60 Hz in the US. 50 Hz in some other countries.
However, Refresh Rates normally applies to your TV. Meaning, the number of times-per-second a screen updates its image. Times-per-second is measured as Frequency and expressed as Hertz (Hz), such as 60 Hz.
Anything above 120 Hz is marketing hype. Bigger number, better picture...right? No.
You need to research the Panel Refresh Rate. Meaning, at what frequency does the panel of a TV actually refresh its image. Don't get duped by modifiers, such as "TruMotion" or "Image Motion." These are the marketing hypes.
The Refresh Rates for HDTV sets are not above 120 Hz, despite what their numbers claim, and many are just 60 Hz.
Also, if you'll only watch TV programs, you don't need a 4K TV. No television network broadcasts anything above 720p and 1080i. The only 4K content available is through streaming services or a few UHD Blu-ray players.
Moreover, the standards for UHD...such as High Dynamic Range, a wider color palette and higher bit rates...are still evolving. Meaning, whatever 4K set you buy today may not be fully future proof, such as higher capacity HDMI ports.