Per the National Electrical Code Article NEMA 3929(b) cable tray fill calculations and cable tray sizing calculations will be computed as follows. Cable Trays may be filled 50% when using control or signal wiring. The sum of the cross sectional areas of all cables cannot exceed 50% of the trays fill area. The cable tray sizing equals the width times the loading depth. Generally, cable tray sizing is correct when it appears 50% full of cable or wire , or when it contains a 50% fill of cables or wire.
Wire Basket Cable Tray Fill Calculator  Cable Tray Sizing Calculator
Tray Size

# of 0.1852"
O.D. Cables 
# of 0.21"
O.D. Cables 
2" x 2"

74

57

2" x 4"

148

115

2" x 6"

222

173

2" x 6"

296

230

2" x 8"

296

230

2" x 12"

445

346

2" x 16"

593

461

2" x 18"

668

519

2" x 22"

816

635

2" x 24"

890

692

2" x 28"

1039

808

4" x 4"

296

230

4" x 8"

594

461

4" x 12"

890

692

4" x 14"

1039

808

4" x 16"

1187

923

4" x 18"

1336

1039

4" x 20"

1484

1154

4" x 24"

1781

1385

6" x 8"

890

692

6" x 16"

1781

1385

6" x 20

2227

1732
