Bike Stem Calculator
This calculator will help you determine how different bike stems will change your handlebar position.
A bike's stem is generally identified by the stem length (measured from the center of the steerer clamp to the center of the handlebar clamp) and the stem rise angle (measured from a line perpendicular to the steerer clamp).
Since the fork or head tube angle isn't absolutely vertical the stem makes a different angle relative to the ground once installed.
On threadless stems, spacers can be added to or removed from the steerer tube to raise or lower the stem, and therefore the handlebars. On quill stems, a similar effect can be achieved by raising or lowering the stem extension (much like raising or lowering the height of your seat by inserting more or less of the seat post into the seat tube).
This calculator will help you determine the net stem angle (relative to the ground), stem height (vertical distance above the head tube clamp) and stem reach (horizontal distance from head tube clamp) for a given stem length, stem rise angle, head tube angle and spacer (or extension) height.
To learn more about bike stems, see Brightspoke's article Understanding Stems.