How does HD content look on a UHD screen?

[gautamgr8]

I want to purchase a new monitor for my PC & I'm thinking about a 4K monitor just to be future proof.
But most of my content & my work would only be 1080p.

Would 1080p content look bad on a 4k display?
Can anyone tell me how HD content looks on a UHD screen?

I also plan on connecting my PS4 to the same 4K monitor and play leisurely. Will console games look blurry on UHD?

*
1) Cost of the monitor and my PC graphics card capability is not a concern (EVGA GTX970).
2) I am not a PC gamer. I use my computer only for work.

Please help...!

 

[i7Baby]

If you put 1080p on a big screen, it looks grainy.