ISO 10816 Vibration Thresholds Explained for Plant Managers

ISO 10816 is the standard that turns a raw vibration reading into a decision. It sorts a machine's overall vibration velocity (measured in mm/s RMS) into four zones (A, B, C and D) that run from "newly commissioned and healthy" to "damage is likely." The catch: the exact limits depend on the machine's size and how it's mounted, which is where most people get it wrong.

The Four ISO 10816 Zones

Whatever the machine class, the zones always mean the same thing. Only the numeric boundaries between them shift.

• Zone A: vibration of a newly commissioned machine in good condition. Nothing to do.
• Zone B: acceptable for unrestricted long-term operation. Normal running.
• Zone C: unsatisfactory for long-term operation. The machine can run, but plan an intervention. This is your warning line.
• Zone D: vibration severe enough to cause damage. This is your alarm line. Investigate before it fails.

Why the Numbers Change: Machine Class

ISO 10816-3 covers industrial machines above 15 kW, up to about 50 MW, running at 120 to 15,000 r/min. It sorts them into groups by size and by how they are mounted, because a medium pump and a large motor don't vibrate the same way at the same health. Bigger machines and more flexible mountings get wider bands:

• Group 2, medium machines (15 to 300 kW) have the tightest limits in the standard.
• Group 1, large machines (300 kW up to about 50 MW) tolerate more before they cross into the warning zone.
• Mounting changes the limits again. A machine on a flexible support is allowed more vibration than the same machine on a rigid one.

Machines of 15 kW and below are not covered by Part 3. The general part of the series, ISO 10816-1, gives guidance for them.

One more point: in 2022, ISO 20816-3 replaced ISO 10816-3. It covers machines above 15 kW at 120 to 30,000 r/min, and it keeps the same four zones. Many plants and instruments still use the old name, so this post uses both.

Zone boundaries by group and mounting

The table shows the boundary values most often published for the two groups, as overall velocity in mm/s RMS. They are taken from Fabrico's ISO 10816-3 summary. The Group 2 rigid row also matches ACOEM's guide to the severity chart. These are secondary sources. For acceptance tests or contract limits, check the standard itself.

To check a single reading against these limits, use our free vibration threshold lookup.

The practical takeaway: a single site-wide "alarm at X mm/s" rule is almost always wrong. It will nag on large machines that are fine and stay silent on small machines that are already in trouble. The thresholds have to be set per machine class. Very slow parts, such as the tyres and support rollers of a cement kiln, fall outside the zone tables altogether; our guide to predictive maintenance in a cement plant covers what to watch on them instead.

From Threshold to Alert

Knowing the zones is only useful if they drive action. The move most plants make:

• Set the C/D boundary as your alarm and the B/C boundary as your warning, per machine class.
• Watch the trend, not just the absolute value. A reading climbing steadily through Zone B often matters more than one that's sat flat in Zone C for years.
• Pair the overall level with a frequency spectrum so you know why vibration rose. Bearing faults, misalignment and imbalance each show a different signature.

Overall RMS velocity tells you a machine is getting worse. It doesn't tell you what's wrong. That's the difference between a threshold alarm and diagnosis, and it's covered in our companion post on how vibration sensors catch failures.

How Vexron Uses ISO 10816

Vexron applies ISO 10816 zones per machine class automatically, so you don't hand-set a threshold for every asset. Its VMI-1 model goes a step past the standard: instead of only flagging that overall velocity crossed into Zone C, it separates the bearing, alignment and imbalance signatures behind that rise and ranks the alert by severity and trend. Your team then knows both how urgent it is and what to check first. To see how the alerts use these zones on motors, pumps, fans and gearboxes, read our page on online vibration monitoring.