Kind of. All spheres and circles have a diameter, which is the length of a line passing through the center of the sphere. The only problem is that most planets aren't 100% perfect spheres, so the diameter could be different depending on where you start measuring from.
Mercury
The planet Uranus.
To calculate the diameter of a planet, you can use the formula for the diameter based on the planet's radius: Diameter = 2 × Radius. If you have the planet’s circumference, you can also calculate the diameter using the formula: Diameter = Circumference / π (where π is approximately 3.14). Additionally, if you have access to images or data from space missions, you can use measurements of the planet's shadow or transit across a star to estimate its size.
The planet you are referring to is Jupiter, which has a diameter of approximately 86,881 miles. Mercury has a diameter of about 3,032 miles, Venus has a diameter of about 7,521 miles, Earth has a diameter of about 7,917 miles, and Mars has a diameter of about 4,212 miles.
Jupiter is the largest with the largest diameter.
the Jupiter diameter is 142,984km
None. The closest case that we have in our solar system that of Charon, Pluto's largest moon, which about roughly half the diameter of Pluto. Since Pluto is no longer considered a planet the largest moon-planet size ratio is that of our own moon, which is about one quarter the diameter of Earth.
Uranus is third largest. Diameter = 51115km, about 8 times that of Earths diameter.
Mercury is the smallest planet, so there isn't one with half the diameter.
The largest planet in the solar system is Jupiter, with a diameter 11.209 times that of the Earth
Mercury is the only planet in our solar system that is less than 3000km in diameter, with a diameter of about 4879 km.
To qualify as a planet, a body has to be approximately spherical (achieving hydrostatic equilibrium under its own gravity), it has to orbit the sun and it has to have cleared its orbit of all other objects - so that at that distance from the sun, there are no other sizable bodies. Theres no set size, but to achieve an approximately spherical shape under its own gravity, a planet would have to be at least around 500-600 miles in diameter.