def colourBarMinorAxisSize(fontSize):
    """Calculates a good size for the minor axis of a colour bar.

    The minor axis is the axis perpendicular to the colour bar axis.

    :arg fontSize: Font size of colour bar labels, in points.
    """

    # Figure out the font size in pixels
    # (font points are 1/72th of an inch,
    # and we're using inside knowledge
    # that the colourbarbitmap module
    # uses 96 dpi, and a padding of 6
    # pixels).
    fontSize = fontSize
    fontSize = 6 + 96 * fontSize / 72.

    # Fix the minor axis of the colour bar,
    # according to the font size, and a
    # constant size for the colour bar
    return round(2 * fontSize + 40)