Work out conduit fill for Cat6, Cat6A, fiber, coax and other low-voltage cables. Mix cable types in one conduit, check a conduit you already have, or find the smallest size that fits.
Cable diameters are typical values. Change any diameter to match your cable datasheet.
How the calculator works out fill
Each cable takes up a circle of space inside the conduit. The calculator finds that area from the cable’s outside diameter (area = 0.7854 × diameter × diameter), adds up every cable in the list, and compares the total with the inside area of the conduit you picked.
The limit depends on how many cables share the conduit: 53% for one cable, 31% for two, and 40% for three or more. These are the fill percentages in NEC Chapter 9, Table 1, and they are the limits normally used when sizing conduit for structured cabling. Conduit inside areas come from NEC Chapter 9, Table 4. Switch to the 30% target if you want room to add cables later.
The pull check is separate from fill. Common practice for telecom pathways is no more than 100 ft (30 m) and two 90° bends between pull points. Past that, cables are hard to pull without damage even when the fill percentage passes.
Cable diameters used
| Cable | Typical outside diameter | Area |
|---|---|---|
| Cat5e UTP | 0.20 in (5.1 mm) | 0.0314 in² |
| Cat6 UTP | 0.24 in (6.1 mm) | 0.0452 in² |
| Cat6 shielded | 0.27 in (6.9 mm) | 0.0573 in² |
| Cat6A UTP | 0.35 in (8.9 mm) | 0.0962 in² |
| Cat6A shielded | 0.32 in (8.1 mm) | 0.0804 in² |
| Duplex fiber | 0.20 in (5.1 mm) | 0.0314 in² |
| RG6 coax | 0.27 in (6.9 mm) | 0.0573 in² |
| RG59 coax | 0.24 in (6.1 mm) | 0.0452 in² |
| 18/2 control cable | 0.16 in (4.1 mm) | 0.0201 in² |
| 22/4 alarm cable | 0.15 in (3.8 mm) | 0.0177 in² |
| Access control composite | 0.45 in (11.4 mm) | 0.1590 in² |
Plenum, shielded and outdoor versions of the same cable are often thicker. Always confirm against the manufacturer’s datasheet before you order conduit.
Questions about conduit fill for data cable
How many Cat6 cables fit in a 1 inch conduit?
Seven Cat6 UTP cables fit in a 1 inch EMT conduit at the 40% limit, based on a 0.24 inch cable. At the 30% design target the number is five. A 1 inch PVC Schedule 40 conduit also holds seven.
Can I run Cat6, fiber and coax in the same conduit?
Yes. Add each cable type as its own line and the calculator totals the areas. Data, fiber, coax and alarm cables can share a conduit. Keep them out of any conduit that carries power wiring.
Why is the limit lower for two cables than for three?
Two cables sit side by side across the conduit and wedge more easily than a bundle of three or more, so the limit for two cables is 31% compared with 40%. A single cable is allowed 53%.
My cable is a different diameter. What should I do?
Type your cable’s outside diameter into the diameter box on that line. The value is on the manufacturer’s datasheet, usually listed as nominal OD. Cat6A in particular ranges from about 0.27 to 0.35 inches depending on the brand and shielding.
How long can a conduit run be before it needs a pull box?
Common practice for telecom conduit is a pull point at least every 100 ft (30 m) and after every two 90° bends. Enter your run length and bends in the pull check to see if your run is inside that guidance.
Does this calculator work for electrical wire?
No. It is built for data and low-voltage cables, which are sized by outside diameter. For THHN, RW90 and other building wire, use our conduit fill calculator for electrical wire.