Calculating speaker enclosure volume is a five step procedure.
(Make sure you do not forget to subtract the thickness of the wood that you have selected to use to build your enclosure.)
Step One: Measure Height
Step Two: Measure Width
Step Three: Measure Depth
Step Four: Height x Width x Depth
Step Five: Divide the results were in step four by 1728 (12" x 12" x 12"=1728 which equals to 1.0 cu ft.)
Complete formula should look like this Height x Width x Depth / 1728 =__________
Below are illustrated versions of all the steps that you should take.
(FOR EXAMPLE ONLY)
B U I L D I N G A N E N C L
Step One
12"
18"
19.5"
Step Two
13.5"
O
S U R E
Step Three
Side View
12"
13.5" 
Patent No: US D478,556 S
Patent No: US 6,601,645 B1
Patent No: US 6,656,000 B2
The wood that we are using is 0.75" thick
The 1.5 that you see in the formula is the thickness of the wood.
Calculating thickness of wood:
Measure how thick the wood is then multiply by two. The reason that you are multiplying by two is each side of the enclosure.
Left + Right=1.5
Top + Bottom=1.5
Front + Back=1.5
.75 x 2=1.50
18 x 12 x 12=2592
2592 / 1728=1.5
1.5 cu. ft. is the results for this enclosure
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