How to know if your height is O.K. for a grand piano?

[scherzando23]

I have a competition coming up and for the first time EVER this one will use a grand piano because there will be an audience and will be happening in a really big auditorium. But I have a question, how can I know if my height is okay for the grand piano and my feet will touch the pedals? I dont know my exact height to be honest, but my estimation is about 4 1/2- 5 feet in height. Is that a good height for a grand, where I wont need the extension pedals? What if the bench is those fluffy ones that have knobs at the end of each side that makes the bench higher or lower?

Any tips or suggestions please.