The ForeFlight Mobile app alone (with no data downloaded) uses about 350 MB of space once installed on your device. The app plus minimum required downloads (Airport Database, Business Directory, North American Obstacles, Terrain Map, and World Map) but no charts or plates requires 1.5 GB of space.
For use in flight, ForeFlight Mobile can store airport diagrams, terminal procedures, and navigation charts for the United States and Canada. More storage space will be consumed once you start downloading charts, maps, documents, and more. The Downloads page (More button > Downloads) lists the approximate size of each download so you can estimate how much space is required for your selections.
Download sizes can vary greatly, depending upon your selections. If you want to download everything available, plan on the USA lower 48 States and Hawaii taking about 15.5 GB and Alaska taking up about 4.5 GB of storage space. Canada will require about 11 GB for all available downloads. Downloads for the Caribbean, Mexico, and Central America take up about 1.9 GB.
If you do not plan on downloading all of the USA or Canada, a good rule of thumb for the USA is that each state requires, on average, 320 MB to download all items (i.e.: Terminal Procedures, IFR and VFR charts, WAC charts, High Resolution Terrain, Synthetic Vision, etc). Larger states like Texas or California will require more space, and Alaska alone takes up around 4.5 GB of space. Canada requires, on average, 850 MB per Province or Territory with all available items selected. Larger areas like Nunavut will take up about 3GB of space.
A few items displayed on the Downloads page display a compressed file size. This means the actual size, when de-compressed (un-zipped), will be larger when the file is installed. The compressed items are as follows:
- United States (lower 48) high resolution terrain is a 242 MB download and takes up 1 GB on disk.
- Mexico/Caribbean/Central America high resolution terrain is a 96 MB download and takes up 737MB on disk.
- Canada high resolution terrain is a 334 MB download and takes up 1.4 GB on disk.
- Alaska high resolution terrain is a 56 MB download and takes up 947 MB on disk.
- Worldwide low-resolution terrain map is a 61 MB download and takes up 320 MB on disk.
- Airport Database is a 133 MB download and takes up 650 MB on disk.
Approaching a chart cycle changeover date, pilots usually download the data update a few days before the 28 day changeover. The Delta Downloads feature significantly reduces the size of the next data cycle download because only the changed items are downloaded at each new data cycle.
With Delta Downloads, new data cycle downloads will typically require only an additional 10-20% of the currently used space. For example in an early 2016 download, downloading 49 states + 4 Canadian provinces required 15.6 GB of space during the data cycle, but only 17.1 GB of space during the change over, a difference of just 1.5 GB.
Once the new data cycle is effective, the old data will automatically be deleted after ForeFlight Mobile is opened. This automatic deletion process spans several minutes so as not to impact the performance of the app. All expired data can be immediately deleted by tapping the Delete button on the Downloads page and choosing "Delete Expired."
Downloading all of the documents and handbooks available in the United States subscription requires almost 1 GB of space.