Manometer Calculator (U-Tube & Inclined Manometer)
By Santaji GadepatilinUpdated November 5, 2026
A manometer measures pressure difference as the height of a liquid column, and tilting the tube spreads a small height over a longer, easier-to-read scale. This manometer calculator converts a U-tube or inclined manometer reading into pressure, including the effect of the fluid above the manometer liquid — see the U-tube manometer working principle and formula.
How to use the manometer calculator
Enter the manometer liquid density, the density of the fluid above it (air ≈ 1.2 kg/m³, or the process liquid), the reading along the tube and the tube angle — 90° for a vertical U-tube. The calculator returns the vertical height and the differential pressure.
Manometer formula
h = L × sin θ · Δp = (ρm − ρf) × g × h
Worked example
A water-filled inclined manometer at 30° reads 150 mm along the tube, measuring air:
- h = 150 × sin 30° = 75 mm
- Δp = (1,000 − 1.2) × 9.80665 × 0.075 = 734.6 Pa
Pressure for a 100 mm scale reading (Pa, measuring air)
| Manometer liquid | Vertical (90°) | Inclined 30° | Inclined 10° |
|---|---|---|---|
| Water | 979.5 | 489.7 | 170.1 |
| Red gauge oil (SG 0.826) | 808.9 | 404.4 | 140.5 |
| Paraffin (SG 0.80) | 783.4 | 391.7 | 136.0 |
| Mercury | 13331.0 | 6665.5 | 2314.9 |
Notes
- For a liquid-over-liquid manometer (for example mercury under water) the fluid density term matters: use ρm − ρf.
- Level the instrument carefully — an error of 1° at a 10° incline changes the reading by about 10%.
Frequently asked questions
What is the U-tube manometer formula?
Δp = (ρm − ρf) × g × h, where ρm is the manometer liquid density, ρf the density of the fluid above it and h the difference in liquid levels. For gases ρf is usually negligible.
How does an inclined manometer work?
The vertical height is h = L × sin θ, so at 30° the scale reading L is twice the vertical height; at about 5.7° it is ten times. This makes small pressures easier to read.
What fluid should I use in a manometer?
Water or light gauge oil for small draft and filter pressures (a few hundred Pa), mercury for pressures of tens of kPa. Mercury is now avoided for safety reasons.
What is 1 mm of water column in pascals?
About 9.81 Pa (9.80665 Pa by definition at standard gravity).