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These numbers sound about right to me. In the UK, with ~2 million engaged viewers, we see around a 1-2% conversion when a URL is mentioned and shown on the screen (off the top of my head 20,000 users in a 30 sec period would be a fair average), typically 3-6% conversion over the course of a 1 hour show.

The important thing is for the website to exist and be online within the 5 minutes of the URL being displayed.

If the presenter reads a URL and also explains some activity that can be done on the site, you can get anywhere from 2x to 40x the traffic that just showing or just saying the URL will create, it depends on the activity and also which presenter is reading out the URL.

Displaying the URL alongside a screenshot or a video of website will net you 4+ times the number of visitors that a simple piece of text displayed or read, but not as much as a presenter telling viewers to go to the website.

A broadcast on a delayed +1 channel gets you 10% of the above traffic.