Science
How does a thermometer work?
A thermometer works by measuring something that changes predictably with temperature. Old liquid thermometers use a fluid that expands as it warms; digital ones use a sensor whose electrical signal shifts with heat.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a thermometer works.
Step by step
- 1Most thermometers track a property that changes with temperature.
- 2Liquid types use a fluid that expands and rises when heated.
- 3Digital types use a sensor whose resistance changes with heat.
- 4The change is converted into a temperature reading.
Frequently asked questions
- How does a thermometer measure temperature?
- It tracks a property — like liquid expansion or electrical resistance — that changes predictably with heat.
- Why does the liquid in a thermometer rise?
- Heat makes the liquid expand, so it climbs the thin tube; cooling makes it contract and fall.
- How do digital thermometers work?
- A heat-sensitive sensor changes its electrical signal, which the device converts into a temperature.