CrowdMag is a tool that measures the local magnetic field using your smartphone! The app displays the data as a graph or a map in units of nanotesla (nT; one nanotesla equals 10^−9 Tesla). The local magnetic field components measured by CrowdMag are the Z (downward component), H (horizontal intensity), and F (total intensity). Use CrowdMag for measuring magnetic data during your outdoor adventures or to conduct your own homegrown science! To perform your own experiments or analyze your observations, export your data as a CSV file. Optionally, your magnetic data may be shared with NOAA to help scientists understand more about Earth’s magnetic field!

What is new!

CrowdMag is going active! When you go out for a walk, run, or other outdoor activities, use CrowdMag to measure the magnetic data along your path and save the data as a “magtivity”. Save, list, export or delete magtivities to create a complete magnetic field map of your area. We particularly encourage you to share your magtivities with our research group at NOAA and to have multiple magtivities along the same path so that we can stack the data to reduce the noise.

Getting a new phone? Don’t worry! You can now export a backup of your CrowdMag and save it on your computer. If you have to reset your phone, or switch to a new phone, you can now import your backup and continue using CrowdMag without losing your status for data contributed, areas covered, or magtivities completed.

CrowdMag’s magnetic calculator provides magnetic variation (declination), the magnetic field’s dip angle, total magnetic field and other magnetic field components (as well as their associated uncertainties) based on the latest World Magnetic Model (WMM2020).

CrowdMag Features:

- Create your own magnetic activity (magtivity)
- Customize recording frequency and location accuracy
- Interactive Google Map provides a map of your magnetic data
- Graph your data as a time series line chart
- Check the quality of the data by comparing it with the WMM
- Export your data as a CSV file
- Clear stored data on your phone
- Optionally share your data with NOAA
- See generalized crowdsourced magnetic data from other users
- Live magnetic compass
- Current solar magnetic disturbance
- Expected magnetic field calculator
- Uses the most recent magnetic field model (WMM2020)
- Export data via email, Google Drive and other options
- Export CrowdMag backup to save your contributions' status and data
- Import CrowdMag backup (works across different phone platforms)

Visit to see crowdsourced magnetic data.

What’s New

Version 1.8.5

Facebook and twitter share options for mystatus were added back in

Ratings and Reviews

4.1 out of 5
16 Ratings

16 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.

Adam Woodworth ,


I am a photographer and I use this app to find the magnetic declination of my current location so that I can correct my compass readings to true north to match with the true north bearings given in some landscape photography planning apps.

App Privacy

The developer, National Oceanic and Atmospheric Administration, has not provided details about its privacy practices and handling of data to Apple. For more information, see the developer’s privacy policy.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

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

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