# How is turbulence measured? g, EDR, pilot reports and your phone

**Short answer:** Turbulence is measured in three ways. Accelerometers measure how many g a bump adds or takes away. Airliners' computers turn their sensor data into the eddy dissipation rate (EDR), the official ICAO and WMO measure of the air itself. And pilots report light, moderate, severe or extreme by feel. Your phone's accelerometer can measure the g you feel at your seat.

## Key facts
- The eddy dissipation rate (EDR) is the official atmospheric turbulence intensity metric of ICAO and the World Meteorological Organization. [1][2]
- For a medium-sized transport aircraft, ICAO counts an EDR peak above 0.10 as light, from 0.20 as moderate and from 0.45 as severe. [2]
- WMO guidance ties moderate turbulence to accelerometer changes of 0.5 to 1.0 g at the aircraft's center of gravity, and severe to more than 1.0 g. [3]
- US airlines began calculating turbulence intensity objectively from aircraft sensors in 1997. [1]
- IATA's Turbulence Aware platform lists more than 3,000 reporting aircraft from more than 30 airlines, and more than 60 million EDR reports received in 2025. [4]
- In one Boeing 737-900ER turbulence accident, peak load factors in the rear cabin were about 0.2 g larger than at the center of gravity. [1]

## Three ways to measure turbulence
Turbulence is uneven air: eddies and up-and-down currents that bump an airplane. There's no single "turbulence meter" in the cockpit. Instead, three kinds of measurement work side by side.

| Method | What it measures | Strength | Limit |
|---|---|---|---|
| **g (accelerometers)** | How hard the airplane, or a spot in its cabin, is pushed up or down | Objective, instant | Depends on the airplane and on where you measure [1] |
| **EDR** | How turbulent the air itself is | Objective, the same for every aircraft size [1] | Needs equipment and software tuned for each type [1] |
| **Pilot report (PIREP)** | How the ride felt to the crew | Any pilot with a radio can send one [1] | Subjective, sometimes miles off in position [1] |

WMO notes that the only criterion in the turbulence scale that isn't subjective is the reading of an airborne accelerometer [3]. That's where to start.

## Measuring turbulence in g
A g is a unit of acceleration equal to normal gravity. Flying level in smooth air, you feel 1 g: your normal weight. When the airplane is pushed up, you feel heavier, say 1.3 g; when it drops, lighter, say 0.7 g. Turbulence is usually described by that change, written Δg ("delta g").

An accelerometer is an instrument used to measure acceleration [1]. Airliners carry them, and their flight data recorders log vertical acceleration, which is how accident investigators can say exactly what an airplane went through.

WMO guidance puts the g changes for each level at the airplane's center of gravity [3]:

| Level | Change in g at the center of gravity |
|---|---|
| Light | less than moderate |
| Moderate | 0.5 to 1.0 g |
| Severe | more than 1.0 g |

For scale, US rules require an airliner's structure to carry at least 2.5 g, and at least −1.0 g, without damage [5], with a safety factor of 1.5 on top [6]. You can read what each level feels like in [turbulence levels explained](/guides/turbulence-levels).

### Why the same bump measures differently in different seats
The center of gravity isn't where you sit. When the NTSB estimated load factors along the cabin in one Boeing 737-900ER accident, the rear cabin peaked about 0.2 g higher in magnitude than the center of gravity, while the cockpit generally saw the smallest swings. In an Embraer 190 case, the differences were smaller [1]. So a g reading always belongs to a place: the airplane's center, or your seat.

## EDR: measuring the air, not the airplane
The eddy dissipation rate is a measure of how quickly turbulent energy is being used up in the air, typically shown on a scale [1]. The NTSB compares it to a "sea state": just as wave height doesn't depend on the size of the ship, EDR doesn't depend on the aircraft flying through it [1].

