You need to take into account the system files. I wish Apple had not sold a 16Gb model of iPad. This is only really suitable for basic operations. 32Gb is more sensible but for reasons unknown Apple have omitted this version on the new iPad and keep the 16Gb version. It can be difficult, if not impossible, to update the OS through wifi on the 16gb version and iTunes has to be used.
Surface Pro (2017) vs Surface Pro 4