First find the diameter of each.
Jupiter’s diameter is 86,881 mi.
Earth’s diameter is 7,917.5 mi.
Then divide those two.
Rounded, Jupiter is 11 times larger.
unrounded: 10.9732870224186927691821913482791285127
Finding out how large something is compared to something can be done by dividing.
For example I have two dogs. One dog is 3 feet tall. The other is 2 feet tall. How much taller is dog one? Dog one is 1.5 times larger because 3/2 = 1.5 AND 2 x 1.5 = 3.
So for this case multiplying Earth’s diameter by 10.9732870224186927691821913482791285127 will give you Jupiter’s diameter.