Manometer Calculator
Free calculate pressure difference from fluid height using δp = ρgh. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
Mercury: ~13,600 kg/m³, Water: ~1,000 kg/m³
Difference between fluid column heights
Standard: 9.81 m/s² on Earth
Results
Enter parameters to calculate
What is a Manometer?
A manometer is a device used to measure pressure differences by comparing the heights of fluid columns. The most common type is the U-tube manometer, which consists of a U-shaped tube partially filled with a liquid (often mercury or water).
When there's a pressure difference between the two sides of the manometer, the fluid level rises on one side and falls on the other. The height difference between the two columns is directly related to the pressure difference through the hydrostatic pressure equation.
Manometers are widely used in laboratories, HVAC systems, and industrial applications to measure pressure differences, gauge pressures, and vacuum levels. They're simple, reliable, and don't require calibration like electronic pressure sensors.
Manometer Formula
Where:
- • ΔP = Pressure difference (Pa)
- • ρ = Fluid density (kg/m³)
- • g = Acceleration due to gravity (m/s²)
- • h = Height difference between fluid columns (m)
Common conversions:
1 Pa = 1 N/m², 1 kPa = 1000 Pa, 1 bar = 100,000 Pa
1 mmHg (torr) = 133.322 Pa, 1 inHg = 3,386.39 Pa
How to Calculate
-
1
Measure height difference
Measure the vertical distance (h) between the two fluid column levels in the U-tube.
-
2
Convert units to SI
Convert height to meters, ensure density is in kg/m³, and gravity in m/s².
-
3
Calculate pressure difference
Apply ΔP = ρgh. Multiply density, gravity, and height difference.
-
4
Convert to desired units
Convert the result to kPa, bar, PSI, mmHg, or other pressure units as needed.
Practical Examples
Example 1: Mercury Manometer
Mercury (ρ = 13,600 kg/m³), h = 0.2 m, g = 9.81 m/s².
Solution:
ΔP = 13,600 × 9.81 × 0.2
ΔP = 26,683.2 Pa ≈ 26.68 kPa
ΔP ≈ 200 mmHg (torr)
Example 2: Water Manometer
Water (ρ = 1,000 kg/m³), h = 0.5 m.
Solution:
ΔP = 1,000 × 9.81 × 0.5
ΔP = 4,905 Pa ≈ 4.9 kPa
Applications
Laboratory
Measuring pressure differences in experiments, calibrating instruments, and monitoring vacuum systems.
HVAC Systems
Measuring air pressure differences in ventilation systems, ductwork, and air handling units.
Industrial
Monitoring pressure in pipelines, tanks, and process equipment. Simple and reliable for many applications.
Education
Teaching hydrostatics, pressure measurement, and demonstrating fluid mechanics principles.
Frequently Asked Questions
Why use mercury in manometers?
Mercury's high density (13,600 kg/m³) means smaller height differences for the same pressure. A 0.1 m mercury column ≈ 1.36 m water column. Mercury is also non-wetting and doesn't evaporate easily.
What if the manometer is inclined?
For an inclined manometer, use the vertical height difference, not the length along the tube. h = L × sin(θ), where L is the length along the tube and θ is the angle from horizontal.
How do I measure gauge pressure?
If one side is open to atmosphere, the height difference gives gauge pressure (pressure relative to atmospheric). Absolute pressure = gauge pressure + atmospheric pressure.
What about temperature effects?
Temperature affects fluid density. For accurate measurements, use density at the actual temperature, or apply temperature corrections. Mercury expands with temperature, reducing density slightly.
Can I use different fluids?
Yes! Water, oil, alcohol, and other liquids can be used. Choose based on density (affects sensitivity), viscosity (affects response time), and compatibility with measured fluid.