If you want more coffee in your cappuccino or prefer to spend as little as possible at Starbucks - order 8 oz "short" cappuccino instead of the regular 12 oz.
Why?? The 8oz "short" cappuccino from Starbucks has the same amount of espresso as the tall 12 oz, meaning that your coffee get simply more milk. ( yeah, you pay "coffee" price for extra milk)
Now why you get only 8 ox cappuccino in 12 ( or even 16 oz ) cup? Because Starbucks must maintain a fine line with pricing, so they sell you 8 oz coffee with ... lots of milk, and you pay for 12 oz drink.
If you ask why they just don't make, say 12 oz cappuccino? Because it is impossible to properly froth the microfoam in larger quantities.
The mystery of the "short" cappuccino. - Slate Magazine
Cappuccino | Starbucks Coffee Company