how to know print size after page break

Question

I use iframe and height fit use iframeResizer and iframe cotent height is variable.

Problem is that print page content is cutting because i fix iframe height use iframeResizer but page break make diff iframe content height.

then I have some questions.

1. how to know height after page break? I try to solve problem get height and change iframe height but don't know.

2. how to solve that?

3. when page break working? I check window.onbeforeprint use iframeResize but not change height.