I am sponsoring a competition for high school students. Video entries can be at most 3 minutes long? What size should I make the Upload field?

What size should I make the Upload field to be able to accept a 3 minute vide from applicants

That will really depend on what kind of a cameras your users will have, and how big the resolution they will use for shooting their videos. Teenagers will usually have phones with rather good cameras that generate video in 720p HD video or higher.

According to Apple, who provide such notes for their mobile devices, a 720p video at 30 frames per second will take about 60MB per minute - and this is the lowest video resolution and frame rate for latest phones.

A little larger 1080p video at 30 frames per second needs roughly about 130MB per minute.

Given the above, you may need to allow even up to 300MB of upload per form if your students will be shooting their videos with new phones, with 1080p resolution. If that is too much, you can also inform them on the form through that the video must not be longer then 3 minutes or larger than 150 MB, and instruct them not to shoot the video in formats larger than 720p.

I hope this helps.

Great...Thanks