We pour all of our wines BTG in 1.5, 3.0 & 5.0 portions.
With a 750ML bottle = 25.4oz, to us 5.0 is a standard "glass" of wine. The 3.0oz size is essentially a half glass and the 1.5oz portion is a great way to taste many over the course of a night and to build your own flight.
We sell almost equal amounts of the 1.5, 3.0 & 5.0 portions. All the wines BTG are priced proportionately, ie there is no premium for small pours (ex - 1.5oz = $3.00; 3.0oz = $6.00; 5.0oz = $10). We do charge a small premium over the full bottle price to make up for overpours and other waste (ex, a wine that is $10/glass would be priced at about $42/bottle). The exact bottle price is based on the "retail" price of the wine + $20 ($15 if the "retail" price is < $20). We calculate the bottle price first and then go back and determine the BTG prices from that.