In level measurement, pressure is equal to the product of height and what property?

• A. Surface tension
• B. Temperature
• C. Viscosity
• D. Specific gravity

Answer: (D)

In a static liquid, pressure at a depth comes from the weight of the liquid above it, which is described by p = ρ g h. Here, the density ρ (how much mass is in a given volume) sets how much pressure a given height h generates. In level measurement, this density is often expressed as specific gravity, a ratio to water, so ρ can be written as SG × ρ_water. That makes the pressure proportional to height times the liquid’s density (via SG). Surface tension, temperature, and viscosity don’t directly determine hydrostatic pressure in a column—the height and the fluid’s density govern it. So the property that multiplies height to give pressure is the specific gravity.