Calculate pressure from manometer height difference for U-tube, differential, inclined, and well-type manometers with multiple manometer fluids.
A manometer is one of the oldest and most reliable pressure-measuring devices. It uses the height difference of a liquid column to determine pressure: ΔP = ρgΔh. Despite the advent of electronic transducers, manometers remain in use for calibration, laboratory work, and HVAC system balancing because of their inherent accuracy and simplicity.
This calculator supports four manometer configurations: simple U-tube (one side open to atmosphere), differential U-tube (connected between two pressure taps), inclined-tube (for increased sensitivity at low pressures), and well-type (reservoir). You select a manometer fluid — mercury, water, oil, alcohol, or custom — enter the height difference, and get the pressure in six unit systems.
The inclined-tube mode is particularly useful for HVAC and clean-room applications where pressure differences are small (< 250 Pa). By tilting the tube, the liquid travels further along the tube for the same vertical height, amplifying the reading by a factor of 1/sin(θ).
Use this calculator when you need to turn a column-height reading into engineering pressure units without manually switching between fluid densities and manometer types.
It is useful for lab measurements, HVAC balancing, calibration work, and quick checks of low differential pressures where manometers are still more transparent than electronic sensors.
Simple U-tube: ΔP = ρ_m × g × Δh Differential: ΔP = (ρ_m − ρ_f) × g × Δh Inclined: ΔP = ρ_m × g × L × sin(θ) Where: • ρ_m = manometer fluid density (kg/m³) • ρ_f = pipe fluid density (kg/m³) • g = 9.81 m/s², Δh = height difference (m) • L = tube reading (m), θ = inclination angle
Result: ΔP ≈ 19.93 kPa (149.6 mmHg)
ΔP = 13 546 × 9.81 × 0.15 = 19 934 Pa ≈ 19.93 kPa. This is equivalent to about 150 mmHg or 2.89 psi.
Manometers work well because the measurement is directly tied to hydrostatics. That makes them valuable for calibration and low-pressure work where you want a traceable, visually obvious reading rather than a black-box sensor output. They are especially useful when a small differential pressure still has to be trusted without relying on an electronic sensor calibration chain.
Most errors come from using the wrong fluid density, confusing vertical height with along-tube length in an inclined setup, or forgetting whether the reading is gauge, differential, or absolute pressure. For precision work, temperature correction and clean meniscus reading technique matter more than the arithmetic.
Mercury's high density (13 546 kg/m³) means a moderate pressure creates a manageable column height. For 1 atm, only 760 mm of mercury is needed vs 10.3 m of water.
For low pressures (< 250 Pa or 1 inH₂O). The inclined tube amplifies the reading — at 30°, tube travel is 2× the vertical height, doubling the resolution.
A U-tube manometer with one end open to atmosphere measures gauge pressure (relative to atmospheric). For absolute pressure, add atmospheric pressure to the reading.
A well-made mercury manometer can achieve ±0.1 mmHg (≈ ±13 Pa). Inclined manometers with coloured oil can resolve about ±0.5 Pa in controlled conditions.
Yes, water manometers are common for low-pressure HVAC work. However, water is 13.6× less dense than mercury, so column heights are much taller for the same pressure.
One side of the U-tube is replaced by a large reservoir. The liquid level in the reservoir barely changes, so you only need to read one tube. Accuracy is slightly reduced by the finite reservoir correction.