Box Volume Calculator
Work out the real net internal volume of your cabinet after wood thickness, driver, port and bracing displacement.
Inputs
Magnet + basket + cone. Check the spec sheet (a 12″ is ~2–3 L).
Use 0 for sealed. Port area × length.
Typically 1–4% of internal volume
Your box
Where the volume goes
You lose 31% of the outer volume to walls and hardware.
How it works
The net internal volume is what a speaker actually “sees”, and it’s the number every box calculator asks for. It is always smaller than the volume of the outer cabinet.
Gross = W × H × D Internal = (W − 2t) × (H − 2t) × (D − 2t) Net = Internal − driver − port − bracing
Panels eat space at every wall, a ¾″ MDF box loses 1½″ in each direction. The driver’s magnet, basket and cone are sitting in the box, so their displacement is subtracted. Ports and braces do the same. Fill material (polyfill) does the opposite: it slows sound down, so a sealed box acts up to 10–15% bigger.
Converting between units: 1 ft³ = 28.317 L, and 1 L = 1000 cm³. Everything is computed in centimetres internally, so you can switch between metric and imperial without losing precision.