How do I estimate the traffic of particular web site?

Hello,
I need to estimate traffic of the web sites on which I plan to place my banners.
It was Alexa ranking.
Which tools are used today?

You can use SEMRush or Ubersuggest that can give you approximate idea about the traffic of any particular website. Please note that such estimates are not 100% accurate but they only refer a range of traffic that website is getting.

Similarweb is often more accurate than Ahrefs or Semrush

You can use similarweb, ahrefs, semrush tool.

First better already knew a site which you get the real traffic numbers, then check its ranking on above tools, then map your competitor's ranking to its real traffics. Though the result is not very reliable in some cases, e.g. a website got a lot of traffics from social media, etc.

I suggest Ahrefs or SEMRush check the traffic metrics. You can check the links of the particular website and sort out them to check the traffic source for that list of sites too.

Ahref and semrush are two tools you can use for this. If you do not want to buy these foe checking, you can ask someone on BHW to check for you, it can be done in few seconds.

Don't use ahrefs or semrush for traffic estimates... use similarweb

I would ask the website owner to provide me with the measuring tool he uses to make sure that the ad campaign is profitable.

Guessing has no place in paid advertising.

Similarweb is the most accurate.

Many thanks.
I have now my list and I will learn it.

Similarweb and Ahref's can do the intense behavioral view of where the traffic is flowing and dropping. Again, configuring the website with Google Analytics and Tag Manager signals can give the exact results.

Let's say, Ahref pulls details from the google search console and optimizes it in a different data representation.

Ahref is accurate in organic traffic

Ahref is always ultimate. But You can use a similar web and semrush buddy.

Semrush can give you approximate data related to this.