Inconsistent Size of MKV Files

[ds_tx]

How can I decrease size of MKV files?
I thought converting to MKV files was supposed to decrease file size by 40%.
But one blu ray disk inflated from 35GB to 62GB.
Another disk at 40GB only decreased to 36GB.

Am I using software correctly?
When I open MakeMKV, I have to click on video camera icon on far left to select source.
When I select blu ray disc, I have to select from contents.
When I select BDMV, I get message about that not working do I want to select disc instead and I click yes.
Then the titles load and a button appears on far right for Make MKV, which I click.

Previously, I tried clicking on folder to make a backup, but that wouldn't play very well in VLC player,
And that's not the way to make MKV is it?

[Woodstock]

MakeMKV copies data, it doesn't recode video. It can recode some audio types to be more compatible with players, but it leaves the video alone. Titles can get smaller by not including tracks within them that you don't need, but rarely by a significant amount.

Recoding the files using tools like handbrake will actually change the size. Depending upon the source, the change can be 80%, or it could be only a few percent.

[ds_tx]

Then why does the About MKV page state —
"MKV files are compact. For exactly the same content MKV files are about 10% smaller than DVD files and roughly 40% smaller than Blu-ray files."
/aboutmkv/

If the above is true, then why did MKV rip a 35GB blu ray movie to a 62GB file?
And a 40GB movie to a 36GB file?

[Woodstock]

Are you sure of the source file sizes? With "seamless branching", titles can be made up of dozens of files from the disk, and MakeMKV will combine all of them that make up a particular title.

"Compact" in your quote probably refers to comparing the MKV files extracted from a DVD or BD to an ISO of the same data, but I wasn't the author of that document, so what Mike meant to say is a question for him.

[ds_tx]

So how can I ask Mike?
I'd like to know how to rip bluray so files are smaller than disk.
I especially want to rip so files don't nearly double in size compared to disk?
What would cause that?

[Woodstock]

Mike will probably read this message thread soon - he's not here every day, but he does come by.

In watching MakeMKV work for the past few years, I have yet to see the file written to disk be bigger than the reported size on the DVD or BD, so I can't confirm or deny what you're seeing.

[ds_tx]

The online instructions and screenshots for using MakeMKV seem to be for Windows, as there's no way to select drive or volume source on Mac.
That's why I included info on how I used MakeMKV to make file.
Try using MakeMKV on Mac for Batman Begins, a 35GB bluray dvd and see what happens.
I ended up with 60+GB file.
The instructions for Terminal command to make VLC player use MakeMKV lib files to play bluray didn't work for me.
I had to MakeMKV file to play disc from my Mac, but the disc was inflated to nearly double in size instead of shrinking in size.