Your box is smaller inside than you think
“Box volume” in the sealed-box and port calculators means net internal airspace — not the outside dimensions of the box you're cutting. This walks the real conversion: external minus wall thickness, minus whatever the driver, port and bracing take up inside. Every figure traces to this site's enclosure-design research notes.
External box dimensions
Defaults to 0.75in — standard 3/4" MDF, the baseline material per the enclosure knowledge base.
Driver displacement
The 8/10/12/15" values are fallback estimates from cross-referenced sources — always prefer your driver's actual published displacement if you have it. No 18" preset: two real published 18" drivers found during review disagreed by over 60% (0.24 vs 0.39 ft³) — too wide a spread for a responsible single fallback. Use Custom for 18" and larger drivers, and for 6.5" drivers, which have no estimate here: enter your driver's own published figure.
Port displacement (optional)
Don't know your port length yet? Leave this on "no port yet," get your net volume, then run the Port Calculator — its result will be close enough that re-checking port displacement afterward rarely changes the tuning meaningfully.
Bracing displacement (optional)
Only matters for large brace panels, not thin dowel bracing. Estimate one brace as (length × width × thickness, in inches) ÷ 1728, and sum if you have more than one. Leave at 0 if bracing is minimal.
Fill in the external dimensions and driver info, then hit Calculate.