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Approximate Number of Wires in Conduit

Chart for Thhn wire Check Code Book for actual types and charts;
************************************************************************************        
|    1/2    |    3/4    |    1    |   1-1/4  |  1-1/2  |   2    |   2-1/2  |   3   |
|-----------|-----------|---------|----------|---------|--------|----------|-------|
| AWG #wire | AWG #wire | AWG#wir | AWG#wires|AWG#wires|AWG#wire|AWG#wires |AWG#WRs|
|  14 (13)  |  14 (24)  | 14 (39) |  14 (69) | 14 (94) | 14(154)| 14       |       |
|  12 (10)  |  12 (18)  | 12 (29) |  12 (51) | 12 (70) | 12(114)| 12(164)  |12(   )| 
|  10 (6)   |  10 (11)  | 10 (18) |  10 (32) | 10 (44) | 10(73) | 10 (104) |10(160)|
|   8 (3)   |   8 ( 5)  |  8 ( 9) |   8 (16) |  8 (22) |  8(36) |  8 ( 51) | 8( 79)|
|   6 (1)   |   6 ( 2)  |  6 ( 6) |   6 (11) |  6 (15) |  6(26) |  6 ( 37) | 6( 57)| 
|   4 (1)   |   4 ( 1)  |  4 ( 4) |   4 ( 7) |  4 ( 9) |  4(16) |  4 ( 22) | 4( 35)|
|   3 (1)   |   3 ( 1)  |  3 ( 3) |   3 ( 6) |  3 ( 8) |  3(13) |  3 ( 19) | 3( 29)|
|   2 (1)   |   2 ( 1)  |  2 ( 3) |   2 ( 5) |  2 ( 7) |  2(11) |  2 ( 16) | 2( 25)|
|   1       |   1       |  1 ( 1) |   1 ( 3) |  1 ( 5) |  1( 8) |  1 ( 12) | 1( 18)|
************************************************************************************ 
The number of conductors shall not exceed the percentage fill specified in table 1, chapter 9. (fpn) for conductor cross sectional area see tables: 5,5a,6,7,8 and the applicable notes to tables at the beginning of chapter 9.

The maximum percentage of conduit fill for more than three conductors in a conduit or raceway is 40 percent. (all conductors except lead covered)

Units of area:
The circular mil is the unit of cross section used in the American wire gauge (AWG). The term Mil means one thousandth of an inch (0.001 inch). A circular mil is the area of a circular wire with a diameter of one mil, 0.001".

The circular mil area of any solid cylindrical wire is equal to its diameter (expressed in mils) squared. For example, the area in circular mils of a wire having a diameter of 3/8 of an inch (0.375) equals 375 x 375 = 140,625 CM. The diameter in mils of a solid circular wire is equal to the square root of its circular mil area. Assuming that a conductor has an area of 500,000 CM, its diameter in mils is the square root of 500,000, which is equal to 707 mils, or 0.707 inch (approximately). The area in square inches of a wire whose diameter is one mil is Pi D squared /4 = 0.7854 x 0.001 squared = 0.0000007854 sq.in.

The square mil is the area of a square whose sides are each one mil (0.001 inch). Hence, the area of a square mil is 0.001 squared, or 0.000001 square inch. With reference to the previous definitions of the circular mil and the square mil, it is obvious that in order to convert a unit of circular area into its equivalent area in square mils the circular mil must be multiplied by Pi/4, or 0.7854, which is the same as multiplying by 1.273.

These relations may be written as:

Area = diameter squared = circular mils (CM)
Square Mils = circular mils times 0.7854 = circular mils divided by 1.273.
Circular mils = square mils divided by 0.7854 = square mils times 1.273.

By this method any circular conductor may be converted into a rectangular conductor (a bus bar) containing an equivalent area or current carrying capacity.

Table 5 of the NEC gives the approximate area in circular mils and square mils of different sizes of wire. Top of Page