How do we measure the size and mass of other planets?

Question

I can find info on Earth but not others

Answer 1

For any planet with a moon, the planet's mass can be approximated by GmM/r² = mv²/r = mrω² = mr(2π/P)², where G is the gravitational constant, m the mass of the moon, M the mass of the planet, r the distance between planet and moon, and P the period of the moon. The mass of the moon cancels out, leaving
M = r³(2π/P)²/G

The masses of moonless planets have to be determined by Perturbation Theory, the effect of one planet's orbit on the orbits of other planets.

The diameter of another celestial object can be estimated by multiplying the angle subtended by the object by its distance from us. A closer estimate is obtained by
d/2 = Dsin(α/2)
where d is the diameter, D is distance to the object, and α is the subtended angle.

Answer 2

The speed of their orbit around the sun (approximately circular) can tell us how far away they are, and if we know the distance and angular diameter (how big they appear) then simple trig tells us how big they are. Newton's laws of gravity can tell us the mass for a body in orbit (GMm/r^2) where G is the gravitational constant, M is the mass of the Sun, m is the mass of the planet, and r is the radius of the planet's orbit - which we got from the velocity.