In detail
Disney+ streams most of its catalogue in Full HD and a large share of its films and originals in 4K Ultra HD with HDR10 or Dolby Vision. The app picks a quality automatically based on your connection, device and subscription, so the data it uses can vary a lot between a phone on mobile data and a 4K TV on fibre.
As a rule of thumb, standard definition uses around 0.7 GB per hour, HD about 3 GB and 4K up to about 7 GB per hour. A family movie night with a two-hour film in 4K therefore uses roughly 14 GB — more than many small mobile plans include for a whole month. Disney+ recommends a connection of around 25 Mbps for 4K.
Only the higher Disney+ tiers include 4K and Dolby Atmos; the cheaper plans with ads are limited to Full HD in many countries. If you mainly watch on a tablet or phone, Full HD is visually almost identical to 4K and uses about half the data.
To save mobile data, open the app settings and choose 'Save Data' under cellular data usage, which caps streams at a fraction of the HD rate. Downloading episodes over Wi-Fi before a trip uses your home connection instead of your mobile allowance, and downloads can also be set to a lower quality to save storage.
The calculator above is pre-filled with two hours of Disney+ in 4K. Add other services your household watches and the number of screens streaming at once to see your monthly total and the data plan you need.