Read the guide: How accurate is a phone vibration meter?
How to use the vibration severity chart
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Step 1: Pick the machine class. Small motors and machines up to 15 kW (about 20 hp) are class I. The table below explains the rest.
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Step 2: Enter the vibration as RMS velocity in mm/s. Have peak in/s instead? Multiply it by about 18, or use the vibration unit converter.
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Step 3: Read the zone: A is good, B is acceptable, C means plan a fix, and D means risk of damage.
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Step 4: Need a reading? Measure with the machine vibration test and use the RMS velocity from the result details.
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Step 5: Measure the same spot the same way every few weeks. A rising trend tells you more than any single reading.
A vibration severity chart turns one number, RMS velocity in mm/s, into a verdict: is this machine running well, fine for now, or heading for damage? The zones on this page come from ISO 10816-1, the long-standing general standard for machine vibration. It sorts machines into four size classes, because a big machine on a soft foundation naturally moves more than a small motor bolted to the floor.
ISO 10816 vibration severity chart
Zone boundaries in mm/s RMS:
| Class | Typical machines | A/B | B/C | C/D |
|---|---|---|---|---|
| I | Small machines, such as electric motors up to 15 kW | 0.71 | 1.8 | 4.5 |
| II | Medium machines, 15 to 75 kW, or up to 300 kW on special foundations | 1.12 | 2.8 | 7.1 |
| III | Large machines on rigid, heavy foundations | 1.8 | 4.5 | 11.2 |
| IV | Large machines on soft foundations, such as big turbine sets | 2.8 | 7.1 | 18 |
Read it like this. For a class II machine, below 1.12 mm/s is zone A, 1.12 to 2.8 is zone B, 2.8 to 7.1 is zone C, and above 7.1 is zone D.
The values are broadband RMS velocity, measured on the bearing housings, usually over about 10 to 1,000 Hz. US reports often give peak velocity in in/s instead. For class I, the boundaries are about 0.04, 0.10 and 0.25 in/s peak.
What each zone means
- Zone A, good. Where a newly commissioned machine should be. No action needed.
- Zone B, acceptable. Fine for unrestricted long-term running. Measure now and then to spot changes.
- Zone C, unsatisfactory. Not suitable for long-term continuous running. It can usually run for a limited time, but plan a repair at the next good chance.
- Zone D, damaging. Vibration this high is normally severe enough to damage the machine. Stop it and find the cause before you run it again, if you can do so safely.
These zones are a general guide. A machine maker’s own limits, or a part of the standard written for that type of machine, come first.
How this site’s machine labels match the zones
The sensor tools for appliances, cars and machines use the class I numbers. The ceiling fan pages use their own wobble scale (2.5, 8 and 16 mm/s RMS), because a fan’s slow sway would read as Rough here; see why fans get their own scale. The machine labels match the zones like this:
| Label on this site | Zone | RMS velocity |
|---|---|---|
| Smooth | A | under 0.71 mm/s |
| Normal | B | 0.71–1.8 mm/s |
| Rough, check it | C | 1.8–4.5 mm/s |
| Too much vibration | D | over 4.5 mm/s |
What to do about a high reading
If a machine is in zone C or D, these are the usual suspects:
- Imbalance. A heavy spot on a rotor, fan or pulley. It shakes once per turn, at 1× running speed. Clean dirt off fan blades and have rotors balanced.
- Looseness. Loose mounting bolts, a cracked base or worn feet. It often shows up at 2× running speed and above. Tighten the bolts and check the base.
- Misalignment. Shafts that don’t line up across a coupling or belt drive. It often shows at 1× and 2× running speed.
- Resonance. The running speed matches a natural frequency of the frame or base, so a small force makes a big shake. Changing the speed or stiffening the mount helps.
- Bearing wear. It usually starts at high frequencies a phone can’t measure. Listen for grinding or rumbling and feel for heat.
Use the RPM to Hz converter to find the 1× and 2× frequencies for your machine. For anything expensive, critical or in zone D, call a vibration analyst or the maker’s service team. They measure each bearing with calibrated sensors and can tell these causes apart.
Where the numbers come from
The class boundaries are the classic example zones from ISO 10816-1, which has since been replaced by ISO 20816-1. They are widely used as a rough guide, not a pass or fail test for your machine. Standards for specific machine types, such as large industrial machines or pumps, set their own limits.
Frequently asked questions
What is an acceptable vibration level for a small motor?
For a class I machine, such as a motor up to 15 kW, under 1.8 mm/s RMS is acceptable for long-term running. Under 0.71 mm/s is typical of a new machine in good condition. Always check the maker's own limits first.
Is ISO 10816 still valid?
ISO 10816-1 has been replaced by ISO 20816-1, and several machine-specific parts have moved to the 20816 series too. The classic class I to IV zones are still widely used as a rough guide, which is how this chart uses them.
Why does the chart use RMS velocity?
Velocity links well to wear and fatigue across the speeds of most everyday machines, so one limit works for many speeds. RMS averages the size of the vibration over time instead of catching a single spike.
Can I use this chart for a washing machine or a car?
Only loosely. The zones were written for industrial machines measured on the bearing housings with a proper sensor. The appliance tools on this site use the class I numbers as a rough guide. The car tools use them too, but ordinary road shake can read high on this scale, so compare a run at the shaky speed with one at a calm speed. A car should be judged against its maker's service information, not ISO 10816.
Can I judge a machine with my phone's reading?
As a first check, yes. A phone measures up to about 30 Hz, while the standard covers roughly 10 to 1,000 Hz, so a phone can miss fast vibration and read low. Treat a phone reading as a good guide, not a certified measurement.
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