Obviously, most of the bookmakers have settings where you can choose the odds format understandable for you. In worst case scenario you can Google it and odds converter will sort it out for you in seconds.
But it is not so difficult to calculate it yourself. Most common odds formats are decimal, fractional, American and couple of Asian formats.
Decimal – it is the most common format for Europeans. And easiest to understand (at least for Europeans).
Stake x odds = payout (100 x 1.8 = 180)
Payout – stake = profit (180 – 100 = 80)
Fractional – the oldest odds style in the world, at least 500 years old. Most common in the United Kingdom and Ireland. Odds are represented as fractions (for example 6/4 – “six to four”). The first number represents profit made compared to the stake placed. So, in our example, you will make 6 euros profit, if you place 4 euros.
To recalculate to decimal odds you can use following formula (divide fractional odds and just add 1):
6/4 + 1 = 1.5 + 1 = 2.5
American – obviously mostly used in USA. American odds are positive (+100, +250, +650 and etc.) and negative (-100, -500, -1000 and etc.).
Calculation for positive odds:
Decimal odds = (US odds/100) + 1
Example for 500: (500/100) + 1 = 6.0
In other words, if you see odds of 500, it shows the actual profit for every 100 USD/€/£ you bet. Odds of 350, would equal to 4.5 at decimal format (450 – 100 staked = 350 profit).
Positive odds equals decimal odds from 2.0 and higher.
Calculation for negative odds:
Decimal odds = (100/US odds) + 1
Example for -250: (100/250) + 1 = 1.4 (do not use (-) in formula, just number)
In other words, odds with minus sign shows the amount you need to bet to win 100 USD/€/£. You would need to place 250 USD/€/£ to win 100 USD/€/£ at odds of -250.
Negative odds equals decimal odds from 1.01 to 1.99.
Most common Asian odds formats are Hong Kong, Indonesian and Malay.