Why is an oversized isolator a problem?

Because deflection, not rating, produces isolation. A mount rated for 800 lb and carrying 200 lb deflects a quarter of its rated travel. Natural frequency goes as one over the square root of deflection, so a quarter of the deflection doubles the natural frequency, and doubling the natural frequency halves the frequency ratio. A mount that would have isolated 95% at full load might isolate 70%, or amplify, if the machine is slow enough. The load check passes either way, which is what makes it easy to get wrong.

Why does the page publish nothing when the mounts are overloaded?

Because past its rating a mount is outside the linear range this arithmetic assumes, and frequently bottomed out against its own end stop, at which point it is not a spring at all. Extrapolating the linear relationship past the rating produces a confident-looking deflection that has no relationship to what the mount does. Showing nothing and saying why is the honest option.

Should I add more mounts to be safe?

Not for isolation. More mounts share the same weight, so each carries less, deflects less, and has a higher natural frequency: the isolation gets worse. Extra mounts help with stability, load distribution across a long base, or a genuinely overloaded condition, but if you add them you should soften them proportionally or you have downgraded the installation.

Springs or elastomeric mounts?

Deflection decides it. Elastomeric mounts and pads typically offer a tenth to half an inch, giving natural frequencies around 5 to 10 Hz, which is fine for machinery above roughly 1200 rpm. Steel springs offer one to three inches and natural frequencies of 2 to 3 Hz, which is what slow machinery needs. Springs also stay linear to rating and do not creep, at the cost of poor high-frequency performance unless fitted with an elastomeric pad in series.

The weight is not evenly distributed. What should I enter?

Run the worst-loaded mount separately: enter its share of the weight as the operating weight with a count of one. Uneven loading means the mounts deflect by different amounts, which tilts the machine and creates rocking modes this single-degree-of-freedom model does not cover. Suppliers handle it by specifying different mounts at different positions so every corner reaches the same deflection.

Does this tell me whether the machine will be quiet?

No. It tells you what deflection and natural frequency the mount selection produces. Whether that isolates depends on the machine's running speed, which is the Resonance Frequency Check, and how much gets through, which is the Isolation Efficiency page. All three use the same deflection, which is why measuring it properly matters more than any other input in this category.

Acoustic, Noise, Vibration & NVH Products calculator

Vibration Isolator Load and Deflection Calculator

Check a set of vibration isolators against the machine they will carry. Enter the equipment's operating weight, how many mounts share it, the mount's rated load and the deflection it shows at that rating. The calculator returns the load on each mount, how much of the rating is being used, the static deflection that results, and the natural frequency that deflection produces. Holding the weight is the easy part and nearly any mount on the shortlist manages it; whether the mount isolates depends entirely on how far it actually sinks, which is what this page makes visible.

What this calculator does

Check a set of isolators against the machine they carry: load per mount, how much of the rating is used, the deflection that results, and the natural frequency that deflection produces.
Use it for verifying a supplier's mount selection before the order goes out, diagnosing why a machine on correctly rated mounts still transmits vibration, deciding between four soft mounts and six stiffer ones, checking the worst-loaded corner of a machine with an offset drive, converting a mount catalogue into the natural frequency the isolation calculation needs.
Check a set of isolators against the machine they carry: load per mount, how much of the rating is used, the deflection that results, and the natural frequency that deflection produces.

Formula used

Load per isolator = equipment operating weight ÷ number of isolators
Rating utilization = load per isolator ÷ rated load × 100
Static deflection = rated deflection × (load per isolator ÷ rated load)
Natural frequency = 3.13 ÷ √(static deflection in inches)
Total isolator rating = rated load × number of isolators

Inputs explained

Equipment operating weight: Total weight the mounts carry when the machine is running, including any fluid, product or inertia base. Not the shipping weight.
Number of isolators: How many mounts share the load. More mounts is not better: the same weight spread further deflects each one less.
Rated load per isolator: The mount's catalogue load rating, per mount.
Rated deflection at rated load: How far the mount deflects when loaded to its full rating, from the catalogue. This is the number that decides isolation, and it is the one most often left off a quote.

How to use the result

Best suited to verifying a supplier's mount selection before the order goes out, diagnosing why a machine on correctly rated mounts still transmits vibration, deciding between four soft mounts and six stiffer ones, checking the worst-loaded corner of a machine with an offset drive, converting a mount catalogue into the natural frequency the isolation calculation needs.
Does not check the mount's own strength, temperature rating, chemical compatibility or fatigue life. Says nothing about lateral or rocking stability, which soft mounts under a tall machine can lose long before the vertical load becomes a problem. Publishes nothing past the rating, because deflection there depends on how the specific mount fails rather than on any formula. Assumes even weight distribution. A machine with an offset motor loads one corner far harder, and that corner governs. Not a seismic or wind restraint calculation.

Common questions

Why is an oversized isolator a problem? Because deflection, not rating, produces isolation. A mount rated for 800 lb and carrying 200 lb deflects a quarter of its rated travel. Natural frequency goes as one over the square root of deflection, so a quarter of the deflection doubles the natural frequency, and doubling the natural frequency halves the frequency ratio. A mount that would have isolated 95% at full load might isolate 70%, or amplify, if the machine is slow enough. The load check passes either way, which is what makes it easy to get wrong.
Why does the page publish nothing when the mounts are overloaded? Because past its rating a mount is outside the linear range this arithmetic assumes, and frequently bottomed out against its own end stop, at which point it is not a spring at all. Extrapolating the linear relationship past the rating produces a confident-looking deflection that has no relationship to what the mount does. Showing nothing and saying why is the honest option.
Should I add more mounts to be safe? Not for isolation. More mounts share the same weight, so each carries less, deflects less, and has a higher natural frequency: the isolation gets worse. Extra mounts help with stability, load distribution across a long base, or a genuinely overloaded condition, but if you add them you should soften them proportionally or you have downgraded the installation.
Springs or elastomeric mounts? Deflection decides it. Elastomeric mounts and pads typically offer a tenth to half an inch, giving natural frequencies around 5 to 10 Hz, which is fine for machinery above roughly 1200 rpm. Steel springs offer one to three inches and natural frequencies of 2 to 3 Hz, which is what slow machinery needs. Springs also stay linear to rating and do not creep, at the cost of poor high-frequency performance unless fitted with an elastomeric pad in series.
The weight is not evenly distributed. What should I enter? Run the worst-loaded mount separately: enter its share of the weight as the operating weight with a count of one. Uneven loading means the mounts deflect by different amounts, which tilts the machine and creates rocking modes this single-degree-of-freedom model does not cover. Suppliers handle it by specifying different mounts at different positions so every corner reaches the same deflection.

Last reviewed 2026-08-25.