Box Fill

Box Fill Conductors #6 and Smaller

Area of a Triangle Triangles 30 60 90 Triangles 45 45 90 Pythagorean Theorem
Impedance Inductive Reactance Junction Box Straight Pull Junction Box Angle Pull
Junction Box Back of the Box Box Fill Box Fill Lookups Gutter Fill
Gutter Fill Percentage Geometry Home Electrician Math Home Electrician Education Home

Box Fill Calculations

Where a box is planned to contain conductors which are sizes #6 and smaller, then a volume calculation will allow you to determine the correct box size for the job. Usually this means finding the depth of a device box but it cal also mean determining the size of a junction box.

So a #14 AWG conductor is calculated at 2 cubic inches 

#12 AWG conductor 2.25 cubic inches

#10 AWG conductor 2.5 cubic inches

#8 AWG conductor 3 cubic inches

#6 AWG conductor 5 cubic inches

There are quite a few special considerations found in the NEC article dealing with box fill. Read article NEC 314 to refresh your memory of these details.

Note: Remember that pull boxes for conductors sized #4 and larger are determined based on raceway size, and not cubic inches.


Several box fill worksheets are available for practice on this topic. Click on a page number. The image will come up on your computer screen. You can press the print button to make a copy of the page. Click the Audio Support words to hear a description of the technique of solution.

63 Box Sizing    Audio Support

64 Junction Box Sizing    Audio Support

65 Box Fill - NM cable    Audio Support

66 Box Fill Story Problems    Audio Support

67 Box Fill Story Problems    

68 Box Fill Story Problems    

69 Box Fill Story Problems    

Click HERE to find out how to order a solutions key for all Journeyman problems on this website. Click HERE to find out how to order a solutions key for all Master Electrician problems on this website.



Many electrician workbooks and practice exams are now available 
as digital downloads for immediate use. 
Click HERE to see what is available.

Products For Sale
2006-2011 David U. Larson
Companion Website to , and
Other websites by David U. Larson which may be of interest: