How to get matplotlib figure size

import matplotlib.plt
fig = plt.figure()
size = fig.get_size_inches()*fig.dpi # size in pixels

To do it for the current figure,

fig = plt.gcf()
size = fig.get_size_inches()*fig.dpi # size in pixels

You can get the same info by doing:

bbox = fig.get_window_extent().transformed(fig.dpi_scale_trans.inverted())
width, height = bbox.width*fig.dpi, bbox.height*fig.dpi