How to know the percentage of the methanol without using hydrometer?

If you have a good scale, and an accurate thermo, you can check SG, from what I gather.

One liter of water will weigh 1000 grams at 20C.
One liter of methanol will weigh 792 grams at 20C.
This is the Specific Gravity. Assuming water is the only contaminant your actual weight can be calculated as a percent.

Here is an excellent chart for purity thanks to Graham Laming. It is scaled for different temperatures too.

It's that simple.

Bob

Thanks!for good advise!