Vacuum is measured with different gauge types for different pressure ranges: mechanical (Bourdon/piezo) gauges for rough vacuum, Pirani/thermocouple gauges for medium vacuum, capacitance (capacitance manometer) gauges for accurate absolute readings, and Penning/hot-cathode ion gauges for high and ultra-high vacuum. No single gauge covers the whole range.
Match the gauge to the range
| Gauge type | Range | Notes |
|---|---|---|
| Mechanical (Bourdon, piezo) | Atmosphere to ~1 mbar | Simple, robust, gas-independent |
| Pirani / thermocouple | ~1000 to 10-3 mbar | Thermal conductivity; gas-dependent |
| Capacitance manometer | Wide, very accurate | Absolute, gas-independent |
| Penning / hot-cathode ion | 10-3 to 10-10 mbar | For high and ultra-high vacuum |
Why gas type matters
Thermal (Pirani) and ionisation gauges read differently for different gases, so a reading may need a correction factor. Capacitance manometers measure true pressure regardless of gas.
Reading the units
Gauges may read in mbar, Torr or microns. A faulty or wrong-range gauge is a common reason a pump seems not to reach vacuum – see troubleshooting.
Need a vacuum gauge or a system specified?
Tell us your vacuum range and we’ll recommend the right gauge and pump. Email [email protected] or request a quote.
Frequently asked questions
How is vacuum measured?
With a vacuum gauge suited to the pressure range: mechanical gauges for rough vacuum, Pirani or thermocouple gauges for medium vacuum, capacitance manometers for accurate absolute readings, and Penning or ion gauges for high and ultra-high vacuum.
Why do two vacuum gauges read differently?
Thermal (Pirani) and ionisation gauges are gas-dependent, so they read differently for different gases and may need correction factors. Capacitance manometers read true pressure regardless of gas.
Which vacuum gauge do I need?
Choose by your pressure range: Pirani for medium vacuum, capacitance manometer for accurate absolute measurement, and Penning or ion gauges for high and ultra-high vacuum.
Written by the Girovac technical team. Girovac Ltd has supplied and serviced industrial and laboratory vacuum equipment from its North Walsham workshop since 1983. Last updated: July 2026.