Baby spinach leaves are about 40-50mm which is early picked spinach, which the leaves get to about 100-150mm which is often called "English Spinach".
In South Australia, spinach is actually a different variety which gets to about 200mm and is a little more like silverbeet.
English Spinach bunches weigh approx 400g but full bunches weigh about 800g, spinach can be picked about 3 times if the roots are not disturbed, first pick is soft & sweetest but degrades rapidly, pick 2 is the best, pick 3 is often stringy.
Oh by the way I work for a guy that grows and sells spinach at the fruit and veg market

Bet your sorry you started this thread