Acceptable Vibration Levels for Motors, Pumps, Fans, Compressors & Gearboxes (mm/s Guide)

If you have taken a vibration reading and you are staring at a number in millimetres per second (mm/s) wondering whether it is fine or a warning sign, here is the short answer: for most general-purpose industrial machines, a reading below about 2.8 mm/s RMS is healthy, 2.8–4.5 mm/s means keep an eye on it, and above 4.5 mm/s usually calls for action. But the exact acceptable vibration level for an electric motor — or a pump, fan, compressor, gearbox or blower — depends on the machine’s size, how it is mounted, and which standard applies.

This guide breaks down the real numbers from ISO 10816-3 (the most widely used industrial vibration standard), gives you a practical mm/s cheat-sheet by equipment type, and shows you how to take a reliable reading in seconds. You do not need a $3,000 data collector to get started — a modern smartphone’s accelerometer is sensitive enough for screening and trending, and the free Vibration Detector Sensor app turns your iPhone into a live RMS vibration meter.

Measure your machine’s vibration in 30 seconds

Place your phone on the bearing housing, read the live RMS value in mm/s, and compare it to the ISO zones below. No external sensor required.

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What “acceptable vibration” actually means

When technicians talk about an acceptable vibration level, they are almost always referring to overall RMS velocity, measured in mm/s (or inches per second in the US). RMS — root mean square — represents the energy content of the vibration over time, which correlates better with fatigue damage than a single peak spike. That is why standards bodies settled on RMS velocity as the go-to severity metric for rotating machinery running between roughly 120 and 15,000 RPM.

Velocity is preferred over acceleration or displacement because it stays relatively flat across the frequency range where most machine faults live (imbalance, misalignment, looseness). If you want to understand the difference between these measurements, the vibration meter landing page explains how acceleration, velocity and displacement relate — but for go/no-go decisions, mm/s RMS velocity is the number that matters.

Quick rule of thumb: For a typical 15–300 kW machine on a rigid foundation, treat 2.8 mm/s as your “investigate” threshold and 4.5 mm/s as your “plan a repair” threshold. Smaller machines are stricter; larger or flexibly mounted machines tolerate more.

The ISO 10816-3 vibration severity zones (A, B, C, D)

ISO 10816-3 (now being superseded by ISO 20816-3, which uses the same numbers) divides machine vibration into four zones. Measurements are taken in velocity (mm/s RMS) on the bearing housings or machine feet, in the horizontal, vertical and axial directions.

Zone	Condition	What it means
A	Newly commissioned	Like-new or freshly overhauled equipment in excellent condition.
B	Acceptable	Suitable for unrestricted long-term operation. Most healthy machines live here.
C	Unsatisfactory	Not for long-term running. Investigate the cause and plan corrective maintenance.
D	Dangerous	Risk of imminent damage. Shut down and correct as soon as practical.

The actual mm/s boundaries between these zones change with machine size (Group 1 = large machines above 300 kW; Group 2 = medium machines 15–300 kW) and support type (rigid vs. flexible). Here are the standard zone-boundary values:

Machine class & support	A/B (mm/s)	B/C (mm/s)	C/D (mm/s)
Group 2 (15–300 kW) — Rigid	1.4	2.8	4.5
Group 2 (15–300 kW) — Flexible	2.3	4.5	7.1
Group 1 (>300 kW) — Rigid	2.3	4.5	7.1
Group 1 (>300 kW) — Flexible	3.5	7.1	11.0

So a 75 kW motor on a rigid base reading 3.5 mm/s sits in Zone C — running, but you should schedule attention. The same reading on a flexibly mounted 500 kW machine is comfortably in Zone B. Context is everything, which is why a live mm/s vibration reading from the app is only step one — you then map it to the right row above.

Acceptable vibration levels by machine type

While ISO 10816-3 covers most general rotating equipment, some machines have their own dedicated standards. Here is a practical screening table for typical small-to-medium units on a rigid mount. Use it for trending and triage, then confirm against the specific standard for compliance work.

Equipment	Good (mm/s)	Monitor (mm/s)	Act (mm/s)	Standard
Electric motor	< 2.8	2.8–4.5	> 4.5	ISO 10816-3
Centrifugal pump	< 2.8	2.8–4.5	> 4.5	ISO 10816-7
Fan / blower (industrial)	< 4.5	4.5–7.1	> 7.1	ISO 14694
Rotary compressor	< 2.8	2.8–4.5	> 4.5	ISO 10816-3
Reciprocating compressor	varies	—	varies	ISO 10816-6
Gearbox	< 2.8	2.8–4.5	> 4.5	ISO 8579-2

Electric motors

The acceptable vibration level for an electric motor follows ISO 10816-3 directly. For a standard 15–300 kW motor on a rigid base, aim for under 2.8 mm/s; small fractional-kW motors should be stricter (closer to 1.8 mm/s). A rising 1×RPM component almost always points to imbalance, while a strong 2×RPM peak suggests misalignment — both easy to spot once you check the frequency spectrum in the vibration sensor app.

Pumps

Centrifugal pumps are formally covered by ISO 10816-7, but the practical bands mirror motors. Watch for vibration that climbs near the blade-pass frequency (number of impeller vanes × RPM), which can indicate cavitation or recirculation. A pump that creeps from 2.0 to 3.5 mm/s over a few weeks is trending toward trouble — trend logging on the accelerometer tool makes that climb obvious.

