Turn Rate is the speed at which a unit can turn. Every unit has a base turn rate, which can be lowered by a few rare Turn Rate Slow abilities. Turn rate is an important mechanic because heroes are required to be within 11.5° of facing the target position in order to perform an action, such as moving, attacking, casting spells, or using items. This means performing actions is not instant and there is a delay between the time it takes to turn and when the required position is reached. Because the 11.5° leeway is in either direction, this creates a 23° angle directly in front of the hero allowing instant actions on any target within 23°.
Turn rate exists to allow reaction time to respond in most cases. It also increases importance of positioning, as a prepared action will be faster than an unprepared action made by a unit facing the wrong direction. For example, an instant cast ability on the fastest turning heroes will come out 0.08 seconds late if facing away from the target. If it had faced directly at the target in this scenario (within 23° of the caster's front) the action would have come out instantly at 0 seconds. While these numbers seems small, they have a noticeable effect in game and frequently determine the outcome of close calls. The most famous case of this in action is the "Million Dollar Dream Coil" that won Alliance TI3. It involved pro player s4 as Puck canceling Templar Assassin's teleport back to base at the last possible moment, shown here. Note how the teleport timer in the middle of the screen displays 0.0 seconds left, yet Puck was still able to cancel it in time.
The vast majority of heroes have a turn rate between 0.5 and 0.6. Io is a special case in that it does not require turning for performing actions. It will attack, cast, and move instantly no matter its facing, but still uses turn rate for directional modifier purposes, and always attempts to turn regardless of not requiring turns for actions.
Turn Rate Formula
Turn rate is expressed in radians per 0.03 seconds. A 180° turn is 3.14 radians.
Finding the time to turn 180° can be calculated using the following formula:
0.03 × 3.14 = 180° Turn Time
However due to the 11.5° leeway, the maximum time it would take to perform an action is within 168.5° rather than a full 180°.
Finding the time to turn 168.5° can be calculated using the following formula:
0.03 × 2.94 = 168.5° Turn Time
In effect, this results in actions being allowed to occur 0.01 seconds earlier. While this number seems small, it has a noticeable in game effect. With directional turning, which forces a full 180° turn for precise movement, actions feel significantly slower. Overall, the leeway makes actions feel more fluid and less clunky.
Because the 11.5° leeway is in either direction, this creates a 23° angle directly in front of the hero allowing instant actions on any target within 23°. For any target beyond this angle, the hero must wait until they turn before the action occurs. The above formula is used to find the maximum time, so the time until the action takes place is ≤ 168.5° Turn Time.