The first thing you need to do is to measure the distance between your nose and your extended hand with a tape measure. This will be your personal measurement and you should keep the information handy.
Pull out what you think is a good estimate of the amount you believe you will use. If it is a large project and you think you will need more then one skein then just estimate the number of skeins and then use this method for the end of the last skein.
Begin your project keeping track of the number of skeins you use as you go.
On the last skein use your personal measurement and after pulling out several of those measurements, nose to extended hand, tie a knot in the yarn at the end of this measurement. Continue to work your project. If you complete the project before the knot, measure the distance that is left unused. Now you need to multiply the number of personal measurements you pulled out by the inches in your personal measurement. Then minus the inches that were used from those you originally pulled and that is the amount of yarn you will need.
But if you reach the knot first and need more then remove the knot and tie another until you complete the work. Don't forget to keep a record of the extra lengths you pull out.
I believe this system would work best on small projects. As you do this remember that this is all personal to you, to your guage, type of yarn you used, and hook size.
If this is not clear and you need a better understanding then you can Google "Length measurement when using yarn". There will be a lot of help for you there under this heading. One link I looked at was Estimate Yardage.
Hope this helps. If not it should at least give you a direction to head in for more information regarding this subject.
That's it today. Ghost, OUT!