Cost a cup in two minutes and see the price that keeps your margin.
As a working guide, aim for 25% or less of the price excluding GST; 25 to 30% is worth watching; over 30% is high. This covers coffee, milk, cup and lid, not labour or rent.
The starting amounts are 180ml for 6oz, 300ml for 8oz, 360ml for 12oz and 480ml for 16oz. Change them to match your actual pour.
Milk left in the jug, spills and remakes still cost money. The 10% allowance covers that. Turn it off if your milk amounts already include waste.