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What Is a Pressure Gauge? How It Works, Types and Uses
Quick answer: a pressure gauge is an instrument that shows the pressure of a gas or liquid on a dial or a digital display. The most common type, the Bourdon tube gauge, uses a curved metal tube that straightens slightly under pressure and moves a pointer. Pressure is force divided by area, and it is measured in units such as kPa, bar and psi. Gauges are used on pumps, compressors, boilers, hydraulic systems and gas lines to check that equipment is working safely and efficiently. This guide is the starting point for beginners: it explains what a gauge does, how it works, the main types, how to read one, and where to go next.
What does a pressure gauge do?
Pressure is the force a fluid exerts on a surface, per unit area. You cannot see it, but you need to know it. Too little pressure and a pump or tool will not work properly. Too much, and pipes, vessels and hoses can burst. A pressure gauge makes pressure visible so that a person can check it quickly.
The idea is simple: pressure = force ÷ area. If a force of 1,000 newtons pushes on 0.01 square metres, the pressure is 100,000 pascals, which is 100 kPa or 1 bar. That is roughly the weight of a 100 kg mass spread over a 10 cm by 10 cm square.
Pressure units explained
| Unit | Equals | Where you see it |
|---|---|---|
| Pascal (Pa) | 1 newton per square metre | Very low pressures, standards |
| Kilopascal (kPa) | 1,000 Pa | Australian industry and gas work |
| Megapascal (MPa) | 1,000,000 Pa = 10 bar | High pressure and hydraulics |
| Bar | 100 kPa, about atmospheric pressure | Europe and general industry |
| psi | 6.895 kPa; 14.5 psi = 1 bar | United States equipment, tyres |
Many Australian gauges carry a dual scale, with kPa in black and psi in red, so you can read either. Digital gauges let you switch units with a button.
How a Bourdon tube gauge works
- Pressure enters the gauge through the connection at the base.
- It flows into a curved, flattened metal tube sealed at one end.
- The pressure tries to straighten the tube, so its free end moves a small distance.
- A link and a geared sector magnify that movement and turn a pointer.
- The pointer shows the pressure on a printed scale.
When the pressure falls, the tube springs back and the pointer returns to zero. No power is needed. For more depth, read Bourdon tube pressure gauges explained.
Main types of pressure gauge
| Type | How it senses | Typical use |
|---|---|---|
| Bourdon tube | Curved tube straightens | General industrial pressure from low to very high |
| Capsule | Two thin diaphragms flex | Very low pressure air and gas |
| Diaphragm | A thin membrane flexes | Corrosive, sticky or hygienic media |
| Liquid filled | Bourdon in a filled case | Vibrating and pulsating lines |
| Digital | Electronic sensor and display | Testing, accuracy, logging |
| Differential | Compares two pressures | Filters, flow, level |
Examples from our range include the L100 liquid filled gauge, the KPCh capsule gauge and the PDK PDR250 digital gauge.
Parts of a gauge
- Case: protects the movement. Stainless steel, steel or plastic.
- Window: glass, acrylic or polycarbonate. Safety glass is used where fragments could cause injury.
- Dial and pointer: the scale and the needle.
- Movement: the gear mechanism between the tube and the pointer.
- Bourdon tube or element: the part that senses the pressure.
- Socket and connection: the threaded fitting that attaches to the system. See connection types and thread sizes.
- Fill (optional): glycerine or silicone oil that damps vibration.
How to read a pressure gauge
- Look at the dial straight on to avoid parallax error.
- Find the units printed on the dial. Check whether there is a second scale.
- Read where the pointer sits against the scale. Note the graduations: each small mark may be 1, 2 or 5 units.
- Check that the pointer rests at zero when there is no pressure.
- Read the pressure and write it down with the units.
Example. The dial shows 0 to 1,000 kPa with marks every 20 kPa. The pointer is halfway between the 600 and 700 marks. That is about 650 kPa, or 6.5 bar, or about 94 psi.
Gauge pressure, absolute pressure and vacuum
Most gauges show gauge pressure, which is pressure above the atmosphere. Absolute pressure counts from a perfect vacuum. Vacuum is pressure below the atmosphere. A tyre gauge reading 220 kPa is showing gauge pressure; the absolute pressure is about 321 kPa. For the full picture, see gauge vs absolute vs vacuum pressure explained and vacuum gauges.
Where are pressure gauges used?
- Pumps and water supply: checking discharge and suction pressure.
- Compressed air: monitoring receivers and regulators. See pressure gauges for air compressors.
- Hydraulics: setting relief valves and checking pumps. See hydraulic pressure gauges.
