Soaking a brand new rope

Before starting to use your brand new ropes, you have to do the "sinking" process. So, what's that ?
Is the process of real lenght measurement actually.
So, a serious producer will sell you a surplus of a few meters to assure that you get your desire lenght after the shrinking process.
This is usually true when you buy fixed rope lenght on rope drums. If you go and buy a few meters of ropes just by cutting from a long one, you won't get the surplus either because the sellers don't know about shrinking or because you want 10 meters and why should they sell you 11 or 12... . So, better buy rope drums.

So, starting over, first thing you should do with a brand new rope is to sink it for at least 24 hours in water. Changing water every few hours is also important. If flowing water is available is even better. Beside the soaking process, washing a new rope before it's first use is recommended to remove also any chemicals left on the surface of rope.
Don't use too hot or too cold water !

After these 24 hours, let your rope dry complete. It may take 3 days. Don't dry it in sunlight or with some artificial heating systems. Let it dry slowly in a dark place with enough airflow for rope to "breathe". After that, you can finally measure it for final marking. Like I said before, a serious manufacturer will sell you more rope than you ordered to assure that you get your desire lenght.
Two real life examples:
1) Edelrid Superstatic LinkTec 9,1mm.
The fixed drum of 50 meters had actually 52 meters before sinking in water.
2) Simond Stat 9mm: the 100m rope drum contained 107meters of rope actually.
After "washing" these new ropes and letting them dry, the lenght were according to their claim: 50 m and 100 m. There is one company that claim their ropes are ready to use right from the rope drum: Korda's from Spain.
The not so nice part is when you buy 100m and you get exactly this lenght. After soaking it, you realise that you bought only 93 ameters.
A wonderful and complete guide about rope and their manufacturing process you can download here.