🔊 Port Length Calculator

The vented box port length formula

This calculator uses the standard Thiele-Small vented enclosure port length equation: L = (23562.5 × D²) / (Fb² × Vb) − k × D, where D is port diameter in cm, Fb is the target tuning frequency in Hz, Vb is net internal box volume in liters, and k is an end-correction constant that depends on how many ends of the port are flared (0 for none, 0.732 for one flared end, 1.463 for both).

If the diameter is too large or the box too small for the target frequency, the raw formula can produce a zero or negative length — a sign the port needs a smaller diameter or the box needs more volume, since a physically real port can’t have negative length.