Which tool is commonly used to measure mass?

The pan balance is an instrument designed specifically for measuring mass. It operates by balancing an object of unknown mass against a known mass, allowing for an accurate measurement of the object's mass in grams or kilograms. The principle behind a pan balance is based on equilibrium; when the weights on both sides are equal, it indicates that the mass of the object being measured matches that of the calibrated weights.

In contrast, the other tools listed serve different purposes. A beaker is typically used for measuring volume, often containing liquids. A graduated cylinder is also meant for measuring liquid volume more accurately than a beaker. A thermometer is specifically used to measure temperature. Since mass measurement requires a balance of forces, the pan balance is the appropriate choice for this task.