Typical net box volume for 6.5", 6x9, 8", 10", 12", 15" and 18" subs, sealed and ported, for one to four subs.
Subs in the box
1
2
3
4
1
2
3
4
Net volume (after displacement), ft³, for 1 sub(s) in one box. Ported boxes are usually tuned to 30–36 Hz.
Subwoofer Box Size Chart: Sealed and Ported
Sub
Sealed
Ported
6.5"
0.15–0.3
0.25–0.5
6x9
0.25–0.5
0.4–0.75
8"
0.35–0.6
0.6–1
10"
0.6–1
1–1.6
12"
1–1.6
1.75–2.75
15"
1.75–2.75
2.75–4.5
18"
3–4.5
4.5–7
Your sub’s manual wins. These are common starting ranges, not a standard: two 12" subs from different brands can want very different boxes.
Starting points, not guarantees. Your sub’s manual wins: check its recommended box and tuning.
How it works
Pick how many subs share the box. The chart shows a typical net volume range for each sub size, sealed and ported. Start from your sub’s manual if it gives a volume; use the chart when it doesn’t.
Example: one 12" sub usually wants 1 to 1.6 ft³ sealed or 1.75 to 2.75 ft³ ported. Two 12s in one ported box: 3.5 to 5.5 ft³.
Then take the volume to the box calculator to get the outside size and the cut sheet, and to the port calculator for the port length.
Frequently asked questions
What size box for a 12 inch sub?
Typically 1 to 1.6 ft³ net sealed, or 1.75 to 2.75 ft³ ported, tuned around 32 Hz. Check your sub’s manual first.
What size box for two 12s?
Double the single-sub volume: about 2 to 3.2 ft³ sealed or 3.5 to 5.5 ft³ ported, net.
Sealed or ported?
Sealed is smaller and tighter. Ported is louder for the same power and goes deeper, but the box is bigger and needs a port.