermometer’s electronics, sensor response time and sensitivity, and environmental conditions such as heat fluctuations in boiling water.

Best vs. Worst Case Scenarios

A well-calibrated digital thermometer with a high-quality probe will provide both accuracy and precision. For example, if it consistently reads 100.0°C or 100.1°C for boiling water, it is both accurate and precise.

In contrast, a cheap or unreliable thermometer may give varying readings such as 96°C, 98°C, and 95°C, making it neither accurate nor precise. Even if a thermometer is precise, such as always reading 97.5°C, it is still incorrect if the expected value is 100°C.

How to Ensure Both Accuracy & Precision

To achieve accurate and precise temperature readings, use well-calibrated thermometers with reliable sensors. Reference points such as ice water (0°C) and boiling water (100°C at sea level) help verify accuracy. Avoid touching metal surfaces with the probe, as this can affect readings. Consistency in probe placement and stable environmental conditions further enhance measurement reliability.

Both accuracy and precision are critical in temperature measurement, but they serve different purposes. A thermometer should ideally have both to provide reliable and repeatable readings in scientific, industrial, and culinary applications.