Does watching videos while connected to Wi-Fi use data?

Sometimes I go places and forget to bring my tablet so all I have with me is my iPhone 5s but I'm scared that I will waste data if I watch videos. Will I use data if I watch videos while I'm connected to Wi-Fi?

Lol no becuz your using Wi-Fi

No, but just to be doubly sure, go to SETTINGS then CELLULAR, then turn the CELLULAR DATA off (slide to no green)

If you are watching video online, then of course it will use data!

If you are watching offline from a file, the video it self won't use data, BUT! Background applications like messaging apps, the video player you are using, all other apps checking for updates, your operating system and etc will use data! Either turn Airplane Mode on or turn off Data Exchange or Wi-Fi or Cellular Data or anything like that to prevent ANY data usage.

If you are only concerned about Cellular Data, turning it off will prevent any SIM-based (Cellular) data usage.

No it doesn't.

Your question wasn't specific enough. I think you meant to say, "If I use Wi-Fi to watch movies on my phone, am I using up my phone's data?"

Answer: No. You're using up your home's data.

It shouldn't. Turn off the iPhone 5s data settings and just confirm you are receiving the video via the Wi-Fi.