def calculate_capacity(versions):
    """
    Calculate total capacity based on given versions.

    Args:
        versions (list): List of tuples containing version, size, speed, and IOPS.

    Returns:
        float: Total capacity in GB.
    """
    total_size = sum(version[1] for version in versions)
    return round(total_size / 1024 ** 3, 2)

# Example usage
versions = [('v5_1768236144', 108217.11959687909, 721, 15009.3),
            ('v5_1768235312', 89435.63603047856, 734, 12184.7),
            ('v5_1768235983', 98379.19963352643, 987, 9967.5)]

print(calculate_capacity(versions))