This app measures magnetic field and display the data as graph or map in units of nanotesla (nT; one nanotesla equals 10^−9 tesla). Displays Z (downward component), H (horizontal intensity) and F (total intensity) of the local magnetic field vector. Data processing reduces the noise in the data to about 1% of the actual magnetic field. We rotate the magnetic data from the phone’s orientation to the real-world coordinates. Use it for recording magnetic data at a location or over an area. Export your data as a CSV file. Optionally, enable background reporting to help NOAA scientists understand more about the Earth’s magnetic field!

The new addition, Compass tab features a compass dial and level bubble, true North, local magnetic North, magnetic declination from World Magnetic Model, compass accuracy and current solar magnetic disturbance!

Use CrowdMag app as an offline magnetic calculator. Quickly get magnetic variation at remote sites or ships. Calculator gives magnetic variation (declination), dip angle, total field and other magnetic field components for date and location based on the latest World Magnetic Model (WMM2015). The model is developed primarily using data from ESA’s SWARM satellites and it accurately predicts the main magnetic field anywhere on the globe. It also provides the uncertainty and the time change of the modeled magnetic field.

CrowdMag Features:

- Customize recording frequency and location accuracy
- Interactive Google Map showing your magnetic data
- Graph your data as time series
- Check the quality of the data by comparing with WMM
- Export your data as a CSV file
- Enable/disable background reporting
- Clear stored data on your phone
- Optionally share your data with NOAA
- See crowdsourced magnetic data from other users

Compass Features:
-Compass dial
-Level Bubble
-True North
-Local Magnetic North
-Compass accuracy
-Current solar magnetic disturbance

Magnetic Calculator:

- Uses the most recent model (WMM2015)
- Compute Declination, Dip and Total Field and other components for given date and location (2014-2019)
- Autolocate your latitude/longitude
- Uncertainty
- Compass rose on a map
- Export data via email, Google Drive and other options

Visit to see crowdsourced magnetic data. Developers, let us know if you want to contribute magnetic data from your app to NOAA. Keywords: Magnetic Variation, World Magnetic Model, geomagnetism, crowdsourcing, sensor, navigation, magnetic, WMM, citizen, science, NOAA, calculator, compass.

Note that continued use of GPS running in the background can dramatically decrease battery life.

What’s New

Version 1.7.5

We updated World Magnetic Model to the latest version, WMM2015v2. For more information, visit

Ratings and Reviews

3.8 out of 5
10 Ratings

10 Ratings

Jason somthing ,

Zero effort to contribute to cool research

Just open the app and set how often you want to send them data. These types of apps are a great way to harness the power of your iPhone and with no effort make a positive contribution. Nice touch adding achievements for contributions and locations. The magnetic information is interesting to see but that’s about it. Just know your contribution will help other researchers.

KB Traveler ,

Excellent Info

I travel the world for a living. Knowing the correct Mag Variation has come in handy. The latest version includes an excellent compass which gives both True and Magnetic North. It is nice to be able to contribute information for this program. I find that it doesn't effect my battery usage that much.

ken23410 ,

1.7.5 cannot take location from at least some iPhones

iPhone 5s 32GB iOS 12.1.4 App never acquires location data from the phone and therefore never records data. I reported this to NOAA just last week. It would be interesting to hear from people using newer, more capable iPhones, although no mention is made of any limitations on older phones.

Makes a very nice compass app though.


National Oceanic and Atmospheric Administration
12.3 MB

Requires iOS 10.0 or later. Compatible with iPhone, iPad, and iPod touch.



Age Rating
Rated 4+
This app may use your location even when it isn't open, which can decrease battery life.
© National Oceanic and Atmospheric Administration


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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