What's the difference between checking your temperature with a mercury thermometer versus a digital one — which is actually more accurate?

Mercury thermometers have long been considered the gold standard in clinical temperature measurement, and for good reason. They work through a straightforward physical principle: mercury expands as it heats up, rising through a narrow glass tube to indicate temperature. Because this is a direct physical response to heat, mercury thermometers are extremely precise and consistent, typically accurate to within 0.1 degrees Celsius when used correctly. They require no batteries, no calibration over time, and they don't drift the way electronic sensors can. For decades, hospitals and laboratories relied on them precisely because of this reliability. Digital thermometers work differently. They use a thermistor, which is a small electronic component that changes its electrical resistance in response to temperature. A microprocessor then converts that resistance reading into a temperature display. The accuracy of a digital thermometer depends heavily on the quality of the thermistor and the calibration of the device. High-quality digital thermometers can match or even exceed mercury thermometers in accuracy, achieving precision within 0.1 degrees Celsius as well. However, cheaper consumer-grade digital thermometers can be off by 0.2 to 0.5 degrees or more, and their accuracy can degrade over time as the electronic components age or if the device is dropped or exposed to extreme conditions. The practical answer to which is more accurate depends on the specific devices being compared. A well-calibrated, high-quality digital thermometer from a reputable manufacturer is essentially as accurate as a mercury thermometer and may actually be more convenient and faster to use. Digital thermometers typically give a reading in 10 to 30 seconds, while mercury thermometers require holding them in place for 3 to 5 minutes to get a stable reading. If someone removes a mercury thermometer too early, they'll get an inaccurate reading, which is a common user error. Digital thermometers also have audible alerts when they've finished measuring, reducing this kind of mistake. It's worth noting that mercury thermometers are now banned or heavily restricted in many countries and most healthcare settings due to the serious health and environmental hazards mercury poses if the glass breaks. The World Health Organization and many national health agencies have pushed for their phase-out. This has driven significant improvements in digital thermometer technology, and modern clinical-grade digital thermometers used in hospitals are rigorously tested and calibrated to meet strict accuracy standards. Infrared thermometers, which measure temperature from the eardrum or forehead without contact, are also widely used now, though these tend to be slightly less accurate than contact-based digital thermometers and are more sensitive to proper technique. For everyday home use, a decent digital thermometer from a known brand will serve you well and is genuinely accurate enough to detect a fever or monitor illness. If you want to verify your digital thermometer's accuracy, you can compare it against a known reference, such as ice water, which should read 0 degrees Celsius, or boiling water at sea level, which should read 100 degrees Celsius. The bottom line is that mercury thermometers were historically more accurate in practice largely because the technology was mature and consistent, but modern digital thermometers have closed that gap considerably, and the best ones are just as trustworthy while being safer and easier to use.