- Boilers and steam: monitoring safe operating pressure. See steam and boiler gauges.
- Gas: checking regulators and low pressure supplies. See gas and LPG gauges.
- Food and process plants: monitoring tanks and lines.
How to choose a gauge: six quick questions
- What is the normal and maximum pressure? Choose the range with headroom. See the range selection guide.
- What fluid or gas? That sets the material.
- Is there vibration or pulsation? Consider a liquid filled gauge. See liquid filled vs dry.
- How accurate must it be? See pressure gauge accuracy compared.
- Analogue or digital? See analogue vs digital pressure gauges.
- Does a control system need the pressure? Then you want a sensor or transmitter. See transducer vs transmitter vs sensor.
Safety basics
- Never exceed the gauge range.
- Release pressure before removing a gauge.
- Use a gauge with a blowout back or safety glass on high pressure or hazardous duty.
- Do not use a gauge on oxygen unless it is cleaned and rated for it.
- Replace gauges that have a bent pointer, a cracked window or leaks.
A short history
The Bourdon tube gauge was patented in 1849 by the French engineer Eugene Bourdon, and the basic idea has barely changed since. The reason is simple: a curved metal tube that straightens under pressure is a reliable, cheap and power-free way to move a pointer. Digital gauges are far newer, but they have not replaced the mechanical gauge, because each has jobs it does better.
Common sizes
| Dial size | Typical use |
|---|---|
| 40 to 50 mm | Small compressors, regulators and equipment panels |
| 63 mm | Compact industrial panels, pumps and test points |
| 100 mm | The standard industrial size for plant and pipework |
| 150 to 160 mm | Boilers and process plants, where operators read from a distance |
Common problems and what they mean
| What you see | Likely meaning |
|---|---|
| Pointer fluttering | Vibration or pulsation; consider a liquid filled gauge or a snubber |
| Pointer rests above or below zero | The tube was overpressured or the pointer has slipped; replace the gauge |
| Pointer sticks | Blocked port, dirt or damaged movement |
| Fogged or cloudy dial | Moisture in a dry case or a leaking seal |
| Reading differs from another gauge | Calibration drift or different accuracy classes; check both against a reference |
A mini glossary
- Range: the lowest to highest pressure the dial shows.
- Span: the difference between the top and bottom of the range.
- Accuracy class: the allowed error as a percentage of span. See accuracy compared.
- Over-range protection: how much above full scale the gauge can withstand.
- Dry and liquid filled: whether the case holds air or a damping liquid.
Five things to check on an unknown gauge
- The range and units printed on the dial.
- The accuracy class, if marked, and the dial size.
- The connection thread and position (lower or back mount).
- Whether the case is dry or liquid filled.
- That the pointer rests at zero with no pressure applied.
Do and do not
- Do fit an isolation valve so you can remove the gauge safely.
- Do read the dial straight on.
- Do not exceed the range, even briefly.
- Do not tighten the gauge by its case. Use a spanner on the socket flats.
- Do not use a general gauge on oxygen.
Gauge or sensor in one line
A gauge shows pressure to a person at the machine. A sensor sends pressure to a machine or a control system. Many installations use both. See the sensor, transducer and transmitter guide.
Why accuracy class matters
Every gauge has an accuracy class that sets how far it may be wrong. A class 2.5 gauge on a 0 to 1,000 kPa range may be out by 25 kPa, while a class 1.0 gauge may be out by 10 kPa. For a quick check that is fine. For setting a valve or verifying a limit, choose a better class. Read accuracy compared in real numbers for examples.
Standards note (checked 5 November 2026)
AS 1349 is the Australian standard for Bourdon tube pressure and vacuum gauges. The current edition is AS 1349-1986, reconfirmed in 2018. It covers gauges with circular concentric scales in the range -100 kPa to +100,000 kPa and nominal sizes from 50 mm to 300 mm. EN 837-1 is the equivalent European standard. Check which one your site or contract names.
Frequently asked questions
What is a pressure gauge used for?
To show the pressure in a pipe, tank, pump or machine, so that operators can check that it is safe and within normal limits.
How accurate is a pressure gauge?
General gauges are accurate to 1% to 2.5% of full scale. Precision digital gauges reach 0.025% to 0.5%.
What does a pressure gauge measure in?
Commonly kPa, bar or psi. The dial shows the unit.
Why are some gauges filled with liquid?
To steady the pointer and protect the movement from vibration.
How often should a gauge be calibrated?
Often once a year, but it depends on use. See pressure gauge calibration.
Your next steps
Browse the pressure gauges category and the digital pressure gauges, or contact us with your application. For the full set of guides, see the digital pressure gauge buying guide.
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