The smallest unit in physics is the planet length. wr need to know constant (h) the speed of light (c) and newton's gravitational constant ( g). find the planck length.

Yes, that's right.  It's the 'Planck' length, not the 'Planet' length.

You could easily find these with a web search.  But in gratitude
for the bountiful 5 points, I've saved you the trouble. 
AND guess what !   By doing that, I learned something, and
you didn't.

Speed of light (c):                 299,792,458 meters per second

Gravitational constant (G):   6.67 x 10⁻¹¹  newton-meter²/kilogram²

Planck's Konstant (h):           6.63 x 10⁻³⁴ joule-second

Planck Length:                      1.6 x 10⁻³⁵ meter
                                            (about 10⁻²⁰ the size of a proton)

Planck Time:                          10⁻⁴³ second
                                             (about the time it takes to travel
                                              a Planck Length at the speed of light)