That makes EDR the language of forecasts. Official turbulence guidance is drawn as EDR, technically in units of (m²/s³)^1/3 [7], with values that range between 0 and 1 [2]. ICAO's thresholds are for a medium-sized airliner under typical en-route conditions [2], and the Aviation Weather Center shifts them by aircraft weight. Severe begins at these EDR values (×100) [7]:

| Aircraft class (max takeoff weight) | Severe from |
|---|---|
| Light, under 15,500 lb | 36 |
| Medium, 15,500 to 300,000 lb (e.g., A320, 737) | 44 |
| Heavy, over 300,000 lb (e.g., A330 to A380, 777) | 54 |

**How airliners compute it.** Software on board estimates EDR from the airplane's own sensors and sends it automatically, with an exact position and time, so nobody has to stop and radio a report in the middle of a bump [1]. US airlines use three algorithms; NCAR developed one and commercial companies the other two [1]. IATA endorses NCAR's free, open-source algorithm for its data-sharing platform [4].

**The catch.** Different algorithms aren't guaranteed to give the same value, and much of this data isn't shared publicly [1]. Air traffic controllers told the NTSB they have no way to receive it for their own use [1].

## Pilot reports: measuring by feel
A pilot report rates turbulence on a four-level scale of light, moderate, severe or extreme, judged from how the airplane and the cabin respond [1]. Pilots can add "chop" for rapid, rhythmic bumpiness, and say whether it was occasional, intermittent or continuous [1]. See [what a PIREP is](/guides/pilot-reports-and-sigmets) for how to read them.

PIREPs are priceless because they're everywhere, but they're imprecise. One study found that the location of turbulence in PIREPs differed from automated EDR reports by an average of 25 miles; another found data entry errors in 10% to 20% of turbulence PIREPs [1]. A "moderate" from a small regional jet and a "moderate" from a jumbo jet also describe different air [7]. That's why forecasters value objective EDR so much, and why forecast scores against pilot reports run lower; see [how accurate turbulence forecasts are](/guides/how-accurate-are-turbulence-forecasts).

## Can a phone measure turbulence?
Yes, roughly. A phone's accelerometer measures the sum of two accelerations: gravity and the acceleration given to the device. By tracking the phone's orientation with both the gyroscope and the accelerometer, Apple's Core Motion separates the two [8]. An app can then take the up-and-down part, whichever way the phone is lying, and show the change in g at your seat.

Professionals are moving the same way: the NTSB notes new methods that calculate objective turbulence measures from accelerometers in pilots' tablets rather than installed aircraft sensors [1].

A phone measures your ride, not the airplane's center of gravity, and a hand holding it adds jitter of its own. A good turbulence meter has to handle both.

## How Sorapuff's bump meter measures a bump
Sorapuff's meter works in airplane mode with no network. Here is exactly what it does:

1. **Reads the motion sensors 50 times a second** and keeps only the part of the acceleration that points along gravity, so it works whether the phone lies flat or leans in a seat pocket.
2. **Filters the signal** at 4 Hz so engine buzz and quick taps don't count as turbulence.
3. **Spots hand jitter.** When the phone is being held, the meter pauses and asks you to rest it on the tray table.
4. **Counts a bump** when the change reaches 0.05 g, and ends it once it stays under 0.04 g for half a second. Anything shorter than a tenth of a second is treated as a knock.
5. **Shows a calm needle.** Sensor noise under 0.025 g reads as zero, the needle rises within about a quarter of a second, holds a peak for 0.8 seconds, then settles slowly, so it doesn't twitch.
6. **Labels the ride** light from 0.05 g and moderate from 0.2 g at your seat. These bands are lower than WMO's center-of-gravity criteria above, so read them as a description of your ride, not an official intensity report.
7. **Puts each bump in proportion.** A bump that presses you into your seat is compared with the 1.5 g between normal flight (1 g) and the 2.5 g limit load; a bump that makes you feel lighter, with the 2 g between 1 g and −1.0 g [5]. So a +0.3 g bump used 20% of that margin.

After landing, the Bump Report counts your bumps by level, charts them minute by minute and shows the margin the biggest one used.

## How Sorapuff helps
Numbers calm better than adjectives. Sorapuff's free bump meter shows each bump in g next to what the airplane is built for, and the Bump Report turns "that was awful" into a number: how much of the margin your biggest bump used. It's information, not a safety device: keep your seat belt fastened when seated and follow your crew. For why bumps are rarely dangerous, read [is turbulence dangerous?](/guides/is-turbulence-dangerous)

## FAQ
### How do airplanes measure turbulence?
Airliners measure their own vertical acceleration with accelerometers, and many also compute the eddy dissipation rate (EDR) from their sensors and send it automatically with an exact position and time. Pilots add their own reports on a four-level scale: light, moderate, severe or extreme. Forecasters combine all three, and EDR is the official measure recognized by ICAO and WMO.

