https://cs.m.wikipedia.org/wiki/Starship_(raketa)
And it makes sense if you think about it - as you scale up, the ammount of fuel you can carry goes up roghly by cube while structure mass, forming a shell effectively arround the fuel, goes up by square of size of the rocket.
Similar things for air resistance - as you scale up yuour rocket the front part creating the most drag will scale more slowly than the volume of the rocket that goes to fuel, payload and structure.
No wonder Starship is already at 9 meters of width and 18 m has been mentioned as a possible future upgrade. Its already bigger than the massive 66+ meter high medieval watchtower in my home town yet it can fly to sub orbital speeds without its first stage booster (which is even bigger)!