In for 4, hold for 4, out for 4, with no pause on empty lungs. An easy way into paced breathing.
Triangle breathing keeps three equal phases (inhale, hold, exhale) and leaves out the empty pause that box breathing adds at the end. Many people find that the missing fourth side makes the practice feel lighter, especially if holding the breath out makes them restless. At 5 breaths per minute, it is clearly slower than everyday breathing without being demanding.
Use triangle breathing when you want to calm down but stay alert: on a break at work, as a passenger on the way home, or before sitting down to meditate. It is a good first pattern if you have never tried structured breathing, and a sensible step before moving on to box breathing or longer holds.
Triangle breathing is a practical simplification of equal-count breathing rather than a named historical technique, and there is no research dedicated to it. What it shares with better-studied methods is a slower breathing rate and a regular rhythm. Slow, paced breathing in general has been associated with lower physiological arousal in laboratory studies.
Practice sitting or lying down; never in water or while driving. Stop if you feel dizzy.
If the 4-second pause leaves you short of breath, shorten it to one or two seconds. Stop and breathe normally if you notice tingling or dizziness.