How Bumpy?

How it works

What the number means

Your phone's motion sensor feels every shake. The page weights them with the comfort weightings published in ISO 2631-1:1997, the international standard on whole-body vibration: people feel up-and-down shaking most at about 4 to 12 times a second, and side-to-side or front-to-back swaying most at about once or twice a second. The result is one number in m/s² (metres per second squared). The standard gives a rough guide to how passengers react to it; these are its descriptions:

The ranges overlap on purpose, because people differ. Where two overlap, this page switches label halfway through the overlap. Comfort is about much more than vibration (noise, temperature, the seat, how you sit), and none of that is measured here.

Where to put the phone

Lay it flat on the seat, ideally in the same spot every time. Any way up is fine: the page works out which way is down. On your lap or in your hand, your body softens the shaking; standing, it measures the floor; either way the numbers aren't comparable with a phone on the seat. Picking the phone up spoils the reading, so those seconds are left out automatically, as is any time without readings, plus a couple of seconds after each break while the calculation settles.

Measuring stops by itself after two hours, or if the readings stop for five minutes.

Seasickness

ISO 2631-1 also gives a motion-sickness dose for slow up-and-down swaying, the kind boats make, and a rough rule for how many people that much motion would make vomit. It builds up over time, so it means most on rides of 20 minutes or more. Car sickness comes mostly from braking and cornering, which this dose doesn't count.

Limits

This is a bit of fun, not a measuring instrument. Your phone hasn't been calibrated or checked against a reference sensor, and phones differ, so compare rides from the same phone placed the same way rather than across phones. It measures one spot and only straight-line shaking, not rotation. "Up and down" means along gravity, so in a reclined seat or a vehicle that banks or pitches the split between up-and-down and sideways is approximate. Phones typically report motion about 60 times a second (each ride's technical details show the real rate): shaking faster than about half that rate isn't measured, and can even show up as slower shaking. The standard covers shaking up to 80 times a second. Jolt sizes are approximate, and a sensor can top out on a big knock. The standard itself is being revised. Never use these numbers for safety, health or work-exposure decisions.

Privacy

Everything is worked out on your phone. Nothing is uploaded, no location is used, and there are no cookies or analytics. Saved rides stay in this browser, and you can delete them all from the list of your rides.

Questions