The 100 RATINGS.

{18-49 demo/viewers in millions}

Season 1
1-01: Pilot {0.9/2.73}
1-02: Earth Skills {0.7/2.27}
1-03: Earth Kills {0.6/1.90}
1-04: Murphy's Law {0.5/1.69}
1-05: Twilight’s Last Gleaming {0.5/1.80}
1-06: His Sister’s Keeper {0.6/1.97}
1-07: Contents Under Pressure {0.6/1.88}
1-08: Day Trip {0.6/1.64}
1-09: Unity Day {0.6/1.73}
1-10: I Am Become Death {0.6/1.97}
1-11: The Calm {0.6/1.73}
1-12: We Are Grounders Pt.1 {0.6/1.58}
1-13: We Are Grounders Pt.2 {0.5/1.65}

Season 2
2-01: The 48 {0.5/1.59}
2-02: Inclement Weather {0.5/1.48}
2-03: Reapercussions {0.5/1.68}
2-04: Many Happy Returns {0.5/1.75}
2-05: Human Trials {0.6/1.64}
2-06: Fog of War {0.6/1.86}
2-07: Long into the Abyss {0.6/1.62}
2-08: Spacewalker {0.5/1.40}
2-09: Remember Me {0.5/1.48}
2-10: Survival of the Fittest {0.5/1.53}
2-11: Coup de Grace {0.5/1.51}
2-12: Rubicon {0.5/1.36}
2-13: Resurrection {0.5/1.42}
2-14: Bodyguard of Lies {0.5/1.545}
2-15: Blood Must Have Blood Part 1 {0.5/1.494}
2-16: Blood Must Have Blood Part 2 {0.4/1.341}


Season 3
3-01: Wanheda: Part 1 {0.7/1.881}
3-02: Wanheda: Part 2 {0.6/1.631}
3-03: Ye Who Enter Here {0.6/1.567]
3-04: Watch the Thrones {0.5/1.322}
3-05: Hakeldama {0.5/1.356}
3-06: Bitter Harvest {0.6/1.407}
3-07: Thirteen {0.5/1.39}
3-08: Terms and Conditions {0.4/1.204}
3-09: Stealing Fire {0.45/1.231}
3-10: Fallen {0.4/1.125}
3-11: Nevermore {0.4/1.083}
3-12: Demons {0.4/1.154}
3-13: Join or Die {0.4/1.269}
3-14: Red Sky at Morning {0.4/1.311}
3-15: Perverse Instantiation: Part 1 {0.4/1.170}
3-16: Perverse Instantiation: Part 2 {0.5/1.29}


Season 4
4-01: Echoes {0.4/1.212}
4-02: Heavy Lies the Crown {0.4/1.013}
4-03: The Four Horsemen {0.4/1.045}
4-04: A Lie Guarded {0.4/0.998}
4-05: The Tinder Box {0.4/1.023}
4-06: We Will Rise {0.3/0.982}
4-07: Gimme Shelter {0.3/0.895}
4-08: God Complex {0.3/0.969}
4-09: DNR {0.3/0.812}
4-10: Die All, Die Merrily {0.3/0.854}
4-11: The Other Side {0.3/0.861}
4-12: The Chosen {0.3/0.830}
4-13: Praimfaya {0.3/0.914}

reddit user r/kaktusz has a great ratings breakdown here
also another source here