American to decimal to implied probability — type in any box and the other two follow.
Every price is a probability wearing a costume. -110 means the book is charging you as if the outcome happens 52.4% of the time; +250 implies about 28.6%. Converting odds into a percentage is the fastest way to ask the only question that matters: does this happen more often than the price says?
One catch — implied probabilities on both sides of a game add up to more than 100%. The excess is the book's margin. To see prices with that margin stripped out, every game on today's board shows the no-vig win chance next to the posted price.