baguette size and weight

... is that the definition of a baguette is that it is 250g.  Some are short and fat, some are long and thin --but they all weigh (or are supposed to) 250g.

As for the number of slashes, that will depend on low long your baguette is. Mine are 16" long as that is the length of my baguette pan.  Generally 5-7 cuts are enough to go end to end. Each cut overlaps the previous one by 25-30%

A baguette (pronounced /bæˈɡɛt/) is a specific shape of bread, commonly made from basic lean dough, a simple guideline set down by French law, distinguishable by its length, very crisp crust, and slits cut into it to enable proper expansion of gases and thus formation of the crumb, the inner soft part of bread. The standard diameter of a baguette is approximately 5 or 6 cm, but the bread itself can be up to a meter in length, though usually about 60 cm. A Parisian baguette typically weighs 250 grams (8.8 oz), but this is not legally regulated and varies by region[1]. It is also known in English as a French stick or a French bread.

There is a definition from wikipedia, as for the validity I'm not sure.  I do recall hearing that the number of slashes must be ODD, the French considered loaves with an EVEN number of slashes to be inferior. 

However, I scale most of mine around 454g prebaked for a 16" long baguette.

Darren