Meters often display peak velocity. For a single-frequency vibration, RMS is the peak divided by 1.41, and this calculator needs the RMS value.
📊 Vibration Severity
Severity Zone Position
Result Breakdown
Full Calculation Table
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How to Use the Vibration Analysis Calculator
Choose the machine class that best matches the equipment being tested, based on power rating and how it's mounted.
Enter the RMS vibration velocity from your vibration meter, typically measured at the bearing housing in a radial direction.
Click Calculate Severity to see which severity zone the reading falls into, marked on a zone bar, along with an interpretation and recommended next steps.
Understanding Vibration Analysis
Rotating equipment vibrates by nature, but the amount of vibration tells a story about mechanical condition long before a failure actually happens. Bearing wear, shaft misalignment, imbalance, and looseness all show up as higher vibration well ahead of the point where a machine actually fails, which makes vibration monitoring one of the most useful predictive maintenance tools available for fans, motors, and compressors.
Severity Zones and the ISO Standards
The severity chart sorts vibration into 4 zones. Zone A represents newly commissioned machines running as expected. Zone B is generally considered acceptable for unrestricted long-term operation. Zone C indicates vibration that's usually considered unsatisfactory for continuous long-term operation, though a machine may operate for a limited period in this zone until a convenient opportunity for repair arises. Zone D indicates vibration severe enough to be considered damaging to the machine. The Class I to IV limits in this calculator come from the legacy ISO 10816-1 chart, which itself replaced ISO 2372. ISO has since withdrawn ISO 10816-1 and revised it as ISO 20816-1:2016, and the criteria for specific machine types now sit in other parts, such as ISO 20816-3:2022 for industrial machines above 15 kW. Treat the zones here as a general screening guide, and use the current ISO 20816 part, the manufacturer's limits, or the project specification when one applies.
Why Machine Class Matters
A small motor and a massive machine on a rigid concrete foundation don't have the same normal vibration range, which is why the zone chart defines separate thresholds for different machine classes. Smaller, more flexibly mounted equipment naturally tolerates and displays somewhat higher vibration than large, rigidly mounted equipment before crossing into a concerning zone, so applying the wrong class to a reading can produce a misleading severity assessment. For HVAC fans specifically, ANSI/AMCA 204 defines balance quality grades and operating vibration levels for fans with rigid rotors in commercial heating, ventilating, and air conditioning. Its limits are written on their own measurement basis, so check whether a limit is peak or RMS before comparing it with a reading, and note that impeller cleanliness, background vibration, and operating speed also affect fan vibration.
Common Causes of Higher Vibration
Unbalanced fan wheels or motor rotors create vibration at a frequency matching the rotating speed, often the most common cause on HVAC fans that accumulate debris or dust unevenly over time. Misalignment between motor and driven equipment produces a distinct vibration signature, frequently at twice running speed. Bearing wear generates higher frequency vibration that often develops gradually, making trending readings over time more valuable than any single reading in isolation. When a blower motor is the suspect, the blower motor diagnosis calculator in troubleshooting helps narrow down the cause.
Trending Matters More Than a Single Reading
A single vibration reading tells you where a machine stands today, but a trend of readings over successive maintenance visits reveals whether a problem is developing. A machine sitting steadily in Zone A or B for years is a different situation than one that has crept from Zone A into Zone C over the last several checks, even if both machines show similar absolute readings on any given visit. Recording readings consistently at the same measurement point and direction each time makes trending meaningful, and the maintenance log calculator in reporting is a handy place to keep the history.
Pairing Vibration Analysis With Electrical Testing
Higher vibration and electrical problems often show up together on the same failing motor. A voltage imbalance can cause uneven heating that eventually affects bearing lubrication and mechanical tolerances, while a worn bearing increases mechanical resistance that shows up as higher amp draw. Pairing vibration analysis with the electrical test calculator gives a more complete diagnostic picture on a suspect motor or compressor.
Frequently Asked Questions
ISO 10816 was a standard framework for evaluating machine vibration severity based on RMS vibration velocity, divided into zones from good through unacceptable, with different limits for different machine classes. ISO has withdrawn ISO 10816-1 and replaced it with ISO 20816-1:2016, and machine-specific criteria now sit in other parts of ISO 20816. This calculator uses the classic Class I to IV zone chart as a general screening guide, so use the current ISO 20816 part or the manufacturer's limits when they apply.
There's no single universal number, since acceptable vibration depends heavily on machine class and mounting type, but a reading that has moved from a good zone into a satisfactory or unsatisfactory zone over successive checks often signals developing bearing wear, misalignment, or imbalance rather than a one-time anomaly.
Critical commercial equipment often gets checked on a regular preventive maintenance schedule, sometimes quarterly or annually depending on the facility's maintenance program. Residential equipment is typically checked reactively when unusual noise or vibration prompts a service call, though a baseline reading at installation gives a useful comparison point if problems develop later.
Readings are typically taken at each bearing housing, in the radial direction perpendicular to the shaft, with vertical and horizontal measurements both useful for a complete picture. Taking readings at the same points and directions on each visit makes trending over time much more meaningful than a single one-off measurement.
For fans specifically, ANSI/AMCA 204 gives balance quality grades and operating vibration levels for fans with rigid rotors in commercial HVAC. Its limits are written on their own measurement basis, so check whether a limit is peak or RMS before comparing it with a reading. The zone chart in this calculator is a general guide for motors and other rotating machines.
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