def number_from_label(label):
    """
    Coverts a letter label (e.g. plate row label) into a number.

    :param label: The label you want to convert.
    :type label: :class:`string`
    :return: The number corresponding to that label (:class:`int`).
    :Note: This function returns a number, not an index. If you want to
           work with indices, make sure to decrease the number by one
           before using it.
    """
    row_number = 0
    row_label_chars = list(label.upper())
    for i, c in enumerate(reversed(row_label_chars)):
        colnum = ord(c) - 64
        row_number += colnum * pow(26, i)
    return row_number