Here in the States, we only have loose designations like "sport" or "fingering" to help us understand the thickness of the yarn for sale. Hopefully other countries have managed to do it better. Anyway, cone yarn is a far, far better deal than balls but its labelling scheme is completely different. I won't go into details because the explanation is somewhat lengthy and not relevant to my point. The size of a coned yarn is given as a fraction that indicates plies and number of yards to make up a certain weight or something. You will see sizes like 2/16, 3/8, 2/20, etc. The important information is how many yards make up a pound, which should be included in the product information. A 2/20 yarn may give 5600 yards per pound.
Now put it into perspective. Using a yarn you are familiar with, get the ball weight and yardage from the label. Find the weight in ounces if it's not given, and convert it to pounds. Find the total yardage in one pound.
For example, a 50g ball of "fingering" weight yarn contains 231 yards. 50 grams is 1.76 ounces so 16/1.76 is 9.09. Multiply 231 by 9.09 and you have 2099.79 yards per pound (ypp). Compare to a 2/8 cone yarn that has 2240 ypp. The ypp goes down as the yarn gets thicker.
Now determine the price per pound to learn just how bad a deal hand knitting yarn really is. A lace weight ball may cost $7 (and up!!) for 25g. That works out to $127.26 per pound (6764ypp). A 2/30 yarn has 8147ypp. Most coned yarns are $20-40 per pound depending on how fancy the yarn is. Since cone yarn is sold by the pound, the yardage and number of plies doesn't affect the cost. Plus you don't have to worry about dye lots or not buying enough balls for your project, as you will likely get many projects out of one cone. You can also double up finer yarns if you can't find a cone yarn of a suitable thickness for your project, opening up all kinds of interesting color and texture combinations.
