Odds are most commonly expressed as ratios, When you convert them into percentage,you can do like this.
If odds are stated as an Number A to Number B, The Probability or Percentage is given as P = B / (A + B). The Result percent chance is calculated as P x 100.
This calculator commonly used as chance of success then the probability of success and so on.
For example: Number A is 3, Number B is 2, Result: 3 to 2 Odds Percentage is P = 2/(3+2) % = 40 %.