Pressure Gauge Accuracy Classes Explained: The EN 837 Standard

Last updated: September 2026

You’ve seen the numbers printed on every pressure gauge dial — 0.1, 0.25, 0.6, 1.0, 1.6, 2.5, 4.0 — but what do they actually mean, and does paying for a Class 0.25 gauge make sense when a Class 1.6 would do the job?

Accuracy class is one of the most misunderstood specifications in pressure measurement. Engineers over-specify because they’re unsure; procurement teams under-specify to hit budget targets. Neither serves the process.

This guide explains what accuracy classes mean, how each one maps to real applications, and how to choose the right class — without overpaying or compromising safety.

Throughout, we reference the EN 837 standard, the European norm that defines the seven standard accuracy classes for Bourdon tube pressure gauges. We manufacture gauges across the classes from 0.25 to 2.5 (the range most industrial applications actually use), but a complete understanding of the full EN 837 scale — from 0.1 up to 4.0 — will help you specify correctly, even when a class sits outside our own catalogue.

What Accuracy Class Actually Means

Accuracy class defines the maximum permissible error of a pressure gauge, expressed as a percentage of the full-scale reading. A Class 1.6 gauge on a 0–10 bar range, for example, can deviate by up to ±0.16 bar (1.6% of 10 bar) at any point on the scale.

This is a full-scale specification, not a reading specification. At half scale — 5 bar on that same gauge — the error is still up to ±0.16 bar, which is now ±3.2% of the reading. This is why selecting a range close to your operating pressure matters just as much as selecting the accuracy class itself.

Standard accuracy classes are defined by EN 837 for Bourdon tube pressure gauges, running from 0.1 through 4.0. The table below shows the full seven-class scale and how each relates to error and typical use. (Upscale Gauge manufactures the 0.25 to 2.5 range — highlighted below.)

Accuracy Class	Max Permissible Error (% of full scale)	Typical Application
0.1	±0.1%	Precision laboratory, metrology reference
0.25	±0.25%	Laboratory, calibration reference ✔
0.6	±0.6%	Standard industrial process ✔
1.0	±1.0%	General process measurement ✔
1.6	±1.6%	General-purpose industrial ✔
2.5	±2.5%	Utility, non-critical indication ✔
4.0	±4.0%	Non-critical, coarse indication only

Breaking Down Each Class

Class 0.1 — Precision Metrology Reference

Class 0.1 sits at the top of the EN 837 scale and is reserved for precision laboratory and metrology work — master gauges used to verify other instruments, and standards in national metrology labs. These are delicate reference instruments, not process gauges, and their cost and handling requirements put them far outside routine industrial use.

Typical use: master reference standards, precision calibration labs.
The common mistake: confusing Class 0.1 with “slightly better than 0.25.” The two are different categories of instrument entirely — a Class 0.1 gauge needs controlled temperature, careful handling, and frequent calibration to hold its rating.

Unless you operate a calibration laboratory, you almost certainly don’t need Class 0.1.

Class 0.25 — Laboratory and Reference

Class 0.25 gauges are reference and test instruments, not process gauges. You’ll find them in calibration labs, metrology departments, and as standards for verifying other instruments.

Typical use: calibrating production gauges, laboratory research, applications where legal metrology or custody transfer applies.
The common mistake: specifying Class 0.25 for routine process measurement. If your process tolerance is ±5%, a Class 0.25 gauge won’t improve the process — it’ll only inflate the procurement budget.

Unless you’re calibrating other instruments or meeting legal metrology requirements, you likely don’t need Class 0.25.

Class 0.6 — Standard Industrial Process

Class 0.6 is the step up for process measurements that need dependable precision without entering laboratory territory. It’s often chosen where readings influence quality decisions but not at the extreme end of precision.

Typical use: chemical and pharmaceutical batching, compressor discharge monitoring, hydraulic test stands where a tighter error band is required.
Why choose 0.6 over 1.0: on a 0–40 bar gauge, Class 0.6 gives ±0.24 bar against Class 1.0’s ±0.4 bar. When your safety or quality margin is measured in tenths of a bar, that gap matters.

