Convert units to GB

def _convert_size(self, size_str):
        """Convert units to GB"""
        suffix = size_str[-1]
        if suffix == 'K':
            multiplier = 1.0 / (1024.0 * 1024.0)
        elif suffix == 'M':
            multiplier = 1.0 / 1024.0
        elif suffix == 'T':
            multiplier = 1024.0
        else:
            multiplier = 1

        try:
            val = float(size_str.split(' ')[0])
            return val * multiplier
        except ValueError:
            return 0.0