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Smelting point, or melting point, is the temperature at which a solid substance changes into a liquid. For a pure crystalline substance at standard atmospheric pressure, the melting occurs at a single well-defined temperature. If a material contains impurities, melting typically happens over a range of temperatures rather than at one point, and the observed melting may begin at a lower temperature than the end of melting.

The melting point is influenced by pressure. For most substances, the melting temperature tends to rise with increasing pressure. Water is a common exception: ice melts at lower temperatures under higher pressure because solid water (ice) is less dense than liquid water, giving a negative slope in the melting curve.

Measurement and detection methods vary. The simple capillary method involves heating or cooling a small sample sealed in a capillary tube while observing the temperature at which melting begins and completes. More advanced techniques include differential scanning calorimetry (DSC) and differential thermal analysis (DTA), which monitor heat flow or temperature changes during melting. Pure substances exhibit a sharp melting point, whereas mixtures or impure samples display a melting point range.

Applications of melting point data include identity verification and purity assessment in chemistry, materials science, and pharmaceuticals, as well as process design for melting, casting, and alloy formation. In mixtures, a eutectic composition may melt at a single, lower temperature than its constituents, while other compositions melt over a broader range. Understanding melting points helps predict material behavior during heating and informs quality control and formulation decisions.