Gravitational Force Calculator
Newton's universal gravitation. Scientific notation like 5.97e24 works.
The law
F = G × m₁m₂ / r²
G is 6.674 × 10⁻¹¹, absurdly small, which is why gravity only matters when at least one mass is planet-sized. Earth and Moon with the defaults pull on each other with about 2 × 10²⁰ N.
The inverse square
Double the distance, quarter the force. It never reaches zero: every mass tugs every other across the universe, just diminishingly. Two people a meter apart attract with about 3 × 10⁻⁷ N, hopelessly drowned out by everything else.