水银温度计由玻璃制成包含水银球及水银柱的温度计。末端水银球随测量位有不同形状和大小，如口表呈细长型、肛表则为短而圆或用颜色加以区别。体温计之水银受热膨胀。水银柱升高的度数依受热程度而定，上升到相当刻度后不再上升之数据即为正确的体温读数（每度分成10小格，每格为1/10度）。水银柱与水银球连接的上端轻微狭窄，防止水银倒流至球中，体温表使用后水银柱不会自动下降，须快速的甩动水银才会下降至球内，自动下降的体温表必须丢弃。水银柱的直径约1/1000至2/1000吋，体温表的一面是平的使刻度清楚易读，避免从桌面或平滑表面摔破。刻度范围是摄氏34度至42.2度。（本段文本主要描述「水银体温计」、并非描述「水银温度计」。而「水银温度计」可量度的温度介于-38℃和357℃之间。）

The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen or it may be at less than atmospheric pressure, a partial vacuum.