How much sugar can I put it my coffee before it's worse than soda? Coffee is generally quite healthy and soda is full of sugar. However people end up putting lots of sugar in their coffees. 

How much sugar is needed before a cup of coffee is worse than soda?
For my calculations I'll be using Coca Cola (which has 39 grams of sugar in a single can! (375ml))

For any amount of pure Coffee (no milk), you can put 39 grams of sugar or nearly 10 teaspoons of sugar, as Coffee has no sugar in it. 30ml is a standard espresso size so to be equivalent per ml of liquid you would need to put 3.1 grams of sugar which is less than a teaspoon.

One teaspoon in an espresso makes it contain a higher percentage of sugar than coke

For a 150 ml Cappuccino which is approximately 25 ml of coffee and 85 ml of milk, (Note that in a Cappuccino a portion of the volume is made up by froth which is why 85+25&lt;150). Approximately 4.5 grams of sugar is from the milk which means you can still add another 34.5 grams of sugar to be equivalent to a can of coke. And to be equivalent per volume (using 110ml as the volume since the froth doesn't count as it is essentially air) you would need to add an additional 7 grams of sugar (nearly two teaspoons).

Two teaspoons in a cappuccino makes it contain a higher percentage of sugar than coke