Class 1.0 — General Process Measurement

Class 1.0 sits between the precision classes and the general-purpose workhorse. It offers better accuracy than 1.6 at a moderate premium, making it a good middle ground for process control.

Typical use: hydraulic systems, heat exchangers, reactors where operators want a tighter reading without paying for reference-grade precision.

Class 1.6 — The Workhorse of Industrial Measurement

Class 1.6 is the most widely specified accuracy class for good reason: it balances precision with cost, and for the vast majority of industrial processes it is more than adequate.

Typical use: water treatment, HVAC, compressed air, general chemical processing, food and beverage, oil and gas utilities.
Why it’s the sweet spot: on a 0–10 bar gauge you get ±0.16 bar accuracy — sufficient for most pump discharge, filter differential, and tank-level decisions.

The key insight: if your process tolerates a 1.6% deviation at full scale, there is no engineering reason to pay for higher accuracy.

Class 2.5 — Utility and Non-Critical Indication

Class 2.5 gauges are for indication, not precision — “is the system pressurized or not?” instruments.

Typical use: fire protection systems, low-pressure HVAC, utility water, visual status checks on non-critical lines.
What to watch for: don’t use Class 2.5 for safety-related measurements. If a reading triggers a safety decision, even indirectly, you need at least Class 1.6.

Class 4.0 — Coarse, Non-Critical Indication Only

Class 4.0 is the coarsest class in the EN 837 scale, at the bottom of the range. It is only suitable for the most basic “is there pressure or not” indication where accuracy is essentially irrelevant.

Typical use: very low-cost, non-critical visual indication on utility lines where no decision depends on the reading.
What to watch for: Class 4.0 should never be used where a reading influences any safety, quality, or process decision. For most modern industrial applications, Class 2.5 is the practical floor.

The Full-Scale Trap

Here’s a scenario we see often: a facility specifies a Class 1.6 gauge with a 0–100 bar range to measure a process running at 10 bar. The maximum error is ±1.6 bar — which is ±16% of the actual operating point. That’s effectively Class 16 at the operating pressure.

The rule of thumb: select a range so your normal operating pressure falls between 25% and 75% of full scale. For that 10 bar process, a 0–16 bar gauge at Class 1.6 gives ±0.256 bar error — about ±2.56% of the reading. Same accuracy class, dramatically better real-world precision.

How to Choose the Right Accuracy Class

Use this decision sequence:

Is the reading safety-critical? → minimum Class 1.0, consider Class 0.6 or 0.25 for tight margins.
Does the reading directly affect product quality or compliance? → Class 0.6 or 1.0.
Is it general process monitoring? → Class 1.6.
Is it utility or non-critical indication? → Class 2.5.

Then verify your range: normal operating pressure should sit between 25% and 75% of full scale.

Calibration and Verification

Choosing the right class is only half the battle — maintaining that accuracy in service requires a calibration plan.

Suggested calibration intervals:

Class 0.25 — annually (reference-grade)
Class 0.6 and 1.0 — every 12–18 months
Class 1.6 — every 18–24 months
Class 2.5 — every 24–36 months

Signs of drift: the pointer doesn’t return to zero when depressurized, the needle sticks, or the gauge disagrees with a redundant instrument. Any of these means it’s time to recalibrate or replace.

Conclusion

Accuracy class is a critical specification — but it’s not the only one. The best-engineered pressure measurement system is one where accuracy class, gauge range, fill type, connection standard, and material compatibility all work together to match the application.

Don’t over-specify accuracy to compensate for poor range selection, and don’t under-specify to save on initial cost when long-term calibration drift will cost more. Get the fundamentals right, and Class 1.6 will serve you well in the vast majority of industrial applications.

At Upscale Gauge we manufacture gauges across accuracy classes from 0.25 to 2.5 (per EN 837), with ranges from a few kPa to 160 MPa plus vacuum and materials from copper alloy to 316L stainless steel. If you need help selecting the right class for your process, our technical team is here to help.

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Pressure Gauge Accuracy Classes Explained: What EN 837 Really Means for Your Process