The number of cables that can fit inside a J-channel cable concealer depends on several factors, including the size of the J-channel, the diameter of the cables, and how tightly the cables can be packed together. 
1. **Size of the J-Channel**: J-channels come in various sizes, typically measured by their width and height. Common sizes might range from 0.5 inches to 2 inches in width and height. The larger the J-channel, the more cables it can accommodate.
2. **Cable Diameter**: Cables also vary in diameter. For example, a standard Ethernet cable (Cat5e or Cat6) might have a diameter of about 0.2 to 0.25 inches, while a thicker HDMI cable might be around 0.3 to 0.5 inches in diameter. Smaller cables, like telephone or USB cables, will take up less space.
3. **Packing Efficiency**: The way cables are arranged inside the J-channel affects how many can fit. Cables can be laid flat, stacked, or bundled, impacting the total number that can be accommodated. 
To estimate the number of cables, calculate the cross-sectional area of the J-channel and compare it to the combined cross-sectional area of the cables. For example, if a J-channel has a cross-sectional area of 1 square inch, and each cable has a cross-sectional area of 0.04 square inches, theoretically, you could fit 25 cables. However, due to packing inefficiencies and the need for some space to maneuver the cables, the practical number might be lower.
Ultimately, the exact number will vary based on these factors, and it's often best to test with the specific cables and J-channel you plan to use.