Read the guide: Vibration frequency explained
How to convert Hz to RPM
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Step 1: Type the frequency in hertz (Hz). Decimals are fine, like 12.5.
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Step 2: Read the result in RPM. It updates as you type.
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Step 3: To go the other way, type the RPM instead and read the Hz.
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Step 4: Got the frequency from a vibration reading? Compare the RPM with the known speed of each spinning part to find the one that matches.
Hz to RPM takes one step: multiply by 60. Hertz counts cycles per second, and RPM counts revolutions per minute. The usual reason to convert is a vibration reading. Your phone tells you how fast something shakes in Hz, but the parts in a car, washer or motor are rated in RPM. Once both are in RPM, you can see which part matches.
Hz to RPM formula
RPM = Hz × 60
One hertz is one cycle per second. A spinning part with a heavy spot shakes once per turn, so each turn makes one cycle. That means 1 Hz is one turn per second, or 60 RPM.
To go back, divide by 60: Hz = RPM ÷ 60. The RPM to Hz converter covers that direction in detail.
Worked examples
- Washing machine. Your phone reads 12.5 Hz on the spin cycle. 12.5 × 60 = 750 RPM. That’s within the usual 600 to 900 RPM spin range of many top-loaders, so the drum is the likely source.
- Car at highway speed. A passenger measures 11.8 Hz at 60 mph. 11.8 × 60 = 708 RPM. A 225/65R17 tire turns about 707 times a minute at 60 mph, which points to a wheel or tire. The tire vibration frequency calculator works this out for your tire size.
- Ceiling fan. The wobble shows 1.2 Hz. 1.2 × 60 = 72 RPM, a normal low speed for many ceiling fans.
Hz to RPM table
| Hz | RPM | Something that shakes at this rate |
|---|---|---|
| 0.5 | 30 | A pendulum on a 1 m string |
| 1 | 60 | A ceiling fan on low |
| 2 | 120 | |
| 5 | 300 | |
| 10 | 600 | A top-loader spin, low end |
| 12.5 | 750 | An engine crankshaft at a 750 RPM idle |
| 15 | 900 | A top-loader spin, high end |
| 20 | 1,200 | A front-loader spin |
| 25 | 1,500 | A 4-cylinder engine firing at a 750 RPM idle |
| 30 | 1,800 | About the fastest most phones can measure |
| 60 | 3,600 | A fixed-speed fridge compressor (too fast for a phone) |
Notice the 25 Hz row. The engine turns at 750 RPM, but a 4-cylinder engine fires twice per turn, so it shakes at 1,500 cycles a minute. A frequency tells you how often something happens, not always how fast one part spins.
Matching a vibration to a part
A frequency alone doesn’t name the cause. These patterns help:
- 1× the part’s speed. The vibration in RPM equals the part’s RPM. This is most often imbalance, a heavy spot on a wheel, fan blade or drum.
- 2× the part’s speed. Often misalignment, loose mounting, or a tire that isn’t perfectly round.
- Blades or cylinders. A fan can shake at its speed times the number of blades. A 4-stroke engine fires at RPM ÷ 60 × cylinders ÷ 2.
If nothing matches, the real vibration may be faster than your phone can measure. Phones take about 60 readings a second, so they can read up to about 30 Hz (1,800 RPM). Faster shaking can show up as a false, lower frequency.
Where the numbers come from
The factor of 60 is simply the number of seconds in a minute. The example speeds in the table are typical ranges, not specs for your machine. Check the manual or the maker’s support page for your model’s exact speed. The wheel example uses a tire diameter of about 724 mm for a 225/65R17 tire.
Frequently asked questions
How many RPM is 1 Hz?
1 Hz is exactly 60 RPM. One hertz means one full cycle per second, and there are 60 seconds in a minute.
Is Hz the same as revolutions per second?
For something that spins, yes. One revolution per second is 1 Hz. Hertz is more general, though: it counts any repeating cycle, like a vibration or a sound wave, not just a turn.
Why doesn't my vibration frequency match any part's RPM?
Vibration often shows up at 2× or 3× a part's speed, or at a rate set by the number of blades or cylinders. It can also be a false, lower frequency if the real vibration is faster than about 30 Hz, the limit of most phones. The vibration frequency analyzer shows the top 3 peaks to help you sort this out.
How do I convert Hz to rad/s?
Multiply Hz by 2π, about 6.283. So 10 Hz is about 62.8 rad/s. To get RPM from rad/s, multiply by about 9.549.
Can I convert an electric motor's 60 Hz to RPM?
Not directly. The 60 Hz on the nameplate is the power supply, not the shaft speed. How fast the shaft turns depends on the motor's number of poles. A common 4-pole motor on 60 Hz power turns at a bit under 1,800 RPM.
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