Pressure gauge: types, accuracy grades and calibration standards

Pressure gauge calibration compares a gauge’s readings with a more accurate, traceable pressure reference, a deadweight tester or a calibrated reference gauge on a comparator, at several points across its range, first with pressure rising and then falling, and records the deviation and its uncertainty at each point (DKD-R 6-1, §3 and §7; VIM 2.39). Resetting the pointer to zero is an adjustment, not a calibration (VIM 3.11), and a gauge that reads zero correctly can still be off at mid-scale.

This page is the overview. For the checks you can do yourself, deadweight tester vs comparator, test points, hysteresis and a worked example, see pressure gauge calibration step by step.

Types of pressure gauges

Type	What to know for calibration
Bourdon tube dial gauge	The most common; rated by accuracy grade or class as a percentage of span. DKD’s recommended interval depends on the class (DKD-R 6-1, App. F)
Electronic (digital) gauges and transmitters	Calibrated the same way; need their warm-up time. Also used as references, but less stable over time than a deadweight tester (DKD-R 6-1, §3 and App. F)
Compound and vacuum gauges	Need test points below zero: at least two when calibrated on both sides of zero (DKD-R 6-1, Table 1, notes)
Absolute gauges (including barometers)	Do not read zero at atmospheric pressure, so a zero check does not apply; they need an absolute reference (DKD-R 6-1, §8.6.2)
Low-pressure differential gauges (Magnehelic)	Read inches of water; most ranges ±2 % of full scale (Dwyer, Series 2000 data sheet). Mounting position matters

Accuracy grades and classes

In the US, dial gauges are graded to ASME B40.100; in Europe, to EN 837-1 classes. In both, the percentage is of the span, not of the reading. ASME B40.100 (2022) is a paid standard; each grade below is confirmed by at least two of these manufacturer and distributor sources (Ashcroft; WIKA data sheets; Boshart). Lower grades also exist; check your data sheet:

ASME B40.100 grade	Permissible error, % of span
4A	±0.1 %
3A	±0.25 %
2A	±0.5 %
1A	±1 %
A	±2 % in the first and last quarters, ±1 % in the middle half
B	±3 % in the first and last quarters, ±2 % in the middle half

EN 837-1 classes work the same way: a class 1.0 gauge is good to ±1 % of span, class 0.6 to ±0.6 % (WIKA data sheets; DKD-R 6-1, App. B, E and F).

Standards and guides that apply

Document	Scope	Access
DKD-R 6-1 (2014, rev. 3)	Calibration of pressure gauges: references, sequences, points, uncertainty, certificate, recommended intervals	Free
EURAMET cg-17 (v4.1)	Calibration of electromechanical and mechanical manometers: Basic, Standard and Comprehensive procedures	Free
EURAMET cg-3 (v2.1)	Calibration of pressure balances (deadweight testers)	Free
USBR 1040-89	A US government procedure for calibrating pressure gauges against a deadweight tester and a master gauge	Free
ASME B40.100 (2022)	US standard for dial pressure gauges, including accuracy grades	Paid
EN 837-1	European standard for Bourdon tube gauges, including accuracy classes	Paid

The reference: a deadweight tester or a reference gauge with a calibration certificate. About four times more accurate than the gauge is the long-standing rule of thumb (Mensor; Fluke); check your ratio with the TUR calculator. Never put a gauge marked for oxygen service on an oil-filled tester (Ashcroft; AIGA SP 09/20).

How often to calibrate a pressure gauge

DKD-R 6-1 leaves the interval to the user and recommends, under normal use, 1 year for Bourdon gauges of class 0.6 or better and electronic gauges of 0.5 % of span or better, 2 years for less accurate ones, and 5 years for deadweight testers (App. F). Twelve months is a common starting point in the US: the Bureau of Reclamation procedure and Ashcroft both use it (USBR 1040-89, §4.2; Ashcroft). Recalibrate after an overload, a repair or rough handling (DKD-R 6-1, App. F), then let your as-found history set the interval: see calibration intervals.

FAQ

What does NIST traceable mean on a digital pressure gauge?

That the gauge's calibration results link to the SI, usually through NIST, by a documented chain of calibrations with stated uncertainties. NIST does not certify traceability claims made by others, so the words alone prove nothing. Ask for the calibration certificate: readings at several pressures across the range, rising and falling, the deviation at each point, the uncertainty, the reference used and its traceability.

Is ±1 % of span the same as ±1 % of reading?

No. Dial gauge grades and classes are a percentage of the span, so the allowed error is the same number of psi everywhere on the dial. On a 0–160 psi gauge, ±1 % of span is ±1.6 psi, which at 20 psi is 8 % of the reading. If you work mostly at the low end of a gauge, a smaller range or a better grade gives you a much smaller error there.

Do gauges marked for oxygen service need special handling during calibration?

Yes. Gauges for oxygen service are cleaned of hydrocarbons and marked USE NO OIL, because oil residue can ignite in oxygen. Never connect one to an oil-filled tester or comparator: calibrate it on separate, clean equipment and keep the media apart.