### What is a turbulence meter?
A turbulence meter measures how strong bumps are, usually as a change in g from an accelerometer. Airliners record this in their flight data, and phone apps can do it with the phone's own motion sensors. A phone app measures the ride at your seat, which can differ a little from the airplane's center of gravity, so treat its numbers as a good, honest guide.

### Is EDR better than a pilot report?
EDR is objective: it comes from the airplane's sensors, describes the air rather than the airplane, and carries an exact position and time. Pilot reports are subjective and, in one study, were 25 miles off on average. But PIREPs need only a radio, so they come from far more aircraft. Forecasters use both, and value EDR highly.

### How many g is a normal turbulence bump?
WMO guidance puts moderate turbulence at changes of 0.5 to 1.0 g at the airplane's center of gravity, and light turbulence below that. Airliners are built to carry at least 2.5 g without damage, with a 1.5 safety factor on top. A phone at your seat can show you the size of your own bumps.

### Can my phone measure turbulence accurately?
Reasonably, if it rests on a tray table or in a pocket rather than in your hand. Phones separate gravity from motion using the accelerometer and gyroscope together, so an app can show the change in g at your seat. It won't match the airplane's calibrated sensors exactly, and it measures your seat rather than the center of gravity.

## Sources
1. [Preventing Turbulence-Related Injuries in Air Carrier Operations Conducted Under Title 14 CFR Part 121, Safety Research Report SS-21/01 (2021), NTSB](https://www.ntsb.gov/safety/safety-studies/Documents/SS2101.pdf)
2. [New 0.25 degree WAFS Hazard Data, training material (November 2020), ICAO](https://www.icao.int/sites/default/files/METP/Documents/Nov-2020-New-WAFS-Hazard-data-training-material.pdf)
3. [Aviation Hazards: Turbulence and Wind Shear, World Meteorological Organization](https://community.wmo.int/node/36996)
4. [Turbulence Aware for airlines, International Air Transport Association (IATA)](https://www.iata.org/en/services/data/safety/turbulence-platform/airlines/)
5. [14 CFR § 25.337, Limit maneuvering load factors, Legal Information Institute (Cornell Law School)](https://www.law.cornell.edu/cfr/text/14/25.337)
6. [14 CFR § 25.303, Factor of safety, Legal Information Institute (Cornell Law School)](https://www.law.cornell.edu/cfr/text/14/25.303)
7. [Graphical Forecasts for Aviation help: Turbulence, Aviation Weather Center (NOAA)](https://aviationweather.gov/gfa/help/?page=turb)
8. [CMDeviceMotion, Core Motion documentation, Apple Developer](https://developer.apple.com/documentation/coremotion/cmdevicemotion)

Updated November 13, 2026 · https://sorapuff.app/guides/how-is-turbulence-measured

## Related guides

- [Turbulence Levels Explained: Light to Severe, in g](https://sorapuff.app/guides/turbulence-levels): Light, moderate, severe and extreme turbulence as the FAA and ICAO define them, what each feels like, the g forces involved and the 2.5 g planes carry.
- [What Is a PIREP? What Is a SIGMET? Explained Simply](https://sorapuff.app/guides/pilot-reports-and-sigmets): A PIREP is a pilot's report of the weather met in flight; a SIGMET is an official hazard warning. Learn to read both and what they mean for your flight.
- [Is Turbulence Dangerous? What the Safety Data Says](https://sorapuff.app/guides/is-turbulence-dangerous): Turbulence is uncomfortable but rarely dangerous for a belted passenger. See the NTSB data, the 2.5 g airliners are built for, and how to stay safe.
- [Turbulence Forecast for Your Flight: How It Works](https://sorapuff.app/guides/turbulence-forecast): A turbulence forecast shows where bumps are likely on your route, built from wind data, storm warnings and pilot reports. How to read one, and its limits.