Around 100% for anyone using the normal Tor browser bundle.
Tor is designed to hide who you are talking to, not the fact that you are using Tor. IPs and other metadata about normal Tor relays are published publicly by the network and are used by the client to build circuits through the network.
There is a special form of hidden entry node called a bridge that is designed for use in censorship-happy countries like China, but using them is a manual process that isn't the default. Traffic through bridges is a very low percentage of overall Tor usage.
Tor is designed to hide who you are talking to, not the fact that you are using Tor. IPs and other metadata about normal Tor relays are published publicly by the network and are used by the client to build circuits through the network.
There is a special form of hidden entry node called a bridge that is designed for use in censorship-happy countries like China, but using them is a manual process that isn't the default. Traffic through bridges is a very low percentage of overall Tor usage.