How much storage does iOS 12 require?

I have a iPad air 1st gen 16GB (model A1474).

I want to install iOS 12 on it, but I am not sure if 16GB is sufficient storage.

Right now I have iOS 9.3.5, and I can't see how much does the iOS itself takes, but I have enough storage for many apps and music.

Does anyone know how much storage does the iOS 12 takes on the iPad? I am afraid I will not have any storage left for apps and data.

After installing iOS 12, and then restoring my device to factory default I see that the iOS take 5.1 GB.

To me it seems like iOS 12 is consuming up to 7 GB of the disk on a relatively clean install.

Below are my details (same iPad model as original poster with iOS 12.4.8):

After doing a factory reset and importing a very modest iCloud backup:

After doing a factory reset and not doing any iCloud backup:

A few days after the factory reset while doing practically nothing on the iPad:

I also have an iPod with iOS 12 (not a fresh install), this is what it reports:

To me that looks roughly consistent with the numbers for the iPad.

Finally, this is what Apple states for iOS 14:

Available space is less and varies due to many factors. A standard configuration uses approximately 10GB to 13GB of space (including iPadOS and preinstalled apps) depending on the model and settings. Preinstalled apps use about 4GB, and you can delete these apps and restore them. Storage capacity subject to change based on software version and may vary by device.