a new year's stretch

we used to do these as kids.

here is your new year's stretch.

Burning rope

There are two lengths of rope.
Each one can burn in exactly one hour.
They are not necessarily of the same length or width as each other.
They also are not of uniform width (may be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour.

By burning the ropes, how do you measure exactly 45 minutes worth of time?

let me know when you have an answer and try not to google it too quick.