A gauge sized purely for "big enough" is usually wrong. ASME B40.100 calls for normal operating pressure to read in the middle third of the dial — legible, and gentle on the Bourdon tube over years of continuous flexing.
Verified against published standard
Service Conditions
If the line can see an occasional upset or surge above normal, enter it — the gauge also has to survive that without its needle burying past full scale.
Enter service conditions and select a range.
About This Calculation
A pressure gauge sized purely to survive the maximum possible pressure, without regard for where NORMAL operating pressure falls on its dial, is a genuinely common specification mistake — ASME B40.100 recommends normal operating pressure read in the middle third (25-75%) of full scale, both for legible needle position and because a Bourdon tube continuously flexed near its full-scale limit wears and fatigues faster than one operating comfortably within its elastic range. This calculator selects an appropriately-sized standard gauge range given normal (and optionally, upset/maximum) operating pressure.
Frequently Asked Questions
Why specifically 25-75% of full scale, not some other range?
Below 25%, the needle sits too close to the pin/stop for precise reading and the gauge is oversized for the actual pressure it’s reading day-to-day; above 75%, the Bourdon tube is continuously flexed close to its elastic limit, accelerating fatigue and reducing calibration life — the middle band balances readability against mechanical longevity.
Why does an occasional upset/surge pressure change the recommended range?
The gauge still needs a genuine safety margin against its OWN overrange limit during any upset, even though normal operation should sit in the 25-75% band — sizing purely for normal pressure could leave an occasional pressure surge pinning the needle past full scale, which can permanently damage the Bourdon tube.
Do all pressure gauges come in the exact standard ranges this calculator checks?
Most manufacturers follow a similar preferred-number sequence for standard ranges, but exact availability varies by vendor and gauge type — always confirm the specific range is actually stocked or manufacturable by your chosen gauge supplier before finalizing a specification.