Fans and blowers

Fans get their own standard, ISO 14694, and generally tolerate slightly higher vibration than tightly toleranced machines — many industrial fans are acceptable up to 4.5 mm/s, though HVAC and clean-room fans are held tighter. Large overhung fan rotors are sensitive to dust build-up on the blades, which shows up as a slowly rising 1×RPM imbalance. Precision-grade HVAC blowers should be treated more like motors.

Compressors

Rotary and centrifugal compressors are typically evaluated with ISO 10816-3, so the motor-style bands apply. Reciprocating compressors are a different animal — they generate inherently higher vibration and are governed by ISO 10816-6, often with acceleration-based limits. Do not judge a reciprocating unit against motor numbers; you will get false alarms every time.

Gearboxes

Gearboxes are tricky because gear-mesh frequencies are high, so a healthy gearbox can show modest velocity but significant acceleration (g). Use ISO 8579-2 or 10816-3 for the velocity overall, but always check acceleration too — gear and bearing defects often appear in the high-frequency band long before the mm/s velocity reading moves.

⚠ Important: These thresholds assume measurements taken at the bearing housing under steady-state, full-load conditions. Readings taken on a guard, sheet-metal cover or at idle are not comparable. Always measure at the same point, in the same direction, under the same load — consistency is what makes trending meaningful.

How to measure vibration on your equipment

You have two options: a dedicated handheld vibration meter (accurate but expensive), or your smartphone’s built-in three-axis accelerometer (free, surprisingly capable for screening). For trending overall mm/s, spotting imbalance, and catching a machine that is degrading week over week, a phone is more than enough — which is exactly the use case professional forums recommend it for.

To take a clean reading: stop the machine, press your phone firmly and flat against the bearing housing (a thin foam pad improves coupling), restart, let the reading stabilise for a few seconds, and record the RMS velocity in mm/s. Repeat in the horizontal, vertical and axial directions. The Vibration Detector Sensor app shows live RMS, peak, and a frequency spectrum, and lets you log sessions and export them to CSV for your maintenance records — see the full feature list on the app’s home page.

What to do when readings are too high

A high overall mm/s number tells you something is wrong; the frequency spectrum tells you what. As a starting point: vibration at 1×RPM means imbalance; 2×RPM means misalignment or a bent shaft; high-frequency energy points to bearing or gear defects; and a non-synchronous peak can signal looseness or resonance. Open the spectrum view in the app, note the dominant frequency, and convert it to a multiple of running speed to narrow down the fault.

✓ Pro tip: Record a baseline reading on every healthy machine today. A single number means little in isolation, but a 40% rise from a known-good baseline is an unambiguous early warning — often weeks before the machine reaches Zone C.

Start trending your machines for free

Live RMS & peak in mm/s, frequency spectrum with dominant-peak detection, session logging and CSV export — all from your iPhone. Build a baseline today and catch failures before they catch you.

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Note: A smartphone accelerometer is excellent for screening, trending and education, but it is not a substitute for a certified vibration analyser when compliance-grade, calibrated measurements are required. Use professional instrumentation for acceptance testing and warranty work.

Frequently Asked Questions

What is an acceptable vibration level for an electric motor in mm/s?

For a typical 15–300 kW electric motor on a rigid foundation, an acceptable vibration level is under 2.8 mm/s RMS velocity (ISO 10816-3 Zone B). Readings of 2.8–4.5 mm/s are unsatisfactory and should be investigated, and anything above 4.5 mm/s is considered dangerous for long-term running. Smaller motors should be held to stricter limits.

What vibration level is too high for a motor?

For most medium motors, vibration above 4.5 mm/s RMS (Zone D) is too high and indicates a real risk of damage — you should plan a shutdown and repair. Between 2.8 and 4.5 mm/s the motor can keep running short-term while you diagnose and schedule corrective work.

What is a normal vibration reading for a pump?

A healthy centrifugal pump typically reads below 2.8 mm/s RMS at the bearing housings. Vibration concentrated at the blade-pass frequency can indicate cavitation or flow recirculation, while a rising 1×RPM peak usually points to imbalance or coupling wear.

How many mm/s of vibration is dangerous?

It depends on machine size and mounting, but as a general guide anything in ISO 10816-3 Zone D — above 4.5 mm/s for medium rigid-mounted machines, or above 7.1–11 mm/s for large or flexibly mounted machines — is dangerous and warrants prompt action.

What is the difference between ISO 10816-3 zones A, B, C and D?

Zone A is newly commissioned (like-new) condition; Zone B is acceptable for unrestricted long-term operation; Zone C is unsatisfactory, meaning the machine can run only short-term while you plan repairs; and Zone D is dangerous, requiring corrective action to avoid failure. The mm/s boundaries between zones scale with machine power and support stiffness.

Can I measure motor vibration with my phone?

Yes. Modern smartphones contain a sensitive three-axis accelerometer that can measure overall RMS velocity and display a frequency spectrum, making them well suited to screening and trend monitoring. A phone-based vibration meter such as the Vibration Detector Sensor app is widely used for daily checks and baselining, though it does not replace a calibrated analyser for compliance-grade measurement.

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