Below is a chart of biking paces for a variety of common triathlon distances.
These are direct conversions not predictions.
Use the chart to look up your triathlon race distance and the average pace you expect to cover the distance in. With the race distance and estimated pace you can find how long it will take to finish the bike leg.
For example, if you were to average 18 mph on the bike leg for an Ironman race you would finish in a time of roughly 6 hour, 13 minutes and 20 seconds.
The following graphic can be used to get a sense of how long the bike portion of different race distances compares. This is a good one to keep in mind if you are ramping up for Ironman.