Ever wanted to know your chance of catching Pokemon? Enter in the Pokemon and Pokeball you wish to use. See the catch chance and level of the Pokemon for every ring colour by moving the colour slider. Min and max catch chances are shown either side of the slider. Gen 2 catch chances are still unknown. Detailed explanation below.
On a difficult Pokemon like a high level Charizard, fully empowering your throws can increase catch chance over 15 times compared to a basic Pokeball.
Catch chance increases with Pokeball Type, Curve Balls, Razzberries, Type Medals, and the size of the coloured ring when you through the ball (smaller is better). Each of these affects has its own multiplier (shown immediately above) and they all multiply together to acheive the Total Multiplier.
Higher level Pokemon are more difficult to catch and some species are just more difficult to catch because they have a lower "base catch rate", see all Pokemon and their base rates at Pokemon Stats.
If you don't capture the Pokemon, each species has a chance to flee.
The catch chance benefit of throwing a curve ball is better than throwing a great ball and almost as good as an ultra ball, always curve ball.
The catch chance benefit of throwing the ball when the circle size is at its minimum is as good as throwing an ultra ball, both will about double your catch chance and together, quadruple it.
If it's just a Pidgey or Weedle and your circle is already pretty green, don't worry about its size. Go for an easy 10-50XP with a Nice/Great throw since you don't need a big catch chance boost from a small circle.
Play around with the calculator and come to your own conclusions :)
The colour of the rings in this tool match exactly the colours in game thanks to some stunning research by u/dondon151.
Ring size calculation is still tentative but accurate to a reasonably large sample size thanks to a lot of work by u/RhyniD.
The science on catch chance isn't 100% complete, but for what we know right now, this tool is accurate:
Final Chance = 1 - ( 1 - Level Chance) ^ (BallMulti * CurveMulti * BerryMulti * SizeMulti * MedalMulti)
Level Chance = 50% / CPMulti(Level) * Base Species Chance
The SizeMulti increase from 1 to 2 as the coloured ring's size decreases relative to the grey ring.
The CurveMulti increase from 1 to 1.7 if the trainer curves the throw.
The BallMulti increases from 1 -> 1.5 -> 2 as the trainer uses better balls.
The BerryMulti increases from 1 -> 1.5 if the trainer uses RazzBerries.